Vocabulary Atomic Structure. anion ___ are negatively charged ions - atoms that take electrons.
ATOMIC STRUCTURE electron configuration of atoms and ions of the
description
Transcript of ATOMIC STRUCTURE electron configuration of atoms and ions of the
ATOMIC STRUCTURE
electron configuration of atoms and ions of thefirst 36 elements (using s,p,d notation)
periodic trends in atomic radius, ionisationenergy and electronegativity
comparison of atomic and ionic radii
Electron Electron arrangements in the arrangements in the
atomatom
Boundary Surfaces of the Boundary Surfaces of the 4f4f Orbitals Orbitals
Energy levels, sub-levels and orbitalsEnergy levels, sub-levels and orbitals
Energy levels• Electrons occupy distinct energy levels (or
shells) arranged around the nucleus.
• The different main energy levels have different sub-levels in them
There are four types: s, p, d, f
Energy sub levels
• The number of sublevels is determined by the energy shell. One in Level 1, 2 in Level 2 etc
Orbitals
• Electrons occupy orbitals in pairs, with each member of the pair having opposite spin, which cancel.
• s sublevel has 1 orbital• p sublevel has 3 orbitals• d sublevel has 5 orbitals • f sublevel has 7 orbitals
Number of orbitals
A Cross Section of the Electron A Cross Section of the Electron Probability Distribution for a Probability Distribution for a 3p3p Orbital Orbital
1s
2s
2p 2p 2p
3s
3p 3p 3p
3d 3d 3d
Level 1 has just 1 sublevel consisting of one orbital (1s)
Level 2 has 2 sublevels (s and p) with one orbital in the first (2s) and 3 orbitals in the second (2p)
Level 3 has 3 sublevels (s,p and d) with one orbital in the first (3s), 3 orbitals in the second (3p)And 5 orbitals in the third (3d)
3d 3d
Energy Orbital arrangements in Atoms
Energylevel
1s
2s
2p
3s
3p
3d 4sn=4
n=3
n=2
n=1
Write the order of subshell filling using the graph1s 2s 2p 3s 3p 4s 3d
What atom is this?
Ne
Electrons fill orbit of lowest energy first.
Electron Arrangements in Orbitals
•In the normal ground state of an atom, the electrons occupy orbitals with the lowest possible energies. On heating, the electrons can be excited to orbitals with higher energy - the ‘excited state’.
•As the electrons fall back to lower energy levels (orbitals) they will emit electromagnetic radiation, which is often in the region of visible light ie. it appears coloured.
• Each element has its own characteristic emission spectrum that can be used to identify that element, its “chemical fingerprint”.
Atomic orbitals define regions of space in which there is a high probability of finding an electron.
Each orbital has a particular shape and associated energy values.
1.Each orbit can hold 2 electrons only an orbital containing two electrons is a filled orbit
2.Electrons filling the same orbit must have opposite spins indicated by arrows
3.Electrons fill the lowest energy sublevels first
4.The lowest or most stable arrangement of electrons in a sublevel is the one with the greatest number of parallel spins (Hunds Rule)
5.This means when orbitals of the same energy are available, electrons will avoid pairing if possible, by entering separate orbits
Rules For Filling Orbits
Energylevel
1s
2s
2p
3s
3p
3d 4sn=4
n=3
n=2
n=1
the electron configuration for Ne using the correct format is :
The Electron Arrangement for Ne is
1s2 2s2 2p6
Energylevel
1s
2s
2p
3s
3p
3d 4sn=4
n=3
n=2
n=1
Write the electron configuration then name the atom
Electronic Configuration - ways Electronic Configuration - ways to write themto write them
O: or
Cl: or
K: or
The electrons in the outermost shell of an atom are called its valence electrons
O: [He] 2s2 2p4
Core electrons Valence electrons
1s2 2s2 2p4 [He] 2s2 2p4
1s2 2s2 2p6 3s2 3p5 [Ne] 3s2 3p5
1s2 2s2 2p6 3s2 3p6 4s1 [Ar]4s1
Energylevel
1s
2s
2p
3s
3p
3d 4sn=4
n=3
n=2
n=1
[Ar] 4s2 3d2
Write the Electron Arrangement for Ti
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel11 ss
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
pp
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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33
ss 11 22
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dd
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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33
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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33
ss 11 22
pp 33 66
dd 55 1010
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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33
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1818pp 33 66
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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1818pp 33 66
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
88pp 33 66
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ss 11 22
1818pp 33 66
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ss 11 22
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Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. of Max. no. of electron electron pairs in pairs in
sub-levelsub-level
Max. no. of Max. no. of electrons electrons in sub-in sub-levellevel
Max. no. of Max. no. of electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
88pp 33 66
33
ss 11 22
1818pp 33 66
dd 55 1010
44
ss 11 22
pp 33 66
dd 55 1010
ff
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. Max. no. of of
electron electron pairs in pairs in
sub-levelsub-level
Max. no. Max. no. of of
electrons electrons in sub-in sub-levellevel
Max. no. Max. no. of of
electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
88pp 33 66
33
ss 11 22
1818pp 33 66
dd 55 1010
44
ss 11 22
pp 33 66
dd 55 1010
ff 77
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. of Max. no. of electron electron pairs in pairs in
sub-levelsub-level
Max. no. of Max. no. of electrons electrons in sub-in sub-levellevel
Max. no. of Max. no. of electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
88pp 33 66
33
ss 11 22
1818pp 33 66
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44
ss 11 22
pp 33 66
dd 55 1010
ff 77 1414
Energy levels and sub-levelsEnergy levels and sub-levels
Main Main energy energy levellevel
Sub-Sub-levelslevels
Max. no. of Max. no. of electron electron pairs in pairs in
sub-levelsub-level
Max. no. of Max. no. of electrons electrons in sub-in sub-levellevel
Max. no. of Max. no. of electrons electrons in main in main
levellevel
11 ss 11 22 22
22ss 11 22
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33
ss 11 22
1818pp 33 66
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ss 11 22
3232pp 33 66
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ff 77 1414
Atomic OrbitalsAtomic Orbitals
Main energy Main energy levels, levels, nn
Energy Energy sub-sub-
levels, llevels, lOrbitalsOrbitals
Number of Number of electronselectrons
11 11 11ss 22
22 22 22ss22pp
22
66
33 33 33ss
33pp
33dd
22
66
1010
44 44 44ss
44pp
44dd
44ff
22
66
1010
1414
The order in The order in which the which the orbitals fill in orbitals fill in atomsatoms
Hydrogen 1s, Hydrogen 1s, 2s, and 3s 2s, and 3s OrbitalsOrbitals
Three Three 2p2p Orbitals Orbitals
Boundary Surfaces of the Boundary Surfaces of the 3d3d OrbitalsOrbitals
Energylevel
1s
2s
2p
3s
3p
3d 4sn=4
n=3
n=2
n=1
[Ar] 3d10 4s1
Write the Electron Arrangement for Cu
Copper has a unique electron configuration
Extra stability is gained when the 3d orbitals are half filled or completely filled
Energylevel
1s
2s
2p
3s
3p
3d 4sn=4
n=3
n=2
n=1
[Ar] 3d5 4s1
Write the Electron Arrangement for Cr Extra stability is gained when the 3d orbitals are half filled or completely filled
Chromium has a unique electron configuration
Orbitals Being Filled vs. Position in Periodic TableOrbitals Being Filled vs. Position in Periodic Table
Atomic and Ionic Radii
It is impossible to measure the atomic radius of an atom but we can measure the distances between adjacent nuclei in substances
In metals we look at half the distance between adjacent nuclei
In non metals we look at covalent bonds - that is half the distance between nuclei of like atoms covalently bonded together
Half this distance between nuclei
Ionic radiiRadii decrease across period
Radii increase down group
2006 Bonding Exam2006 Bonding ExamWrite the electron configuration for:Write the electron configuration for:
Cr Cr
MnMn
MnMn2+2+
Evidence AchievementAchievement with Merit
Two correct..Cr 1s22s22p63s23p64s13d5 OR [Ar] 4s13d5 OR [Ar]3d54s1
Mn 1s22s22p63s23p64s23d5
OR [Ar] 4s23d5 OR [Ar]3d54s2
Mn2+ 1s22s22p63s23p63d5 OR [Ar] 3d5
Trends in atomic and ionic radii
From your diagram for non transition elements note that:
Atomic and ionic radii increase going down a group because there are more electrons added as we move down a group
We surprisingly find radii decrease across a period .This is because as we go across a period the electron shells are pulled closer into the nucleus
Why are they pulled closer. Bridget?
Because the number of electrons in the outer shell and the number of protons in the nucleus also increase.
All the electrons in the shell are about the same distance from the nucleus, so adding extra electrons isn’t going to make much difference
But as we increase the number of protons in the nucleus the electrostatic attraction from the nucleus becomes greater on the outer shell electrons pulling them closer
Why do radii decrease moving across the period (row)
Each atom in the group has the same number of valence electrons and the same effective nuclear charge from the nucleus on these valence electrons.
But there are more electron shells as we go down the group.
Because the outer shells are protected or shielded from the nucleus by the inner electrons the valence shells end up further away from the nucleus and therefore the electrostatic attraction between the valence electrons and the nucleus decreases
Why the atomic Radii increase down a group
Ionic Radii
Ionic radii of negative ions are larger than their corresponding atom
As more electrons are added to the same number of protons repulsion pushes the valence electrons further apart.
The more negative the ion the larger it is eg N 3-
Ionic Radii
Ionic radii of positive ions are smaller than the corresponding atom
Positively charged ions have lost electrons, but the number of protons remains the same ... so the remaining electrons are held more strongly than before
The more positive the ion the smaller it is eg Al 3+
2006 Bonding Exam2006 Bonding Exam Compare the relative sizes of the CaCompare the relative sizes of the Ca2+2+ and Cl and Cl––
ions, and explain the difference in their radii.ions, and explain the difference in their radii.
Evidence AchievementAchievement with Merit
Cl– is larger or Ca+2 smaller.
Both have same number of shells or electron arrangement. Ca2+ has more protons or nuclear charge is greater, so the electrostatic attraction between the valence electrons and the nucleus is stronger, making Ca2+ smaller.
Correct size. Size and explanation correct.
Emission spectraof a hydrogen electron
Let us begin by examining the figure on the left that represents the 'spectrum' of the hydrogen atom. In this spectrum, each line represents a state or 'energy level' in which the hydrogen electron can exist, and the arrows indicate possible transitions between these energy levels.
When a hydrogen electron in one energy level makes a transition to a lower energy level, it emits energy in the form of photons, and the wavelength (or colour) of the emitted light is completely determined by the energy difference between the two levels. The spectrum of light shown below arises because the atom 'falls' from various higher states to the second lowest state. The lowest state is called the ground state.
Ionisation Energies
Define the term “Ionisation Energy” “The energy required to remove the
least tightly held electron from each atom of one mole of gaseous atoms or ions”
Do you think ionisation energies are always endo or exothermic Hannah?
Ionisation Energies
Ionisation energy is measured in kJ mol-1
The first ionisation energy of an atom is the energy to remove the 1st electron from the atom
The second ionisation energy removes the second electron
The first ionisation energy of Neon is +2087 kJmol-1
The thermochemical equation for this is written as:
1. Ne (g) Ne+ (g) + e H = +2087 kJmol-1
The second ionisation energy of Neon is +6128 kJmol-1
2. Ne+ (g) Ne2+ (g) + e H = +6128 kJmol-1
The second ionisation energy is higher because an electron is being removed from a positive ionWhy is the second ionisation energy always larger
than the first IE ? Daniel
We can tell the electronic structure of a K atom from its successive ionisation energies
Can you see how?
Remember the ionisation exercise last term – turn to it please
You have graphed the ionisation energies
now lets look at the questions
Recognising Periodic Ionisation Trends
As you go down a group the ionisation energies go down
eg He, Ne , Ar, Kr
The general trend across a period is of increasing ionisation energies eg Na to Ar
The zig zag shape of the graph indicates some atoms are more stable than others
The first ionisation energy of aluminium is 578 kJmol-1
Write the thermodynamic equation for this data:1. Al (g) Al+ (g) + e H = 578 kJmol-1
2. Explain why the first ionisation energy of :
a. Argon is lower than that of neon
b. Lithium is lower than that of neon
The valence electrons of argon are further away from the nucleus than those of neon, so it takes less energy to remove one from argon than neon
Lithium’s nuclear charge is +3, while neon’s is +10, so neon’s valence electrons are held more strongly than lithium’s
Answer these
Extension questions – Ionisation Energy Trends
Electron Configurations beyond Ar
The 4s orbital has slightly lower energy than the 3d orbitals, so the 4s orbital is filled before the 3d orbital
3d
K
Ca
4s
[Ar] 4s1 [Ar]
4s 3d
[Ar] [Ar] 4s2
Electron Configurations Of Transition metals
The 10 elements beyond Ca are called the transition metals and are found in the middle of the periodic table, almost all (except Cu and Cr) have 2 electrons in the 4s orbital
Electron Configurations Of Transition metals 3d
Sc
4s
[Ar] 3d1 4s2 [Ar]
Ti [Ar] [Ar] 3d2 4s2
V [Ar] [Ar] 3d3 4s2
Cr [Ar] [Ar] 3d5 4s1
Mn [Ar] [Ar] 3d5 4s2
Fe [Ar] [Ar] 3d6 4s2
Co [Ar] [Ar] 3d7 4s2
Ni [Ar] [Ar] 3d8 4s2
Cu [Ar] [Ar] 3d10 4s1
Zn [Ar] [Ar] 3d10 4s2
Write the electron configurations for the following
a. 7N3-
b. 33As
c. 28Ni2+
d. 24Cr
e. 35Br -
f. 12Mg2+
1s2 2s2 2p6
[Ar] 3d10 4s24p3
[Ar] 3d8
[Ar] 3d5 4s1
[Ar] 3d10 4s24p6
1s2 2s2 2p6
StarterReferring to your graph of atom radii (previous slide)
Why do atomic radii decrease as we move across a period?
As we move across a period an extra electron is added to the same shell while at the same time an extra proton is added to the nucleus.
The added electron is about the same distance away from the nucleus as the other outer shell electrons.
This means that there is a stronger electrostatic attraction from the nucleus on these outer shell electrons these electrons are then pulled closer to nucleus reducing the atom radius.
Referring to your graph of atom radii Why do atomic radii increase as we move
down a group? Give points
As we moving down a group an extra electron is added to a *different shell (further from the nucleus) while at the same time an extra proton is added to the nucleus.*most important
The added electron is shielded from the nucleus by the inner electrons.
Because of this the electrostatic force between the valence electrons and the nucleus decreases and the valence shells end up further away from the nucleus creating a larger radius
Remember the 4s orbital fills first and also empties first
Variable Oxidation states of MnVariable Oxidation states of Mn
Use the expt sheet Use the expt sheet
Transition Metal Colours
Transition MetalsTransition metals have varying oxidation states by holding on to or losing varying amounts of d electrons
Eg Fe2+ , Fe 3+
Cu +, Cu 2+
V 2+ , V 3+ , V 4+ , V 5+
Most transition metals have partially filled d orbitalsAnd can form coordination complexes with other species eg H2O, Cl , NH3 to name a few
When transition metal ions form diative bonds with the above species coloured complexes occur.
Transition Metal PropertiesTransition metals have variable _______ ______and most form ________ complexes eg The [Ti(H2O)6]3+ complex appears mauve because yellow green light is absorbed and a combination of visible light is reflected or transmitted to give a mauve colour
Another transition metal c_____ forms a complex ion with 6 H2O to give a ________ blue complex – name and give the formula of another Cu complexThese properties are due to the partially filled d subshell
opper[Cu(H2O)6] 2+
colouredoxidation states
[Cu(NH3)4] 2+ copper tetra amine
Transition Metal complex ions
They also form other complex ions in which the central metal ion is surrounded by other neutral molecules such as H2O or NH3, or by anions, such as Cl or OH. These are called ligands.
The non-bonded pairs of electrons on the ligands are donated to the metal cation and form co-ordinate (or dative) covalent bonds to the central metal ion.
This is all due to a partially filled ‘d’ shell
Transition Metal complex ions
The number of ligands attached to the central atom is called the co-ordination number.
For transition metals the most common co-ordination number is 6 and the complex ion has an octahedral arrangement.
[Fe(H2O)6]3+ [Co(NH3)6]
3+
cobalt(II) nitrate, Co(NO3)2 (red);
potassium dichromate, K2Cr2O7 (orange);
potassium chromate, K2CrO4
(yellow)
nickel(II) chloride NiCl2 (green)
copper(II) sulfate,
potassium permanganate, KMnO4 (purple).
CuSO4 5H2O
cobalt(II) nitrate,
K2Cr2O7
K2CrO4
nickel(II) chloride NiCl2
CuSO4 5H2O
potassium permanganate, KMnO4
.The colour we see is the light that is reflected after it is absorbed to elevate the electronsEg a hydrated Cu ion absorbs orange light and reflects blue
The 3d sub shell is split and allows for electrons to be elevated to orbits within the subshell often absorbing light in the coloured region.
The number of oxidation states generally increases with the number of unpaired electrons, with elements in the middle of the row (eg. Mn) having the widest range of oxidation states. The maximum oxidation state for transition elements up to Mn is equal to the total number of valence electrons available.
V Cr Mn Fe Cu 3d 34s 2 3d 54s 1 3d 54s 2 3d 64s 2 3d104s 1
+2 to +5 +2 to +6 +2 to +7 +2, +3 +1, +2
Oxidation states
Oxidation States of Transition metals
Transition metal ions with a high charge density such as Fe3+ form aqueous solutions that are acidic. This is due to the reaction of the aquo complex ion with water, as shown below.
[Fe(H2O)6]3+ + H2O [Fe(H2O)5OH]2+ + H3O
+
yellow
Note that many complex ions contain twice as many ligands as the charge on the central atom eg [Cu(NH3)4]
2+ or [Ag(NH3)2]+
Zn(OH)2 + 2OH [Zn(OH)4] 2
white ppt colourless soln
Cu(OH)2 + 4NH3 [Cu(NH3)4 ] 2 + + 2OH
light blue ppt dark blue soln
Other complex ions with ammonia are [Zn(NH3)4 ] 2+
and [Ag(NH3)2 ] +.
[Cu(H2O)6 ] 2+ + 4Cl [CuCl4 ]
2 + 6H2O light blue yellow
Oxides/hydroxides of MetalsOxides/hydroxides of Metals The alkali and alkaline metal oxides form basic solutionsThe alkali and alkaline metal oxides form basic solutions
eg Naeg Na22O + HO + H22O 2NaOHO 2NaOH
Transition metal oxides/hydroxides - as TM s increase their Transition metal oxides/hydroxides - as TM s increase their oxidation state oxidation state they become more acidic egthey become more acidic eg
Eg MnEg Mn22OO77 + H + H22O 2HMnOO 2HMnO44
What’s the ON of Mn in MnWhat’s the ON of Mn in Mn22OO77 ? ?
Some transition metal hydoxides are amphoteric (react as acids or bases)Some transition metal hydoxides are amphoteric (react as acids or bases)
Cr(OH)Cr(OH)33 + 3H + 3H++ Cr Cr3+ 3+ + 3H+ 3H22OO
Cr(OH)Cr(OH)33 + OH + OH-- [Cr(OH) [Cr(OH)44]]--
BondingBonding, ,
All noble gases have a stable electron configuration
Ar
Ne; 1s2, 2s2, 2p6
Ar; [Ne] 3s2, 3p6
Only Only ValenceValence Electrons are Electrons are involved in Chemical Bondinginvolved in Chemical Bonding
Lewis Dot Structure = Valence e-s are represented by dots about the elemental symbol
Lewis Symbols
Represent the number of valence electrons as dots
Valence number is the same as the Periodic Table Group No
H
Li Be B C N O F Ne
He
Na; Is2, 2s2, 2p6, 3s1 = [Ne] 3s1
Lewis Structure = Na
For example,
Groups 1 2 3 4 5 6 7 8
Summary of main structures of solidsSummary of main structures of solids
StructureStructureParticles Particles
in the in the SolidSolid
Bonds Bonds between between
the the ParticlesParticles
Boiling Boiling PointPoint
Solubility Solubility in Waterin Water
Electrical Electrical ConductivityConductivity ExamplesExamples
Molecular
small covalent
moleculeslow
Soluble/insoluble depends
on polarity
Giant covalent network
high insoluble
Ionicstrong ionic
bondshigh
sodium chloride,
magnesium oxide
Metallicstrong
metallic bonds
high insoluble
magnesium, iron,
copper, sodium
atoms
very weak forces
Doesn’t conduct In any state methane,
iodine,
water
Strongcovalent bonds
Doesn’t conductin any state
diamond, silicon dioxide
positive and
negative
ions
soluble
conducts whenMolten or in Solution but not when solid
positive ions in a sea of electrons
conducts when
solid and when
molten
PCl Cl
ClPCl Cl
Cl
Rules for Drawing Lewis Structures
• First add up the number of valence electrons from each atom, add one for each negative charge, subtract one for each positive charge.
• The central atom is usually written first in the formula• Complete the octets of atoms bonded to the central atom
(remember that H can only have two electrons)• Place any left over electrons on the central atom, even if
doing so it results in more than an octet• If there are not enough electrons to give the central atom
an octet , try multiple bonds
E.g. 1. PCl3Total Number of valence electrons = 5 + (3 x 7) = 26
PCl Cl
Cl
Draw the following lewis structures
O O x
xxx
xx
Oxygen gas O2
Nitrogen gas N2
H H x
Hydrogen gas H2
N N x x
xxx
Ammonia NH3
N H x
xx
H
H
Draw the following lewis structures
Phosphorus Trichloride PCl3
P Cl x
xx x
xx
x x
Cl x x
x x
x xx
Cl x x
x xx x
C Cl x
xx x
xx
x x
Cl x x
x x
x xx
Cl x x
x xx x
H
Chloromethane CHCl3
(chloroform)
Exceptions to the Octet ruleExceptions to the Octet rule
•An atom can have fewer than 8 e - eg B only needs 6 valence electrons and Be needs 4 valence electrons
•Second row elements never exceed the octet rule. (C, N, O, and F always obey the octet rule)
•Third row elements often satisfy octet rule, but can exceed it by using empty d orbitals
P Cl
Cl
Cl
Cl
Cl
:: :
:
::
::
::: :
: :
: ::
:: :
Elements beyond the second row of the periodic table (Na and beyond) are able to hold more than 8 electrons in their valence shell, due to the presence of d-orbitals.
The maximum number of electrons any atom can have is double its original number (each electron may invite one ‘friend’). Thus S can have a maximum of 12 electrons around it, but B can only have 6.
Draw the Lewis diagram for I3
–.Each I atom has 7 valence electrons. Include one more electron for the minus charge, and the total is 22 electrons.
II I::
Count electrons
Place atoms and charge.
Electrons where there must be bonds.
Make outer atoms happy.
Place rest of electrons on central atom.
All atoms satisfied.
: :::
::
:: : –
The middle I atom can accommodate 10 electrons because of an expandedd subshell
E.g. 2; CHBr3
Total Number of valence electrons = 4 + 1 + (3 x 7) = 26
BrCBr HBr
Exceptions to the Octet Rule in Covalent Bonding
1. Molecules with an odd number of electrons
2. Molecules in which an atom has less than an octet
3. Molecules in which an atom has more than an octet
1. Odd Number of Electrons
NO Number of valence electrons = 11
N O N O Resonace Arrows
NO2 Number of valence electrons = 17
Resonance occurs when more than one valid Lewis structure can be written for a particular molecule (i.e. rearrange electrons)
N OO N OO N OO
O O O OOxygen is a ground state"diradical"
O2
Molecules and atoms which are neutral (contain no formal charge) and with an unpaired electron are called Radicals
Exercise: Draw Lewis diagrams of the following molecules.
CH4, H2S,
CH H
H
H
S
H
H
C OH
HPCl
Cl
Cl C SSC O
H
H
H
H
H2CO, PCl3, CS2, CH3OH
We should be able to reach the same conclusion using the Periodic Table,
Cl is furthest to the right and to the top of the Periodic Table, so is the most electronegative. Se is furthest to the left (‘metallic like’) and towards the bottom. Therefore, difference in electronegativity should be the greatest!
Home work due Tuesday - read unit 4 page 16 complete Q 2,3, 4 and 5 on page 18
StarterStarter
Electronegativity is the ___________ Electronegativity is the ___________ an atom has for _________ in a bond an atom has for _________ in a bond
3. More than an Octet
PCl5
Elements from the third Period and beyond, have ns, np and unfilled nd orbitals which can be used in bonding
P : (Ne) 3s2 3p3 3d0
Number of valence electrons = 5 + (5 x 7) = 40
P
Cl
ClCl
ClCl
10 electrons around the phosphorus
2. Less than an Octet
Includes halides of B, Al and compounds of Be
Group 3A atom only has six electrons around it
B
Cl
Cl Cl
Starter - Draw the lewis diagram of the BCl3 moleculeGive the :
shape bond anglePolarity
Triangular planar
120 o
Non polar
3. More than an Octet
SF4
S : (Ne) 3s2 3p4 3d0
Number of valence electrons = 6 + (4 x 7) = 34
SF
F
F
F
The Larger the central atom, the more atoms you can bond to it – usually small atoms such as F, Cl and O allow central atoms such as P and S to expand their valency.
AlCl3
In the solid form Aluminium chloride is an ionic solid of AlCl3
However, it sublimes at 192 °C to a vapour of Al2Cl6 molecules
AlCl
Cl Cl
ClAl
Cl
Cl
3s2
Al
3p1
[Ne] Ground state
3s2
Al
3p1
[Ne] Promotion of e-
2 Cl electrons can form covalent bond
B2H6
A Lewis structure cannot be written for diborane. This is explained by a three-centre bond – single electron is delocalized over a B-H-B
BH
H H
HB
H
H
COVALENT BONDINGElemental hydrogen exists as a diatomic
molecule H + H H2
• Each hydrogen has one electron in the valence shell.
:H H H H
• However, both hydrogen atoms have the same number of electrons and the same +1 nucleus. The equal pull on the same number of electrons results in a sharing of electron density.
• What are we referring to here Ethiopia ?
ElectronegativityElectronegativity
Electronegativity (EN)Electronegativity (EN) = the ability of a bonding = the ability of a bonding atom to pull electrons from another atomatom to pull electrons from another atom
The higher the EN, the greater the pullThe higher the EN, the greater the pull Fluorine is most electronegative, EN decreases Fluorine is most electronegative, EN decreases
as you move awayas you move away Comparing the EN of two atoms tells you if the Comparing the EN of two atoms tells you if the
electrons are evenly shared (non polar electrons are evenly shared (non polar covalent) or unevenly (polar covalent). covalent) or unevenly (polar covalent).
Electronegativity is defined as the ability of an atom in a molecule to attract electrons to itself
Prof. Linus PaulingNobel Prize for Chemistry 1954Nobel Prize for Peace 1962
Electronegativity is a function of two properties of isolated atoms;The atom’s ionization energy (how strongly an atom holds onto its own electrons)The atom’s electron affinity (how strongly the atom attracts other electrons)
Figure 4.2
Remember that EN(F) is the highest.
Increasing EN
Polar BondsPolar Bonds
When the electronegativities of H and X differ, the resulting bond is polar:
H—X +
The bond has partial ionic character
The three major types of intramolecular bond can be described by the electronegativity difference:
Non-Polar Covalent – Bonds which occur between
atoms with little or no electronegativity difference (less
than 0.5).
Polar Covalent – Bonds which occur between atoms
with a definite electronegativity difference (between 0.5
and 2.0).
Ionic – Bonds which occur between atoms with a large
electronegativity difference (2.0 or greater), where
electron transfer can occur.
E.g. F-F (2.5 – 2.5 = 0) is non-polar covalent
H-F (4.0 – 2.1 = 1.9) is polar covalent
LiF (4.0 – 1.0 = 3.0) is ionic
H F+ -
Dipole moment
Examining the formation of NaClNa + Cl NaCl
IONIC BONDING
Sodium has alow ionization energyit readily loses this electron .When sodium loses the electron, it becomesisoelectronic with Ne.
Na Na+ + e-
Chlorine has a high ionization energy.
When chlorine gains an electron, it becomes isoelectronic with Ar.
:
..
..Cl: e
..
..Cl:
Two viewpoints of NaClTwo viewpoints of NaCl
You must also know and justify the differences betweenIonic solidsMolecular solidsCovalent network solidsmetals
In terms of: boiling point/melting point – ie justify using the forces between particlesConductivitySolubility
structure and bonding
The Effect of an The Effect of an Electric Field on Electric Field on Hydrogen Fluoride Hydrogen Fluoride MoleculesMolecules
Draw the Lewis diagram for NO3–.
Total number of electrons:
5 + 3(6) + 1 = 24.:
All 24 electrons have been distributed. The O atoms have 8 electrons each, which satisfies them, but the N atom only has 6 electrons around it, which is unacceptable.
NO O
O
: :
: :
::
:::
:
:–
All atoms now have an acceptable number of electrons. This is the final Lewis diagram.Move one pair of
electrons to make a double bond.
Bestchoice homework
Particle Properties 3.4 Lewis ex first Then VSEPR :
Problem set 1
Problem set 2
Three Possible Types of BondsThree Possible Types of Bonds
(a) Pure covalent
(b) Polar Covalent
(c) Ionic
Type of BondType of Bond Electron Electron DistributionDistribution
Examples Examples of Bondsof Bonds
Physical Physical PropertiesProperties
IonicIonic(Very different (Very different ENs)ENs)
Transfer to form Transfer to form ions (beyond ions (beyond polar)polar)
LiF, NaClLiF, NaCl Crystalline solids Crystalline solids with high mpswith high mps
Polar CovalentPolar Covalent(Differing ENs)(Differing ENs)
Uneven SharingUneven Sharing HCl, HHCl, H22O, O,
SiClSiCl44, NH, NH
33
gases, liquids or gases, liquids or solids with lower solids with lower mpsmps
Nonpolar Nonpolar CovalentCovalent(similar ENs)(similar ENs)
Even SharingEven Sharing molecular molecular elements, C-H elements, C-H bonds bonds (exception)(exception)
gases, liquids and gases, liquids and solids with very solids with very low mpslow mps
Dipole Moment occurs in any polar covalent bond, because of an unequal sharing of the electron pair between two atoms
E.g. Which of the following bonds is most polar: S-Cl,
S-Br, Se-Cl or Se-Br?S-Cl (3.0 – 2.5) = 0.5S-Br (2.8-2.5) = 0.3Se-Cl (3.0-2.4) = 0.6Se-Br (2.8-2.4) = 0.4
Therefore, Se-Cl is the most polar!
Shapes of moleculesShapes of molecules
Valence-Shell Electron-Pair Repulsion Theory (VSEPR)
In molecules there are 2 types of electron
1. Bonding Pairs2. Non-bonding or lone pairs The combinations of these determine the shape of the molecule The outer pairs of electrons around a covalently bonded atom minimize repulsions between them by moving as far apart as possible
Shapes of molecules
The shape of a molecule is determined by the positions of atoms within that molecule.
The position of those atoms is determined by the arrangement of the electron sets (both bonding and non bonding sets) around the central atom.
Electron sets want to repel each other as much as possible
If there are any non-bonding (‘lone pair’) electrons around the central atom, they will squeeze the bonding pairs (with their attached atoms) closer together.Lone pairs are closer to the central atom than bonding pairs (because they are not shared between two nuclei). They push the bonding pairs slightly closer together than if all pairs were bonding. This is known as lone pair repulsion.
The shape of the molecule depends on: 1. the number of atoms linked to the central atom
2. the total number of electron sets (bonded and non-bonded electron pairs) around the central atom.
NOTE: Multiple electron pairs (i.e. double and triple bonds) are considered to be only one electron set.
The shapes of molecules are determined by the way clouds of electrons are arranged around the central atom in the molecule.
A molecule containing only a single cloud of electrons must be linear.
H—H
Arrangements of electron clouds
Two clouds arrange themselves on opposite sides of the central atom.
The bond angle will be 180°.
O = C = O
Since clouds of electrons are negatively-charged, they repel each other.
Two clouds
Notice that the double bonds in CO2 each act as a single cloud of electrons.
Adding a third cloud of electrons will change the bond angle from 180° to 120°.
All the atoms still lie on a flat plane (like a sheet of paper). The shape is trigonal planar.
Three clouds
When a fourth cloud is added, the previous clouds are pushed downwards.
This shape is tetrahedral.
The bond angle is now 109°.
HH
H
H
C
Four clouds
Remember this number. A circle divided in 4 makes an angle of 90°, but a sphere divided in 4 makes an angle of 109°.
A fifth cloud enters from below, raising the lower 3 clouds back to a flat triangle.
This shape is trigonal bipyramid.
Bond angles around the central triangle are 120°, while the angle between the triangle and the top and bottom atoms is 90°.
P
ClClCl
Cl
Cl
Five clouds
A sixth cloud squeezes around the centre and making all bond angles 90°.
S
FF
FF
F
F
This shape is octahedral.
Six clouds
Three clouds of electrons around central atom:
Trigonal planar
Bent Linear
Bond angle = 120°
Bond angle = 119°
OSO
O SOO
Four clouds of electrons around central atom:
H
HH
HCH
HHN
HH
OH
Cl
Bond angle = 109°
Bond angle = 107°
Bond angle = 105°
Tetrahedral Trigonal pyramid
Bent Linear
The N atom lies above the plane of the H atom.Pyramid with an equilateral triangle as the base.
Trigonal Pyramidal
Five clouds of electronsWhen five clouds of electrons are around the central atom there are two different bond angles — 120° and 90°. Any lone pairs will be positioned around the central triangle first, where they can be 120° away from other clouds.
Trigonal bipyramid
See-saw T-shaped Linear
P F
F
F
FF
S F
F
FF
Cl F
F
F
I
I
I
Six clouds of electrons
Octahedral Square pyramid Square planar
SFFF
F
F
F
BrFFF
F
F
XeFFF
F
Polar Molecules = Molecules with permanent dipole moments
HCl has only one covalent bond (which is polar). Therefore, its dipole moment = H-Cl bond dipole
In a molecule with two or more polar bonds, each bond has a dipole moment contribution = bond dipole
Net dipole moment = vector sum of its bond dipoles
Linear Molecules: CO2 is Non-polar C OO
Because CO2 dipoles are orientated in opposite directions.The dipoles have equal magnitudes and therefore they cancel
Net dipole = 0
The shape of the molecule and
Number of e- sets
Are there polar bonds?
Are polar bonds arranged symmetrically?
Will polar bonds cancel each other?
Will there be a net dipole on the molecule?
ClCl
ClC
Cl The CCl4 molecule is a tetrahedral shape because the 4 bonding electron sets repel each other evenly
The CCl4 molecule has 4 polar C-Cl bonds
These 4 polar C-Cl bonds are arranged symmetrically in the CCl4 molecule
Because the 4 polar C-Cl bonds are arranged symmetrically in the CCl4 molecule they cancel each other and the CCl4 has no net dipole moment and is nonpolar
The shape of the molecule
And number of electron
Sets around central atom
Are there polar bonds?
Are polar bonds arranged symmetrically?
Will polar bonds cancel each other?
Will there be a net dipole on the molecule?
HH
HN
The NH3 molecule has 4 electron sets (3 bonding and 1 non bonding) around the central N atom which repel each other. Because the overall shape of the NH3 molecule is determined by the position of the atoms it is a trigonal pyramid shape
The NH3 molecule has 3 polar N-H bonds
These polar N-H bonds are arranged unsymmetrically in the NH3 molecule
Because the 3 polar N-H bonds are arranged unsymmetrically in the NH3 molecule they do not cancel each other and the NH3 has an overall net dipole moment causing the NH3 to be polar
x x
Intermolecular Forces:
These are generally much weaker than covalent or ionic bonds.
Less energy is thus required to vaporize a liquid or melt a solid.
Boiling points can be used to reflect the strengths of intermolecular forces (the higher the Bpt, the stronger the forces)
Weak Intermolecular ForcesWeak Intermolecular Forces
Consist of:
• Temporary dipole – temporary dipole interactions
•Dipole-dipole interactions
These exist in Polar Molecules
•The permanent dipole interacts with other permanent dipoles to cause attraction.
•exist between all polar molecules,
•The strength of the attraction depends on the polarity of the molecule.
Permanent dipolesPermanent dipoles
Electrons are in constant motion.
Electrons can be, in an instant, arranged in such a way they have a dipole. (Instantaneous dipole)
•The temporary dipole interacts with other temporary dipoles to cause attraction.
• exist between all molecules (polar and non polar)
•is the only attractive force between non polar atoms or molecules,
Temporary dipolesTemporary dipoles
Intermolecular ForcesIntermolecular Forces•Boiling point is dependant on the intermolecular forces
•Polar molecules have higher b.p. than nonpolar molecules.
Dipole - Dipole bondingDipole - Dipole bonding
Hydrogen bondingHydrogen bondingHydrogen bonding is an extreme form of dipole-
dipole attraction. Examples include: H2O, NH3, HF
Hydrogen Bonding :
the attractive force between hydrogen in a polar bond (particularly H-F, H-O, H-N bond) and an unshared electron pair on a nearby relatively small electronegative atom or ion
Very polar bond in H-F forms H bonds.The other hydrogen halides don’t form hydrogen bonds, since H-X bond is less polar. As well as that, their lone pairs are at higher energy levels. That makes the lone pairs bigger, and so they don't carry such an intensely concentrated negative charge for the hydrogens to be attracted to.
Hydrogen Bonding & Water
H-bonding causes the lower density of ice in comparison to liquid water, this means ice floats on water.
In most substances the molecules in the solid are more densely packed than in the liquid. A given mass of ice occupies a greater volume than that of liquid water.
This is because of an ordered open H-bonding arrangement in the solid (ice) in comparison to continual forming & breaking H-bonds as a liquid.
•Use your knowledge of bonding to compare the different boiling points of :Ionic/covalent network/metallic/and molecular substances
Test Info
electron configuration of atoms and ions of thefirst 36 elements (using s,p,d notation)
periodic trends in atomic radius, ionisationenergy and electronegativity
comparison of atomic and ionic radii
Lewis diagrams of molecules and ionsShape and polarity
Weaker Intermolecular Forces
Ion-Dipole Forces
An ion-dipole force is an attractive force that results from the electrostatic attraction between an ion and a neutral molecule that has a dipole. Most commonly found in solutions. Especially important for solutions of ionic compounds in polar liquids. A positive ion (cation) attracts the partially negative end of a neutral polar molecule. A negative ion (anion) attracts the partially positive end of a neutral polar molecule.
Ion-dipole attractions become stronger as either the charge on the ion increases, or as the magnitude of the dipole of the polar molecule increases.
Dipole-dipole Attractive Forces
A dipole-dipole force exists between neutral polar molecules Polar molecules attract one another when the partial positive charge on one
molecule is near the partial negative charge on the other molecule The polar molecules must be in close proximity for the dipole-dipole forces to
be significant Dipole-dipole forces are characteristically weaker than ion-dipole forces
Dipole-dipole forces increase with an increase in the polarity of the molecule
Boiling points increase for polar molecules of similar mass, but increasing dipole:
SubstanceMolecular
Mass (amu)Dipole
moment, u (D)Boiling Point
(°K)
Propane 44 0.1 231
Dimethyl ether
46 1.3 248
Methyl chloride
50 2.0 249
Acetaldehyde
44 2.7 294
Acetonitrile 41 3.9 355
London Dispersion Forces – significant only when molecules are close to each other
Prof. Fritz London
Due to electron repulsion, a temporary dipole on one atom can induce a similar dipole on a neighboring atom
Group 4A hydrides
Groups 4, 5, 6A hydrides
Van der Waals forces are made of dipole-dipole and London dispersion forces
Periodic Table TrendsPeriodic Table Trends
The Structure The Structure of Lithium of Lithium FluorideFluoride
Formal ChargeFormal Charge
Formal charge = (# valence e in neutral atom
# “assigned” valence e in molecule)
“assigned” elone pair e
bonded pair e2
1
VSEPR ModelVSEPR Model(“valence shell electron pair repulsion”)(“valence shell electron pair repulsion”)
Write Lewis structure Write Lewis structure Count Count ee pairs around atoms pairs around atoms
(single bonds, multiple bonds, and lone pairs (single bonds, multiple bonds, and lone pairs all count as 1 pair)all count as 1 pair)
Arrange bonds to minimize repulsion Arrange bonds to minimize repulsion between between ee pairs pairs
Lone pairs have greater repulsion than Lone pairs have greater repulsion than bonding pairsbonding pairs
Molecular Molecular Structure Structure of Methaneof Methane
The Molecular Structure of NHThe Molecular Structure of NH33
The Molecular Structure of HThe Molecular Structure of H22OO
The Bond Angles in the CHThe Bond Angles in the CH44, NH, NH33, and , and
HH22O MoleculesO Molecules
EElectron lectron PairsPairs
Bonding Pair
Lone pair
Possible Possible Electron Pair Electron Pair Arrangements Arrangements for XeFfor XeF44
Three Possible Arrangements of Three Possible Arrangements of the Electron Pairs in the Ithe Electron Pairs in the I33
-- Ion Ion
TThe Molecular he Molecular Structure of Structure of MethanolMethanol
Sizes of Sizes of Ions are Ions are Related Related to to Positions Positions of the of the Elements Elements in the in the Periodic Periodic TableTable
CompoundCompound Bond Length Bond Length ((Å)Å)
Electronegativity Electronegativity DifferenceDifference
Dipole Dipole Moment (D)Moment (D)
H-FH-F 0.920.92 1.91.9 1.821.82
H-ClH-Cl 1.271.27 0.90.9 1.081.08
H-BrH-Br 1.411.41 0.70.7 0.820.82
H-IH-I 1.611.61 0.40.4 0.440.44
Electronegativity difference decreases as bond length increases
Dipole Moment: µ = Qr
Dipole moment is defined as the magnitude of charge (Q) multiplied by the distance between the charges; units are D (Debye) = 3.36 x 1030 C.m
Prof. Peter DebyeNoble Prize 1936
When proton & electron 100 pm apart, the dipole moment is 4.80 D
4.8 D is a key reference value! It represents a pure charge of +1 and -1, which are 100 pm (100pm = 1Å) apart. The bond is said to be 100% ionic!
H-F; µ = 1.82 D (measured) bond length = 0.92 pmIf 100% ionic,µ = 92/100 (4.8 D) = 4.42 D% ionic = 1.82/4.42 x 100 = 41 % ionic
H-Cl; µ = 1.08 D (measured) bond length = 1.27 pmIf 100% ionic,µ = 127/100 (4.8 D) = 6.10 D% ionic = 1.08/6.10 x 100 = 18 % ionic
H-Br; µ = 0.82 D (measured) bond length = 1.41 pmIf 100% ionic,µ = 141/100 (4.8 D) = 6.77 D% ionic = 0.82/6.77 x 100 = 12 % ionic
Symmetrical molecules (e.g. CCl4, CH4) are non-polar. The four dipoles
are of equal magnitude and neutralize one another at the center of a
tetrahedron
Non-symmetrical molecules (e.g. CHCl3, CO(CH3)2, H2O) are Polar.
The dipoles are not all equal or in opposite directions (partial charges and
bond lengths are all different in C-Cl, C-H, C=O, C-H)
(H2O is a bent molecule not linear, see later notes)
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