Post on 12-Jan-2016
atomic number
Background on the Periodic Table
Dmitri Mendeleev: given creditfor Periodic Table (~1870)
--
--
organized Table byincreasing atomic mass left spaces and predictedproperties of undiscoveredelements
Henry Moseley: put elements inorder of increasing____________.
Mendeleev
Moseley
Describing the Periodic Table
periodic law: the properties of elements repeat every so often
period:
group (family):
horizontal row; there are 7
vertical column; there are 18 18
1716151413
129 101187654
1
3
21234
67
5
computer chips
metalloids (semimetals): “stair” between metalsand nonmetals
properties: in-between those of metalsand nonmetals; “semiconductors”
Regions of the Table (cont.)
(B, Si, Ge, As, Sb, Te, Po)
Si and Ge
computer chips
metals
nonmetals
Same number of valence e– =
Li Na
In any group, the element BELOW has one moreoccupied energy level than does the element ABOVE.
Li Na
similar properties
1s2 2s1 1s2 2s2 2p6 3s1
The period that an element is in is the same as theenergy level that its valence electrons are in.
Li Na
v.e– in 2nd E.L. v.e– in 3rd E.L.
in 3rd periodin 2nd period
alkali metals:
alkaline earth metals:
halogens:
noble gases:
contain f orbitals
lanthanides:
coinage metals:
transition elements:
main block (representative) elements:
group 1 (except H); 1+ charge;very reactive
group 2; 2+ charge;less reactive than
alkalisgroup 17; 1– charge; very reactive
group 18; no charge; unreactive
elements 58–71
actinides: elements 90–103
group 11
groups 3–12; variable charges
groups 1, 2, 13–18
alkaline earth metals
halogensnoble gaseslanthanides
alkali metals actinidescoinage metalstransition elements
main block elementsmetalloids
hydrogenmore nonmetals
more metals
Periodic Trends
We will be studying four trends across the Periodic Table.
Atomic radii: the distance from the nucleus to the farthest e-.
Ionic radii: the distance from the nucleus to the farthest e- in that element’s ion.
Electronegativity: the propensity for an element to attract e- from another atom. It’s ability to bond.
Ionization energy:: the amount of energy required to pull one e- away from an element; to remove one electron.
Trends
Atomic radius
Ionization energy
Electronegativity
Periodic Trend
Electron shielding: the inner e- block some of the pull from the nucleus so the valence e- don’t feel as much.
- --
-
--
-++++
+++
Feels the force of 7 p+
Feels the force of 5 p+
Effective nuclear charge is how many p+ are pulling on that e-
shielding effect: kernel e– “shield” valence e–
from attractive force of the nucleus
Li v.e–
K v.e–
-- caused by kernel and valence e–
repelling each other
As we go , shielding effect increases...
tougher to remove
easierto
remove
Shielding Effect
Kernel electrons block the attractive force of the nucleus from the valence electrons
+nucleus
Valence
Electrons--
-
-
Electron Shield“kernel”electrons
Periodicity
there are trends in properties of elements
-- left-right AND up-down trends
atomic radius: the size of a neutral atom
add a new energylevel each time
WHY?
…increases as we go
…decreases as we go
WHY?
coulombic attraction: attraction between (+) and (–)
it has to do with…
Coulombic attraction depends on…
2– 2+
2+ 2– 1–
2–
1+
2+
amount of charge distance between charges
+ + – –
H
He
+ –
+ – + –
As we go , more Coulombic
attraction, No new energy level, more
pull = smaller size
Decreasing Atomic Size Across a Period
As the attraction between the (+) nucleus and the (–) valence electrons , the atomic size .
From left to right, size decreases because there is an increase in nuclear charge and Effective Nuclear Charge (# protons – # core electrons).
Each valence electron is pulled by the full Effective Nuclear Charge.
Li Be B1s22s1 1s22s2 1s22s22p1
Li Be B
Atomic Radii
Li
Na
K
Rb
Cs
ClSPSiAl
BrSeAsGeGa
ITeSbSnIn
Tl Pb Bi
Mg
Ca
Sr
Ba
Be FONCB
1.52 1.11
1.86 1.60
2.31 1.97
2.44 2.15
2.62 2.17
0.88 0.77 0.70 0.66 0.64
1.43 1.17 1.10 1.04 0.99
1.22 1.22 1.21 1.17 1.14
1.62 1.40 1.41 1.37 1.33
1.71 1.75 1.46
IA IIA IIIA IVA VA VIA VIIA
=1 Angstrom
Relative Size of Atoms
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 350
ionic radius:
cations anions
Ca atom Ca2+ ion Cl atom Cl1– ion
the size of an ion
20 p+
20 e–
20 p+
18 e–
17 p+
17 e–
17 p+
18 e–
Ca Ca2+ Cl Cl1–
cations are smaller anions are larger
Formation of Cation - Cation is Smaller than Parent.
11p+
sodium atomNa
e-
loss of one valence
electron
e-
e-
e-
e-e-
e-
e-
e- e-
e-
sodium ionNa+
11p+e-
e-
e-
e-e-
e-
e-
e-
e-
e-e-
Formation of Anion - Anion is Bigger than Parent Atom
17p+
chlorine atomCl
e-
e-
e-
e-
e-e-
e-
e-
e- e-
e-
e-
e-
e-
e-
e-
e-
e-
gain of one valence
electron
chloride ionCl1-
17p+e-
e-
e-
e-e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
e-
Sizes of ions: electron repulsion
Valence electrons repel each other.
9
+
• When an atom becomes an anion (adds an electron to its valence shell) the repulsion between valence electrons increases without changing effective nuclear charge.
• Thus, F– is larger than F
Fluorine atomF
1s22s22p5
9+-
--
-
--
--
-
F1-
1s22s22p6
+1e+1e-- 9+-
--
-
--
--
-
-
Fluorine ionFluoride ion
Trends in Atomic and Ionic Size
152
186
227
Li
Na
K
60
Li+
95
Na+
133
K+
e
e
eF-
136
Cl-
181
Br-
195
F
Cl
Br
64
99
114
e
e
e
Metals NonmetalsGroup 1
Al
143
50
eee
Group 13 Group 17
Cations are smaller than parent atomsAnions are larger than parent atoms
Al3+
IA IIA IIIA IVA VA VIA VIIA
0.60 0.31
0.95 0.65
1.33 0.99
1.48 1.13
1.69 1.35
1.71 1.40 1.36
0.50 1.84 1.81
0.62 1.98 1.85
0.81 2.21 2.16
0.95
Li1+ Be2+
Na1+ Mg2+
Cl1-
N3- O2- F1-
S2-
Se2- Br1-
Te2- I1-
Al3+
Ga3+
In3+
Tl3+
Ca2+K1+
Sr2+Rb1+
Cs1+ Ba2+
Li
Na
K
Rb
Cs
ClSPSiAl
BrSeAsGeGa
ITeSbSnIn
Tl Pb Bi
Mg
Ca
Sr
Ba
1.52 1.11
1.86 1.60
2.31 1.97
2.44 2.15
2.62 2.17
0.88 0.77 0.70 0.66 0.64
1.43 1.17 1.10 1.04 0.99
1.22 1.22 1.21 1.17 1.14
1.62 1.40 1.41 1.37 1.33
1.71 1.75 1.46
Be B C N O F
= 1 Angstrom
AtomicRadii
IonicRadii
Cations: smaller than parent atoms
Anions: LARGERthan parent atoms
Ionization Energies
• Energy is required to remove an electron from an atom to form a cation.
• Ionization energy () is the amount of energy needed to remove an electron from the gaseous atom E in its ground state:
• Larger values of mean that the electron is more tightly bound to the atom and is harder to remove.
• Units for ionization energies are kilojoules/mole (kJ/mol) or electron volts (eV) - 1 eV = 96.49 kJ/mol.
Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.
Electronegativity
The ability of anatom in a compound to attract sharedelectrons to itself.
Linus Pauling1901 - 1994
Electronegativity:
It is a measure of the ability of an atom to attract additional electron to it.
Group: Electronegativity decreases down a group because the outer energy level is further away from the nucleus which results in a weaker nuclear charge available to attract additional electrons or less ability for an atom to attract electrons to it.
Electronegativity (Cont.):
Period: Electronegativity increases moving across a period from left to right because the atoms in the same period have the same number of energy levels but the number of protons increase as you go from atom to atom across a period increasing the attraction between the nucleus and the outer energy level resulting in a greater ability for atoms to attract electrons to it.
electronegativity:
Linus Pauling quantifiedthe electronegativity scale.
the tendency fora bonded atom toattract e– to itself
As we go , electronegativity…
As we go , electronegativity…
decreases.
increases.
electronegativity increases