Models of the Atom Section 13.1 The story of how the atomic theory has evolved over time….
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Transcript of Models of the Atom Section 13.1 The story of how the atomic theory has evolved over time….
Models of the AtomSection 13.1
The story of how the atomic
theory has evolved over time….
John Dalton
The atom is a solid indivisible mass. He had 4 key ideas: Page 107
All elements are composed of tiny indivisibleparticles called the atom.
Atoms of the same element are identical. Atoms of different elements are different. Atoms combine chemically with one another in
simple whole-number ratios. During chemical reactions, atoms are separated,
joined, or rearranged. Atoms are never creatednor destroyed.
JJ Thomson
Plum-pudding model. Sometimes called the Chocolate Chip Cookie
Model The atoms has negatively charged
electrons stuck into a lump of positively
charged material, like chocolate chips
stuck in a cookie dough. Did not address protons and neutrons.
Ernest Rutherford
Discovered the nucleus. Showed that most of an atom’s mass is
concentrated in a small, positively
charged region called the nucleus. Electrons resided on the outside. Did not address how electrons were
arranged.
Neils Bohr
Electrons are arranged on concentric
circular paths, or orbits around the
nucleus. Solar system model or planetary model. Gave us the idea of definite energy
levels.
Quantum Mechanical Model –Our Currently Accepted Model Erwin Schrodinger
Primarily a mathematical model using quantum
mechanics It addresses “probabilities” of finding an electron
at any instant in an area called “electron clouds”. Introduced the ideas of Principal Energy Levels
and Sublevels of energies. The electron clouds take certain shapes,
represented by the s,p,d,f subatomic orbitals.
Principal Energy Levels
Just like the Bohr model, the QuantumMechanical Model designates energy levelsof electrons by means of principalquantum numbers called (n).
Principal Energy Levels refers to amajor region where electrons are mostlikely to be found.
They are assigned values in order ofincreasing energy: n=1, n=2, n=3, etc.
Sublevels
Within each principal energy level, theelectrons occupy energy sublevels.
The number of sublevels within eachprincipal energy level is the same as
the principal quantum number. How many sublevels does the 4th
principal energy level have?
Atomic Orbitals
The regions in which electrons are likely
to be found are called atomic orbitals. Letters denote the atomic orbitals
S-shape orbitals are spherical P-shape orbitals are hour-glass shapes D-shape orbitals have clover-leaf shapes
Draw an example of each into yournotes.
Exploring further…
The lowest principal energy level (n=1)
has only one sublevel, called 1s. The second principal energy level (n=2)
has 2 sublevels, the 2s and 2p. The 2p is
higher in energy and consists of 3 p
orbitals. Let’s show an easy way to remember this
order of filling electrons…
The Electron Pyramid
The s orbitals have 1 spatial orientation,
therefore can hold 2 electrons The p orbitals have 3 spatial orientations,
therefore can hold 6 electrons The d orbitals have 5 spatial orientations,
therefore can hold 10 electrons The f orbitals have 7 spatial orientations,
therefore can hold 14 electrons.
Electrons Fill following 3 simplerules Aufbau principle: Electrons enter the
lowest energy level first. Pauli Exclusion Principle: An atomic
orbital may describe at most 2 electrons,both spinning in opposite directions.
Hund’s Rule: When electrons occupyorbitals of equal energy, one electronenters each orbital until all the orbitalscontain one electron with parallel spins.
Classifying Elements by Electron Configuration
Of the three major subatomic particles, the electron plays the most significant role in determining the physical and chemical properties of an element
The arrangement of elements in the periodic table depends on these properties
Elements can be classified into four categories according to their electron configurations
1. The noble gases2. The representative elements3. The transition metals4. The inner transition metals
The Noble Gases
These are elements in which the outermost s and p sublevels are filled
Belong to Group 0 (Group 8A)
Configurations
Helium 1s2
Neon 1s22s22p6
Argon 1s22s22p63s23p6
Krypton 1s22s22p63s23p64s23d104p6
The Representative Elements
In these elements, the outermost s or p sublevel is only partially filled
Usually called the Group A elements and include the noble gases in some definitions
ConfigurationsLithium 1s22s1
Sodium 1s22s22p63s1
Potassium1s22s22p63s23p64s1
Carbon 1s22s22p2
Silicon 1s22s22p63s23p2
Germanium 1s22s22p63s23p64s23d104p2
The Transition Metals
These are metallic elements in which the outermost s sublevel and nearby d levels contain electrons
Called the Group B elements
ConfigurationsZinc1s22s22p63s23p64s23d10
Tungsten1s22s22p63s23p64s23d104p65s24d105p66s24f145d4
Lead1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p2
The Inner Transition Metals
These are metallic elements in which the outermost s sublevel and nearby f sublevel generally contain electrons
Characterized by the filling of f orbitals
ConfigurationsUranium1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f4
Curium1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f8
S1 S2
S2 p1 p2 p3 p4 p5 p6
d1 d2 d3 d4 d5 d6 d7 d8 d9 d1
0
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14
“D” Block
“F” Block
“P” Block
“S” B
lock
Period
1
2
3
4
5
6
7
6
7Period
Practice
Write the electron configurations for the following elements:
Nitrogen1s22s22p3
Nickel1s22s22p63s23p64s23d8
Vanadium1s22s22p63s23p64s23d3
Practice
What are the symbols for all the elements that have the following outer configurations?
S2 S2P5 S2D2
Helium (He) Fluorine (F) Titanium (Ti)Beryllium (Be) Chlorine (Cl) Zirconium (Zr)Magnesium (Mg) Bromine (Br) Hafnium (Hf)Calcium (Ca) Iodine (I) Rutherfordium (Rf)Strontium (Sr) Astatine (At)Barium (Ba)Radium (Ra)
Exceptional ElectronConfigurations Chromium and Copper have exceptional
electron configurations. They fill their d sublevel completely,
leaving their 4s partially filled. Much more stable this way! Write them correctly into your
notepacks…Cr: 1s22s22p63s23p63d54s1
Cu: 1s22s22p63s23p63d104s1
Physics and the QuantumMechanical Model This section studies the electron as a
property of light. Electrons travel as waves and are made
of particles of light called photons According to the wave model, light
consists of ELECTROMAGNETIC
RADIATION.
Electromagnetic Spectrum
This form of energy includes Gamma rays X-rays Ultraviolet rays Visible light Infrared rays Radar FM TV Shortwave AM
Electromagnetic Spectrum
Every element emits light when it isexcited by the passage of electric
discharge through its gas or vapor. The atoms first absorb energy, then
lose the energy as they emit light.
Electromagnetic Spectrum
Electrons are said to move from theirGROUND STATE (lowest energy level)
to and EXCITED STATE (higher energy
level). When the electron falls back to its lower
energy, it emits a PHOTON of energy,
and can be seen in the visible spectrum.
Electromagnetic Spectrum
Passing the light emitted by an elementthrough a prism gives the ATOMIC
EMISSION SPECTRUM of the element. Because each atom has a unique
electron arrangement, each atom emits
a unique wavelength during this
process. This wavelength falls within
the visible spectrum.
Kernel Structures
The kernel is a structure used toshorten an electron configuration.
A kernel is an inert gas symbol inbrackets that stands in place of all of
the filled orbitals contained in the inert
gas. Examples
Section 14.1
Classification of theElements By Electron Configuration
Classifying Elements byElectron Configuration Of the three major subatomic particles,
the ELECTRON plays the most
significant role in determining the
properties of an element. The arrangement of elements in the
PERIODIC TABLE depends on these
properties.
Elements can be classified into 4categories: The Noble Gases :
These are elements in which the
outermost s and p sublevels are filled.
Write for Helium, Neon, Argon, Krypton The representative elements:
In these elements, the outermost s
and p sublevel is only partially filled.
Write for Lithium, Sodium, Potassium,
Carbon, Silicon, Germanium
Elements can be classified into 4categories: The transition metals:
These are metallic elements in whichthe outermost s sublevel and nearby d
sublevel contain electrons.
Write for Zinc and Zirconium. The inner transition metals:
These are metallic elements in which
the outermost s sublevel and nearby f
sublevel generally contain electrons.
14.2 Periodic Trends
Atomic radius – ½the distance
between the nuclei
of two like atoms in
a diatomic molecule.
GroupTrends
Atomic size generally increases asyou go down a group on the
periodic table. Adding additional energy levels!
PeriodicTrends
Atomic size generally decrease as youmove from left to right across a period.
Same energy level -increasing nuclear charge pulls electronscloser to nucleus.
Ionization Energy
An ion – a charged atom that resultsfrom either losing or gaining an
electron. Ionization Energy – The energy
required to overcome the attraction of
the nuclear charge and remove an
electron from a gaseous atom. (The ease of losing an electron and
forming a +1 charge)
Ionization Energy
First ionization energy – the energyneeded to remove the first electron
from an atom. Second ionization energy – the energy
needed to remove the second electron
from an atom, etc.
Ionization Energy
Group Trends: The first ionizationenergy generally decreases as you
move down a group on the periodic
table. The size of the atoms increases, so the
outermost electron is farther from the
nucleus and will be more easily
removed.
Ionization Energy
Periodic Trends – For the representativeelements, the first ionization energy
generally increases as you move from
left to right across a period. Increasing nuclear charge makes it
more difficult to remove an electron.
Ionic Size
The atoms of METALLIC elements havelow ionization energies. They form
POSITIVE ions easily. By contrast, the atoms of
NONMETALLIC elements readily form
NEGATIVE ions.
Trends in Ionic Size
Positive ions are always smaller thanthe neutral atoms from which theyform. They lose their outer shell electrons
Negative ions are always larger thanthe neutral atoms from which theyform. This is because the effective nuclear
attraction is less for an increased numberof electrons.
Trends in Electronegativity
Electronegativity – the tendency for theatoms of the element to attract electrons
when they are chemically combined with
atoms of another element. Electronegativity generally DECREASES as
you go down a group. As you go across a period from left to right,
the electronegativity of the representative
elements INCREASES.
Electronegativity
The electronegativity of cesium, theleast electronegative element is 0.7
The electronegativity of fluorine, themost electronegative element, is 4.0
Electronegativity values help predict thetype of bonding that can exist between
atoms in compounds, either IONIC OR
COVALENT bonds.
Summary of Periodic Trends
Using page 406, create a summary ofperiodic trends into your notes.