Atoms
the smallest particle of an element
that retains its identity in a
chemical reaction.
- electrically neutral
- spherical
- positively charged nucleus
surrounded by one or more
negatively charged electrons
Early Ideas of the Atom
Democritus: believed that atoms were
indivisible and indestructible
Dalton: first organized atomic theory based
on the scientific method.
Experiments
Thomson: discovered the electron using
cathode ray tubes. Created the plumpudding model.
Millikan: calculated the mass of the
electron using the oil droplet experiment.
Rutherford: discovered the nucleus using
the gold foil experiment. Disproved the
plum-pudding model.
Honors Chemistry 2.A
Electrons in the Atom
The Bohr Model
• An electron is found only
in specific circular paths, or
orbits, around the nucleus
• Each possible electron
orbit in Bohr’s model has a
fixed energy
• The fixed energies an
electron can have are
called energy levels.
an electron can jump
from one energy level to
another
• the electrons in an atom
cannot be between
energy levels
• an electron must gain or
lose energy to move from
one energy level to
another (quantum)
• the higher an electron is
on the energy ladder, the
farther it is from the
nucleus.
The Quantum Mechanical
Model
the quantum mechanical
model does not involve an
exact path the electron takes
around the nucleus
• determines the allowed
energies an electron can have
and how likely it is to find the
electron in various locations
around the nucleus
• based on probability
Atomic Orbitals
•A region of space in which there is a high probability of
finding an electron.
• Solving Schrodinger’s equation gives the energies an
electron can have
• The energy levels are labeled by quantum numbers (n)
• Each energy sublevel corresponds to an orbital of a
different shape, which describes where the electron is
likely to be found.
n=1 has 1 sublevel (1s)
n=2 has 2 sublevels (1s 2p)
n=3 has 3 sublevels (1s 2p 3d)
n=4 has 4 sublevels (1s 2p 3d 4f)
Electron Configurations
Electrons and the nucleus interact to
make the MOST STABLE arrangement
Electron Configurations are the ways in
which electrons are arranged in different
orbitals around the nucleus
The following rules tell you how to find
the electron configurations of atoms...
The Aufbau
Principle •The s sublevel is always the
Each box represents an
orbital
Pauli Exclusion
Principle and
Hund’s Rule
an atomic orbital
may describe at
most two
electrons, each
with opposite spin
direction
•electrons occupy
orbitals of the
same energy in a
way that makes
the number of
electrons with the
same spin
direction as large
as possible
The principle quantum energy level
only holds that many sub-levels.
Principal Energy
Level # of sub-levels
sub-levels
n=1
n=2
n=3
n=4
1
2
3
4
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
The number of electrons in
each sub-level.
sub-level
# of electrons in each sub-level
s
2
p
6
d
10
f
14
Maximum number of electrons in each
energy level.
Principal
Energy
Level (n)
sub-levels
electrons
total number
of electrons
1
2
3
4
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
2
2+6
2 + 6 +10
2 + 6 + 10 +
14
2
8
18
32
The orbitals in each sub-level.
sub# of
# of
level electrons in orbitals
s
p
d
f
each sublevel
2
6
10
14
1
3
5
7
Names of each orbital
s
pz px py
dz2 dxz dyz dxy dx2-y2
fz3 fxz2 fyz2 fxyz fz(x2-y2) fx(x2-3y2) fy(3x2-y2)
Electron Configuration “Rules”
1.Identify how many electrons are in the atom.
2.There is a maximum of 2 electrons per orbital.
Total electrons: s=2, p=6, d=10, f=14
3.Electrons do not pair up within an energy sub-level
until each orbital already has 1 electron.
4.Place electrons in the orbitals (lowest energy first)
until the superscripts add up to the total number of
electrons.
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6
6s2 4f14 5d10 6p6 7s2 5f14...
Periodic Table Shortcut
PERIOD # = # of shells / energy levels
Electron Configurations of
Ions
Na:
Na+:
Exceptional EC’s
Chromium: Cr
What we would predict:
What it actually is:
1s2 2s2 2p6 3s2 3p6 4s1 3d5
Copper: Cu
What we would predict:
What it actually is:
1s2 2s2 2p6 3s2 3p6 4s1 3d10
The 3d suborbital
is more stable
when either half
filled OR
completely filled.
These transfers
lower the overall
energy.
Valence Electrons
The electrons in the highest occupied energy
level of an atom
Using electron configuration: add the s electrons
and the p electrons only
example: P: 1s2 2s2 2p6 3s2 3p3
2+3= 5 valence e-
Using group number: GROUP # = # valence eThese are usually the only electrons involved in
chemical bonds
The Periodic Table of Elements
Periods (row) & Groups (columns)
Metals: good conductors (heat & electricity), ductile,
malleable, shiny
Metalloids: properties are similar to, and in between,
metals and nonmetals
Nonmetals: poor conductors & brittle. Physical
properties differ between nonmetals (hard to generalize).
Trends in the Periodic Table:
Atomic Size
Trends in the Periodic Table:
Ionization Energy
Ionization Energy: the energy required to remove an
electron from an atom and overcome the electron+proton
attraction. Related to ionic charge.
Trends in the Periodic Table:
Ionic Size
Cations (+) -> lost e- -> smaller
Anions (-) -> gained e- -> larger
Trends in the Periodic Table:
Electronegativity
Electronegativity: the ability of an atom to attract
electrons when the element is part of a compound.
Can be used to
predict the type
of bond that will
form
The most
electronegative
element is F