The Electron (e-)
I. In the Atom:
A. Is negatively charged
B. Held to the positively charged nucleus (p+ and no) by the
Electromagnetic Force
C. A lepton – nonbaryonic matter since has no quarks
D. Created when a neutron decays
E. Determines whether there is bonding between atoms and
what type of bonds these may be
F. If an atom loses or gains e- - it becomes an ion
1. If lost e-; then the p+ are the majority in the atom
and it gets a positive charge: called a cation
2. If gains e-; then p+ in minority and atom is negatively
charged and called anion
If it loses IQ – it’s a
G. In a stable, neutral atom – the number of protons equals
the number of electrons (and is the same as number of
neutrons)
1. Atomic Number = # p+
2. Stable Atom: #p+ = #e- = #no
3. Atomic Mass – Atomic Number = # no
II. Models
A. Plum Pudding Model – J.J. Thompson
B. Planetary Model – Neils Bohr
1. Used to explain atom
C. e- Cloud Model – Schrodinger
1. Heisenberg Uncertainty Principle: Can’t know exactly
where the electron is in the orbit around nucleus so
must use probability to determine its position
III. Energy Levels
A. Electrons orbit in one of seven levels around nucleus
1. The further from the nucleus – the more energy
B. If it is in its regular level – it’s in its ground state
C. If the atom gains energy, in the form of a photon, then
the e- will jump up a level to its excited state
1. When the energy is given up in the form of a photon,
then the electron drops back down to its ground state
2. The wavelength (color) of the light seen is related to
the energy level(s) changed by the electron(s)
IV. Electron Levels and More
A. Energy levels (n) range from 1 to 7
B. Each energy level will have one to four sublevels or orbitals
Symbol
Name
Shape
Max. # e-
s
sharp
spherical
2
p (x, y, z)
principle
figure 8
6 (2 each x, y, z)
d
diffuse
four leaf clover
10
f
fundamental 6 leaf clover
14
(4 horizontal and
2 vertical)
g
theory only 8 leaf clover
(starts w/
element 119)
18
C. Electron Spin
1. Electrons in same suborbital must have opposite
spins – one up and one down
a. Maximum of 2 e- per suborbital
2. Pauli Exclusion Principle
a. No 2 e- in same atom can have same
quantum numbers – spin, etc.
D. Aufbau Principle
1. Electrons fill up suborbitals and energy levels from
the bottom (lowest energy) to top (highest energy)
2. Part of the electron configuration system
3. Aufbau Notation – Shows last set of electrons
2p
Energy
Level
5
# Electrons (Valence)
Shape
E. Hund’s Rule
1. “Share the Cookie Rule”– each suborbital must get
at least one electron before it can get a second
F. Valence Electrons – the outer most shell of electrons
1. Octet Rule – atoms want up to 8 valence electrons
a. Atom’s will either give up or “steal” electrons
from other atoms to get to this octet
b. This determines whether an atom will form
a negative or positive ion
c. Lewis Dot Diagrams
# e-‘s in Valence Shell
Valence Energy
Level (n)
Suborbital Shapes
the Level Contains
Max. # e-
1
s
2
2
s, p
2, 6 = 8
3
s, p, d
2, 6, 10 = 18
4
s, p, d
2, 6, 10 = 18
5
s, p, d
2, 6, 10 = 18
6
s, p, d, f
2, 6, 10, 14 = 32
7
s, p, d, f
2, 6, 10, 14 = 32
V. Electron Configuration
A. 7 energy levels (n)
1. Each energy level or orbital can have up to 4 suborbitals
a. s, p, d, f
b. Remember maximum number of e- allowed in each
B. Diagramming
1. Aufbau Principle – fill energy levels from lowest to highest
2. Pauli Exclusion Principle – no two e- can have same spin, etc.
3. Hund’s Rule – each suborbital gets one e- before a second
(Share the Cookies Rule)
4. Octet Rule – complete valence shell (*)
C. Systems
1. Aufbau Diagram
a. Long and short forms
2. Lewis Dot Diagrams
3. Noble Gas Configuration
VI. Ions and Isotopes
A. Ion
1. Number of p+ is unequal to #e2. Atom has lost or gained electrons
a. If gained – a negative sign with a number after symbol
b. If lost – a positive sign with a number
c. Positive Ion – cation – means protons outnumber electrons
and atom will have an overall positive charge
d. Negative Ion – anion – electrons outnumber protons leading
to a negative charge on the atom
B. Isotope – unequal number of neutrons and protons
1. Has no effect on the atom’s charge
2. Only affects atom’s mass
3. Take atomic mass – atomic number to find # no
Noble Gas Electron Configuration
Use the [Noble Gas] as a short cut to listing the electrons
for an element
Use:
He for Period 2
Ne for Period 3
Ar for Period 4
Kr for Period 5
Xe for Period 6
Rn for Period 7
Example: Cu [Ar] 4s13d10 where the last listings are the
valence electrons for Cu
Electron Diagram – Aufbau Principle
x
y
z
7p
5f
x
y
z
6p
5d
x
y
z
5p
x
y
z
4p
Orbital Filling Sequence ↑
Increasing Energy Level ↑
Orbital Shapes: s, p, d, f
x
y
z
3p
x
y
z
2p
[ex.  1s2]
Start ↑
Notes:
Pauli Exclusion Principle:
Hund’s Rule:
one
two elections each. (Share the Cookie Rule).
Bohr Model: 7 principle energy levels (n = 1 through 7) of electrons; K, L, M, N. Maximum electron capacity per energy level is 2n2
Orbitals (ml): For any l there are 2I + 1 orbitals in that level; deals w/ angular momentum along the x, y, and z axes and orientation of electron cloud
Sublevels / Orbital Type (l): s (spherical); p (perpendicular); d (diffuse); f (fundamental); n – 1 = # sublevels
Spins (ms): ↑ +1/2; ↓ - ½
Octect Rule: Completed valence electron energy level