Number of Protons
Atomic Number
Number of Protons + Neutrons
Mass Number
12 is the mass number.
C-12 or carbon-12
Left Superscript = mass number
12C
6
Left Subscript = atomic number
12C
6
35
80Br
35
Atomic Number = ?
20
20Ne
10
Mass Number = ?
238
238U
92
Mass Number = ?
27
27Al
13
Mass Number = ?
20
40Ca
20
Atomic Number = ?
9
19F
9
Atomic Number = ?
Mass Number = 235
Atomic Number = 92 (Look up!)
U-235
Mass Number? Atomic Number?
Mass Number = 14
Atomic Number = 6 (Look up!)
Number of neutrons = 14 - 6 = 8
C-14
How many neutrons?
Atoms of the same element
with a different # of neutrons
Isotope
Atoms with the same atomic #
but different mass #
Isotope
Charge = +1, mass = 1 amu,
location = inside nucleus
Characteristics of Proton
Charge = 0, mass = 1 amu,
location = inside nucleus
Characteristics of Neutron
Charge = -1, mass = 1/1836 amu or
0.0005 amu, location = outside
nucleus
Characteristics of Electron
An atom that has gained or lost
electrons & so carries charge
Ion
Protons & Neutrons
Nucleons
Smallest bit of an element that
retains the properties of the
element.
atom
Electrically neutral.
# of protons = # of electrons.
atom
# protons - # electrons
Charge
Mass number – atomic number
# of neutrons
8
14C
6
# of neutrons = ?
5
9Be
4
# of neutrons = ?
22
40Ar
18
# of neutrons = ?
8
15N
7
# of neutrons = ?
Right superscript = charge
2+
24Mg
12
10 electrons
2+
24Mg
12
# of electrons?
36 electrons
86Rb
1+
37
# of electrons?
53 electrons
127Te
52
1-
# of electrons?
18 electrons
32S
16
2-
# of electrons?
9 protons, 11 neutrons, 10 electrons
20F
9
-
# of protons, neutrons, electrons?
Positive ion: atom lost electrons
Cation
Negative ion: atom gained
electrons
Anion
Weighted avg. of masses of
naturally occurring isotopes of an
element.
Avg. Atomic Mass
Avg. atomic mass =
.75(35) + .25(37) = 35.5 amu
2 isotopes of Cl: 75% Cl-35 & 25% Cl-37.
Calculate avg. atomic mass.
Billiard Ball Model
Dalton’s Model
Plum Pudding Model
Thomson’s Model
- +
+ -+ +
-+ -
Nuclear Model
Rutherford’s Model
-
+
-
Rutherford’s Experiment
Source: http://www.dlt.ncssm.edu/TIGER/chem1.htm#atomic
1) Most of the alpha particles went straight
through.  Most of the atom is empty
space.
2) Some of the alpha particles were
deflected back.  The nucleus was tiny,
but contained most of the mass of the
atom.
Rutherford’s Experiment:
Results
Planetary Model
Bohr’s Model
Modern or Quantum Mechanical
Model
Schrodinger’s Model
Source:
http://www.dlt.ncssm.edu/TIGER/chem1.htm
#atomic
Electron treated as a wave.
Never know exactly where it is.
Modern Model (Schrodinger or
Quantum Mechanical Model)
Ground state configurations
found in reference tables.
Cannot be predicted.
Bohr Configuration
2 electrons in energy level 1
8 electrons in energy level 2
1 electron in energy level 3
Bohr Configuration of Na = 2-8-1
+11
Bohr Diagram of Na
Electron(s) in outermost
orbit or shell
Valence Electron(s)
Nucleus + all innershell
electrons: Everything
except the valence electrons
Kernel
Electrons are restricted to specific orbits or
shells or principle energy levels.
Each shell holds a specific # of electrons.
Each shell has a specific energy & radius.
Energy of electron must match energy of shell.
Bohr Model
Maximum Capacity of Bohr Levels
Shell #
Max # of electrons
1
2
2
8
3
18
4
32
n
2n2
Bohr model
Every electron is in the lowest available
orbit.
Ground State
Ground state
configuration of Cl
2-8-7
Ground state
configuration of O
2-6
2-8-18-8
Ground state configuration
of Kr?
Shell #
Principle Energy Level?
Bohr model
An electron has absorbed heat, light, or
electrical energy and moved to a higher
energy level.
Unstable. Returns to ground state quickly
by emitting a photon.
Excited State
An excited state of O
2-5-1
An excited state of Li
2-0-1
Spectrum produced by holding a prism in
sunlight. Contains light at every
wavelength.
Rainbow
Continuous Spectrum
Visible light produced by electrons in atom returning
to ground state: light of only a few wavelengths is
present.
Each element has a unique bright line spectrum. Used
to identify elements.
Wavelengths of bright lines correspond to difference
between energy levels.
Bright Line Spectrum
Source: http://www.dlt.ncssm.edu/TIGER/chem1.htm#atomic
E3
Excited state
E2
h
E1
Ground state
Absorbtion of Energy
h
E3
Excited state
E2
E1
Ground state
Emission of Energy
Modern Model
Region of space that holds 2 electrons.
Has a specific energy. Shapes vary.
Orbital
Represents an electron dropping to a lower
energy level, releasing energy in the
process.
E2
E1