Atomic Structure
Applied Chemistry
Modern Atomic Theory

Three subatomic particles:


protons (p+), neutrons (n0), and electrons (e-)
Particles found IN the nucleus:
protons and neutrons
 These are called nucleons


Particles found OUTSIDE the nucleus:

electrons in the electron cloud
Relative Mass and Charge
of Subatomic Particles
Particle
Mass (amu)
Charge
Proton
1
+1
Neutron
1
0
Electron
0
-1
Note: amu = atomic mass unit (1/12 the mass of a carbon atom)
Modern Atomic Theory

Atomic Number = # of p+1
ALWAYS equals the number of protons (p+)
 Identifies the element


Mass Number = # of p+ + # of n0


Equals the number of protons plus neutrons
Neutral atoms: # of p+ = # of e
In neutral atoms, the # of protons equals the #
of electrons
Boxes on the Periodic Table
1
Atomic Number
1.008
Atomic Mass
H
Hydrogen
Element Name
Element Symbol
For Hydrogen with a Mass Number = 1
# of protons = 1
# of neutrons = 0
# of electrons = 1
Why aren’t atomic masses
whole numbers?
Neutral atoms of an element have the same
number of protons, but the number of
neutrons can vary.
 Isotopes: Atoms of an element with the same
number of protons, but different number of
neutrons. (Atoms of the same element with
different masses.)
Atomic Mass is really the average atomic mass
of all the isotopes. Mass number and
Atomic Mass are NOT the same!!!

Isotopes of Hydrogen
Isotopic Name – (2 parts)
Sodium - 23
Element
(Name or
symbol can
be used)
Mass number
Example
Element
Protons
Electrons
Neutrons
Carbon-12
6
6
6
Oxygen -16
8
8
8
Fluorine -19
9
9
10
How are isotopes
expressed?

Isotopic Symbol – shows symbol
for an element, the mass number,
and the atomic number.
Mass Number
20
Ne
10
Atomic Number
Example of Isotopic Symbol
20
Ne
10
Element is Neon
Mass number is 20
Atomic Number is 10
# of protons is 10
# of neutrons is 10
# of electrons is 10
Example Chart
Isotopic
Symbol
Isotopic
Name
Atomic
Number
Mass
Number
# of
protons
3
7
3
4
3
17
37
17
20
17
56
137
56
81
56
7
3
Li
Lithium-7
37
17
Cl
Chlorine-37
137
56
Ba
Barium-137
# of
# of
neutrons electrons
Are atoms always neutral?
A.
When atoms have a charge, they are
called ions.
B.
This charge is due to an UNEQUAL
number of protons and electrons.
C.
Charge = protons - electrons
Ions (cont.)
D.
Metals tend to lose electrons and have a
positive charge.

Positive ions are called cations.

The name of the cation is the same name
as the element followed by the word ion.
Ex. Sodium ion
Ions (cont.)
E.
Nonmetals tend to gain electrons and
have a negative charge.

Negative ions are called anions.

The name of an anion uses the element
name but the ending is changed to ide.
Example: chloride
CATION
Ca†ion
“cat”ion
ANION
anion
“ant”ion
Example of Ions
1.
Fluorine-19 becomes an ion by
gaining 1 electron.
2.
As a result, it will have 9 protons
and 10 electrons.
IONS
Isotopic
Symbol
19
9
24
12
F
1
Mg
32
16
59
28
S
2
2
Ni
2
Proton
Neutron
Electron
Mass #
Charge
Cation
or Anion
9
10
10
19
-1
A
12
12
10
24
+2
C
16
16
18
32
-2
A
28
31
26
59
+2
C
Where are the electrons in
the electron cloud?
a)
b)
+
e-
nucleus
c)
Electrons are in energy
levels.
The outermost electrons
are called valence
electrons. They are in the
highest energy level.
The electrons in their
lowest energy level are in
the ground state.
Where are the electrons in
the electron cloud?
d)
e)
+
e-
absorb
energy
f)
g)
Electrons can absorb energy
often from heat or electricity.
When electrons absorb
energy, they become excited.
They jump up to a higher
energy level.
They are not stable at the
higher energy level.
This is called the excited
state.
Where are the electrons in
the electron cloud?
h)
emitted
energy
+
ei)
Because electrons are not
stable, the electrons fall
back to a lower energy
level, called the ground
state.
It releases (or emits)
energy, in the form of
electromagnetic radiation
when it returns to the
ground state.
Hydrogen Atom
electrons fall to n = 1 and
give off ultraviolet light.
electrons fall to n = 2 and
give off visible light.
electrons fall to n = 3 and
give off infrared light.