Atomic Structure
History
B.C. – Democritus proposed all matter was
made up of small particles called atoms
 Atomic numbers were assigned to elements by
Henry Moseley
 1913- Niels Bohr described the planetary model of
the atom
 400
Planetary model
The Shell Model
 The
more accurate model puts a cloud around the
nucleus and electrons move about in shells
 Each shell can hold so many electrons
 Little energy in the most inner shell so only 2
electrons can be found there.
 The farther you get from the nucleus, the more
electrons a shell can hold
The atoms makeup
 This
shell model of a hydrogen atom or lead atom
is made up of the same general parts.
 A nucleus made up of protons (1 in Hydrogen and
82 in Lead) and neutrons (usually the same amount
as the protons)
 Floating around the nucleus are electrons
Mass of Subatomic Particles
Particle
Charge Mass compared Actual Mass
to electron
Electron
Proton
Neutron
Negative
Positive
Neutral
1
1836
1841
9.11x10-31
1.673x10-27
1.675x10-27
Charges
 The
three subatomic particles as they are called
have different charges
 Protons- (+)
 Neutrons- no charge
 Electrons- (-)

Atomic Mass
 The
mass of an atom is equal to the number of
protons and neutrons found in the nucleus
 If an atom of carbon has 6 protons and 6 neutrons,
its mass is 12
Atomic Number
 The
atomic number found above the chemical
symbol is equal to the number of protons the atom
has
 An atom with 19 protons has to be potassium (K)
Chemical Names
 Why
is Co different from CO?
 Co is Cobalt
 CO is carbon monoxide
 Be sure to use upper and lower case properly
Isotopes
 Atoms
of the same element that have different
numbers of neutrons are called isotopes
 Hydrogen can have 0, 1, or 2 neutrons in it’s
nucleus
Misc. Facts
 Hydrogen
is the most abundant element. It makes
up almost 90% of all atoms. As well it was the 1st
element to exist
 Fused hydrogen atoms formed inside stars and this
created the other elements
 Most atoms formed when the universe began and
are constantly being recycled
 Atoms that make up ‘you’ are billions of years old
Names w/ 1 letter that begins
name
Names w/ 2 letters and both
letters are start of name
Carbon
Neon
Names w/ 2 letters and 1st
letter starts and second is
heard later in name
Magnesium
Symbol has nothing to do
with name
Sodium
Chapter Review (class work)
 Try
to complete #5, 6, and 7.
Protons have a positive charge
A.
B.
True
False
C-12 is a radioactive isotope used in
carbon dating fossils
A.
B.
True
False
The charge of a neutron is
A.
B.
negative
No charge
The number of electrons that can fit in
the 1st shell is
A.
B.
C.
8
2
18
The electron has more mass than the
proton and neutron
A.
B.
Yes
No
The atomic number of carbon is
A.
B.
C.
D.
12.01115
12
6
C
The element symbol of helium is
A.
B.
C.
D.
H
2
He
Helium
The mass number of C-14 is 14
A.
B.
True
False
Play-doh Lab
Partner up
 Create a 3 dimensional model of an atom using play-doh
and beads. It must be the shell model
 Your atom must have an atomic number between 6 and
12.
 On a separate sheet draw your atom and label the
following: Protons, neutrons, electrons, nucleus, electron
cloud, any and all shells
 Write down the name, atomic number, atomic mass, and
symbol
