Grade 9 Applied Science - Chemistry
Atoms – The Inside Story
There are three types of SUBATOMIC PARTICLES:
 PROTON – positively charged with a mass of 1 and located in
the nucleus
 NEUTRON – neutral or no charge with a mass of 1 and
located in the nucleus
 ELECTRON – negatively charged (-) with virtually no mass
(measured as zero) and moving rapidly in SHELLS or ORBITS
in the space around the nucleus.
NOTE: The number of protons in the nucleus is called the ATOMIC NUMBER. The
Atomic Number determines the identity of the atom.

The element Potassium (K) has an Atomic Number of 19. Thus, K has 19
protons.
NOTE: The number of protons MUST EQUAL the number of electrons in an element.

If K has 19 protons, K also has 19 electrons.
If the number of positively-charge protons equals the number of negatively-charged
electrons, the OVERALL CHARGE OF THE ATOM IS ZERO.
Fill in Table 1
Element
Lithium
Number of
Protons
Total
Positive
Charge
Number of
Electrons
Total
Negative
Charge
Net Charge
of the Atom
3
3+
3
3-
0
Sodium
Neon
Carbon
The other number is ATOMIC MASS. It is the SUM of the protons and the neutrons
Number of Protons + Number of Neutrons = Atomic Mass
Fill in Table 2
Element
Element
Symbol
Number of
Protons
Number of
Neutrons
Atomic Mass
Lithium
Li
3
4
7
Oxygen
O
Silicon
Si
Phosphorus
P
Practice – Fill in Table 3 using the ideas above
Element
Element
Symbol
Atomic
Number
Carbon
C
6
Number of
Protons
Number of
Electrons
36
24
Ag
28
108
80
80
79
U
84
47
Hg
Nickel
Atomic
Mass
6
Kr
Silver
Number of
Neutrons
118
28
59
92
238
DRAWING ATOMS – Bohr-Rutherford Diagrams
Danish physicist Niles Bohr suggested that there was a regular pattern in the position
and motion of electrons. He stated:
 Electrons move in definite ORBITS around the nucleus
 The orbits are located at certain distances from the nucleus
 Electrons cannot coexist between orbits, although electrons can move up and
down between orbits
 The MAXIMUM NUMBER of electrons in the first three orbits are 2, 8 and 8
 Electrons are more stable when they are closer to the nucleus
This is a Bohr-Rutherford diagram for Sodium (Na).



Na has 11 protons. They are located in the
nucleus by the notation 11p
Na has an Atomic Mass of 23. Thus, Na has 12
neutrons (23 -11). The neutrons are in the
nucleus. They are shown as 12n
Na has 11 electrons. They are found in orbits
around the nucleus. Two electrons are found in
Orbit #1, eight electrons are in Orbit #1 and one
electron in Orbit #3.
Practice – Using your Periodic Table, draw Bohr-Rutherford Diagrams for…
17Cl
20Ca
3Li
7N
16S
13Al
Answers
Table 1
Element
Number of
Protons
Total
Positive
Charge
Number of
Electrons
Total
Negative
Charge
Net Charge
of the Atom
Lithium
3
3+
3
3-
0
Sodium
11
11+
11
11-
0
Neon
10
10+
10
10-
0
Carbon
6
6+
6
6-
0
Element
Symbol
Number of
Protons
Number of
Neutrons
Atomic Mass
Lithium
Li
3
4
7
Oxygen
O
8
8
16
Silicon
Si
14
14
28
Phosphorus
P
15
16
31
Table 2
Element
Table 3
Element
Element
Symbol
Atomic
Number
Number of
Protons
Number of
Electrons
Number of
Neutrons
Atomic
Mass
Carbon
C
6
6
6
6
12
Krypton
Kr
36
36
36
48
84
Chromium
Cr
24
24
24
28
52
Silver
Ag
47
47
47
61
108
Mercury
Hg
80
80
80
121
201
Gold
Au
79
79
79
118
197
Nickel
Ni
28
28
28
31
59
Uranium
U
92
92
92
146
238