Chemistry 112
Chapter 4 Notes: Sub-Atomic Particles and Isotopes
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There are 3 major subatomic particles (inside the atom):
subatomic
mass
charge location
particle
(a.m.u.)
proton
1
1+
nucleus
neutron
1
0
nucleus
electron
0
1e cloud
atomic number (Z) - the number of protons in an atom (Z=p). Every element has its own unique
number of protons in the nucleus of all its atoms. Note: always a whole number – a count of p’s.
mass number (A) - the number of protons and neutrons in an atom (A=p+n). The number of
neutrons in an atom can vary. Note: always a whole number – a count of p’s & n’s.
atomic mass - the average mass of all the atoms in a sample of an element. Note: always a
number with decimals, since it is an average.
isotope - a particular atom of an element, having the same number of protons but a different or
unique number of neutrons (same atomic number, different mass number; same element,
different atomic mass).
Example:
chlorine consists of 2 different atoms – isotopes:
chlorine-35 (17 p, 18 n, 17 e)
chlorine-37 (17 p, 20 n, 17 e)
Note the average atom mass of chlorine is 35.45 – indicating that the element chlorine is
made up of more of isotope 35 than isotope 37.
standard atomic notation - the method for showing specific isotopes, using subscripts and
superscripts. Examples: chlorine-35 and chlorine-37 in standard atomic notation would be:
4.
Complete the following table.
atom/ion
symbol
atomic
number (Z)
Z=p
mass
number (A)
A=p+n
protons
p (+)
electrons
e (-)
neutrons
n
charge
(compare
p & e)
F
9
19
9
9
10
0
Ca
20
41
20
18
21
+2
Fe
26
56
26
23
30
+3
Br
35
80
35
36
45
-1
C
6
12
6
6
6
0
C
6
14
6
2
8
+4
Zn
30
64
30
28
34
+2
Zn
30
72
30
30
42
0