SNC2D – Chemistry: Chemical Reactions
Subatomic Particles, Atomic Notation, Counting Atoms
(p. 184-185)
Subatomic Particles:
Atoms are composed of 3 basic subatomic particles:
Particle Name and Symbol
Charge
Location in Atom
Protons (p+)
Positive
In the nucleus
Neutrons (n°)
Neutral
In the nucleus
Electrons (e-)
Negative
Moving around the nucleus
Atomic Notation:
Atomic notation is a concise, convenient way to give information about the atom of an element.
General Format
A
Z
Example with Sodium
X – element symbol
X
A – atomic mass (# protons
+ # neutrons)
23
11
Na – symbol for sodium
Na
Z – atomic number (#
protons)
Atomic mass = 23 (#
protons + # neutrons =
23)
Atomic number = 11 (#
protons = 11)
Examples and Practice:
# protons = 17
35
17
Cl
39
19
108
47
# electrons = 17
# neutrons = 35 – 17 = 18
# protons = 19
K
# electrons = 1919
# neutrons = 2039 – 19 =
20
# protons = 47
Ag
# electrons = 47
# neutrons = 61
56
26
19
9
# protons = 26
Fe
# electrons = 26
# neutrons = 56 – 26 =
30
# protons = 99
F
# electrons = 9 9
# neutrons = 10
SNC2D – Chemistry: Chemical Reactions
Counting Atoms:
A molecule’s chemical formula specifies the types of atoms (elements) that make up the
molecule, as well as the number of atoms of each element.
Type of Atom
Potassium (K)
Sulfur (S)
Oxygen (O)
K2SO4
# of Atoms
2
1
4
Type of Atom
# of Atoms
Nitrogen (N)
2
Hydrogen (H)
8
Oxygen (O)
3
Carbon (C)
1
----------------------------------------------------------------------------------------------
(NH4)2CO3
Practice Exercises:
a. Identify the elements which have the following numbers of protons in the nuclei of their
atoms:
8 __oxygen_______
30 __zinc_________
38 __strontium____
82 __lead_________
b. Write the atomic notation for each of the following atoms:
14
a) An atom with 8 protons and 6 neutrons: ______ 8 O ________________
12
b) An atom with 6 protons and 6 neutrons: ______ 6 C _______________
1
c) An atom with 1 proton and 0 neutrons: _______ 1 H ______________
80
d) An atom with 45 neutrons and 35 electrons: ___ 35 Br ____________
c. Name the element that:
a) has an atomic number of 7 and a mass number of 14: __nitrogen___________
b) has 10 protons and a mass number of 20: __neon_________________
c) has 17 electrons and 17 protons: __chlorine_______________
d) has 30 neutrons and a mass number of 56: ___iron________________