Download Protons, Neutrons, Electrons

Protons, Neutrons, Electrons
We know that atoms are made of protons, electrons, and neutrons. The atomic number of an element is defined as the number of protons an atom of that
element has in its nucleus. For a neutral atom, this will also be equal to the number of electrons the atom has.
Ion and Isotope. Both have something the same, something different. Both start with the letter “i". Don’t confuse them!
Isotopes are atoms of the same element that have identical numbers of protons but different numbers of neutrons. Ions are made when an atom gains or lose
electrons. The mass number of an atom is the number of protons plus the number of neutrons in the atoms’s nucleus.
The mass number is not found on the periodic table; it must be either given or be calculated. The mass number is used to identify the different isotopes of an
element. For example, there are 2 different isotopes for Vanadium-50 and Vanadium-51. We can write this in different ways:
Vanadium - 50 or 5023V or 50V
51
Vanadium - 51 or 51
V
23V or
Here is a completely-written identification for an atom of Vanadium-51. Note the location of the mass number, the atomic number, and where the ion charge
any) are written. You must remember what each of these numbers means, so that you can fully describe the isotope!
Mass number
51
23
V

Atomic number
Ion charge (if none, it’s an
atom, not an ion!
• Protons: look it up on the periodic table to find its atomic number, which must equal the number of protons.
• Neutrons: The number of neutrons is never written you must calculate it! Since mass # = protons + neutrons, and atomic # = protons.
See above, 51-23 = 28 neutrons.
• Electrons: The charge of the ion identifies the number of electrons compared to the number of protons. In a neutral atom, electrons = protons. When an atom
loses electrons, it becomes positively charged (more protons than electrons). You may find this equation helpful:
Charge = (number of protons) – (number of electrons)
KEY THOUGHT: Unless you are shown it’s an ion you may assume that each line represents a neutral atom.
Number of
Protons
Number of
Neutrons
Number of
Electrons

Isotope
Symbol
Atomic
number
Mass
Number
Isotope name
23
23
51
Vanadium-51
51
23
50
23
V
a)
23
28
b)
23
27
23
23
50
Vanadium-50
c)
23
28
20
23
51
Vanadium-51
d)
47
62
47
47
109
Silver-109
109 Ag
47
e)
38
50
38
38
88
Strontium-88
88 Sr
38
48
62
46
48
110
Cadium-110
110
48
35
46
35
35
81
Bromine-81
81 Br
35
35
44
36
35
79
Bromine-79
79 Br
35
i)
22
24
18
22
46
Titanium-46
46 Ti+4
22
j)
88
135
88
88
223
Radium-223
223 Ra
88
V
+3
f)
g)
h)




51
23
V
Cd +2
1-
182 W2+
k)
74
108
72
74
182
Tungsten-182
74
8
8
8
8
16
Oxygen- 16
16 O
8
m) 8
9
8
8
17
Oxygen- 17
17 O
8
18 O
8
l)
n)
8
10
8
8
18
Oxygen-18
p)
53
74
54
53
127
Iodide - 127
127 –1
I