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Chemistry 75 25
for Secondary Schools 35 × + 37 ×
100 100
2625 + 925
=
100
3550
= = 35.5
100
FOR ONLINE READING ONLY
(b) Neon has three isotopes:
20 Ne(90.5%), 21 Ne(0.3%), 22 Ne(9.2%)
10 10 10
The relative atomic mass of neon is:
90.5 0.3 9.2
20 × + 21 × + 22 ×
100 100 100
1810 6 3 202 4.+ + .
= 100
2018 7.
= 100
= 20.187
It can be noted that for both chlorine and neon, the R.A.M. is very close to
35
the mass number of the isotope with the highest abundance, namely 17 Cl and
20 Ne, respectively.
10
Chapter summary
1. An atom is the smallest particle of an element. It can only be split or
destroyed by nuclear reactions.
2. There are three major sub-atomic particles, namely:
(a) protons (positively charged),
(b) neutrons (neutral), and
(c) electrons (negatively charged).
3. Protons and neutrons are located in the nucleus of an atom while electrons
are found in the shells or energy levels around the nucleus.
20 Student’s Book Form Two
01/08/2025 11:20:52
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 20 01/08/2025 11:20:52
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 20
