Page 28 - Chemistry_Form_2

Chemistry
for Secondary Schools

4. The arrangement of electrons in different shells of an atom is known as
electronic arrangement or electronic configuration.
5. Each shell can contain only a certain number of electrons, with the maximum
being 2n , where n is the position of the shell from the nucleus.
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6. For any neutral atom of an element:

Number of protons = atomic number
Number of electrons = number of protons = atomic number
Number of neutrons = mass number – atomic number

7. Isotopes are atoms of the same element with the same number of protons
but different number of neutrons.

8. The relative atomic mass of an element is the average mass of one atom of

the element relative to 1 the mass of one carbon-12 atom.
12 th

Revision exercise 1

Choose the correct answer for Questions 1−8. For other questions, provide the
answers as per the demands indicated.

1. Which description corresponds to a proton?

(a) Relative mass = 1, charge = + 1
(b) Relative mass = 1, charge = 0

(c) Relative mass = 1 , charge = –1
1840
(d) Relative mass = 4, charge = +2.

2. What are nucleons?
(a) Neutrons and electrons
(b) Neutrons and protons

(c) Electrons and protons
(d) Protons, neutrons and electrons

3. Which atomic property is the basis for the use of carbon-14 in archaeology
for dating ancient objects?

Student’s Book Form Two 21

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CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 21