Atoms and molecules

1. Chapter 8
Model of Matter —
Atoms and Molecules
Worksheet 8.1
Pg 87-90
Graded: Challenge Yourself
Q1, 2, 5, 6, 7, 8 and 9 [12 marks]

2. Secure your basics
Explanation:
The atoms are of 2 different sizes, implying that the
substance is made up of 2 type of atoms.

3. Explanation:
Protons and neutrons have the same relative mass of 1.
Electrons have negligible mass.

4. Explanation:
Option B is not true as in a molecule of ammonia, there are
1 nitrogen atom and 3 hydrogen atoms.

5. Explanation:
Option A is not true as different compounds have different
mass numbers (different chemical formulae).
Option B is not true as HClO3 does not contain carbon atoms.
Option D is not true as the compounds have different
chemical formulae (different number of electrons).

6. Explanation:
If the diagram shows 1 type of atom, it is an element.
If the diagram shows 2 or more type of atoms chemically
bonded, it is a compound.
Mixture Element
Mixture
Compound

7. Map It Out
Start from here.
The only sub-atomic particle
that has no charge is the
neutron.

8. ChallengeYourself
H2O / CO2 / CO / HCl /
NH3 / NO2 / NO / SO2
H2O / CO2 / NO2 / SO2
Accept any other suitable answers
[1]
[1]

9. electron
proton
neutron
Electrons are outside the nucleus.In the nucleus,
since the number of electrons is equal to the number
of protons, B has to be proton and C is neutron.
[2]

10. Lithium has an atomic number of 3 (number of protons) and
mass number of 7 (3 protons + 4 neutrons). [1]

11. In an atom, the number of protons (positively
charged) is equal to the number of electrons
(negatively charged). [1]
Hence, the positive charge of the protons is balanced
by the negative charge of the electrons. [1]

12. No, atoms do not have a unique number of neutrons. [1]

13. Yes, each atom has a unique number of protons. [1]
Atoms are arranged in ascending order of atomic
number (number of protons) in the PeriodicTable.

14. An atom of gold (Au) has 79 protons, 79 electrons and
118 neutrons. [2]

15. •
Use PeriodicTable and search for
atomic number 53 and 80 number of protons = number of electrons
number of neutrons = mass number  atomic number
Atomic number is the number of protons
[1]