Atomic number and mass
number – Extend
CC3b.3
1
Where is most of the mass of an atom found in the atom? Explain your answer.
2
Atoms can be described in a shorthand way such as
3
72
32 Ge.
a
Write the atomic number and mass number of this atom.
b
How many protons, neutrons and electrons are in this atom?
Copy and complete these formulae, which can be used in calculations involving the structure of atoms.
a
atomic number =
b
mass number =
c
number of electrons =
d
number of neutrons =
e
number of protons =
E1 Formulae can be written to connect the atomic number, mass number, and numbers of protons, electrons
and neutrons in atoms. For example: atomic number = number of protons. Write formulae that connect
the other four numbers.
4
Explain why an atom has an overall neutral charge.
5
Work out what numbers and symbols should be written (a to n) to complete the table below.
Element
6
Mass
number
Number of ...
protons
neutrons
electrons
arsenic
33
75
a
b
c
silver
d
e
47
61
47
scandium
21
f
g
25
h
hydrogen
1
1
i
j
k
sodium
l
23
m
12
n
a One of the atoms in the table in question 2 has twice the mass of another atom in the table. Identify
these two elements, stating which is which.
b
7
Atomic
number
Explain your answer to part a.
Two atoms are described in the table.
a
Write down these two atoms in the form
A
of Z symbol.
b
Explain why these two atoms can be
described as being atoms of the same
element even though they do not have
the same structure.
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Number of ...
Element
protons
neutrons
chlorine
17
18
17
chlorine
17
20
17
4
electrons