The arrangement of the electrons in an atom
3 marks · EasyThe table shows the atomic numbers of several elements.
| Element | Atomic number |
|---|---|
| Lithium | 3 |
| Silicon | 14 |
| Argon | 18 |
Which element is in Group 1?
Which element is found in Period 3?
Explain how the atomic number of an element helps you decide its position in the Periodic Table.
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(a) Lithium
(b) Silicon and Argon
(c) The atomic number tells you how many protons and electrons the atom has, which determines how the electrons are arranged in shells. This arrangement shows the element’s group and period in the Periodic Table.
Common mistakes: Incorrect group/period for elements; Vague explanations for atomic number
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Marking points
B1 (a) · 1 mark · Identifies Lithium as the Group 1 element.
B1 (b) · 1 mark · Identifies Silicon and Argon as elements in Period 3.
M1 (c) · 1 mark · Explains how atomic number links to position in the Periodic Table.
Worked solution
a) Lithium (atomic number 3) has 1 electron in the outer shell: Group 1.
b) Silicon (atomic number 14, configuration 2,8,4) and Argon (18, configuration 2,8,8) are both in Period 3 (3 electron shells).
c) The atomic number tells us the number of protons and electrons, which determine the electronic structure. This structure shows the group (outer electrons) and period (number of shells).