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Electronic structure for AQA GCSE Chemistry

Electronic structure

This page covers the following topics:

1. Electronic structure
2. Dot and cross diagrams

The electronic structure is the way in which electrons are arranged in an atom. Electrons in atom are arranged in shells (or energy levels) surrounding the nucleus. For many atoms, the electrons in an atom occupy the shell nearest the nucleus first, until it is full.

The first shell can contain 2 electrons. For elements up to and including calcium, the second and third shells can contain 8 electrons. Their electronic structure can be written as a numbers x, y, z, where x represents the number of electrons in the first shell, y in the second and z in the third.

Each electron shell corresponds to an energy level. For example, electrons that are in the second electron shell are in the second energy level.

Electronic structure

Dot and cross diagrams are a simple way of visualising electrons in the orbitals of atoms and compounds. The electrons in the outer shell are known as valence electrons, they usually participate in reactions. Information about how many electrons are in each shell can be taken directly from their electronic structure.

Dot and cross diagrams

1

Draw a cross diagram for an atom of magnesium.

The electrons in an atom occupy the shell nearest the nucleus first, until it is full. The first shell can contain 2 electrons. For elements up to and including calcium, the second and third shells can contain 8 electrons.

The atom has 12 electrons as its atomic number is 12.
Allocating these 12 electrons into the first few electron shells gives 2, 8, 2.

image

Draw a cross diagram for an atom of magnesium.

2

What is the electronic structure of this element?

The atom has 2 electrons in the 1st shell and 2 electrons in the 2nd shell.
Thus, the electronic structure of this element is 2, 2.

2, 2

What is the electronic structure of this element?

3

What is the electronic structure of an element with an atomic number of 16?

The electrons in an atom occupy the shell nearest the nucleus first, until it is full. The first shell can contain 2 electrons. For elements up to and including calcium, the second and third shells can contain 8 electrons.

The element has 16 electrons as its atomic number is 16.
Allocating these 16 electrons into the first few electron shells gives 2, 8, 6.

2, 8, 6

What is the electronic structure of an element with an atomic number of 16?

4

Which element is this dot diagram representing?

Electronic structure 2, 1 means that the element has 2 + 1 = 3 electrons.
The number of electrons and the atomic number match for atoms.
Thus, the atomic number of the element is 3 and it is lithium.

lithium

Which element is this dot diagram representing?

5

What is the electronic structure of aluminium, that has 13 protons?

The electrons in an atom occupy the shell nearest the nucleus first, until it is full. The first shell can contain 2 electrons. For elements up to and including calcium, the second and third shells can contain 8 electrons.

Aluminium has 13 electrons as it has 13 protons.
Allocating these 13 electrons into the first few electron shells gives 2, 8, 3.

2, 8, 3

What is the electronic structure of aluminium, that has 13 protons?

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