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Electronic structure for AQA A-level Chemistry

Electronic structure

This page covers the following topics:

1. Electronic structure
2. Electronic configuration

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

Electron shells in an atom are made up of atomic orbitals, which are regions around the nucleus that can hold up to two electrons, with opposite spins. There are s, p and d orbitals, each with a different shape. Here are all available orbitals for the first 4 energy levels:
1st โ†’ 1s
2nd โ†’ 2s 2p
3rd โ†’ 3s 3p 3d
4th โ†’ 4s 4p 4d 4f

The other 3 energy levels have a similar pattern to the 4th energy level. The fact that particular shells exist in a level doesnโ€™t mean that they will be filled for an element in a corresponding period. For example, d-orbitals that are found in 3rd level will only start to be filled for 4th period elements as there are no d-block elements in period 3. s orbital exits alone, p orbitals in groups of 3, d in groups of 5 and f in groups of 7. Each orbital can fit 2 electrons.

Shells fill up in order s โ†’ p โ†’ d โ†’ f by going through each element from hydrogen to the element of interest and assigning them to corresponding orbitals. An electron configuration is written by using the aforementioned templates for the energy levels and by including superscript letters representing the number of electrons in each orbital. For example, calcium would have an electronic configuration of 1sยฒ 2sยฒ 2pโถ 3sยฒ 3pโถ 4sยฒ.

Electronic configuration

1

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?

2

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?

3

Which element has the electronic configuration of 1sยฒ 2sยฒ 2pโถ 3sยฒ 3pยฒ?

This element has 2 + 2 + 6 + 2 + 2 = 14 electrons.
For atoms the number of electrons and the atomic number is the same.
The atomic number of the element is 14 and it is silicon.

silicon

Which element has the electronic configuration of 1sยฒ 2sยฒ 2pโถ 3sยฒ 3pยฒ?

4

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?

5

Which element has the electronic structure 2, 6?

Electronic structure 2, 6 means that the element has 2 + 6 = 8 electrons.
The number of electrons and the atomic number match for atoms.
Thus, the atomic number of the element is 8 and it is oxygen.

oxygen

Which element has the electronic structure 2, 6?

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