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The first energy level holds up to 2 electrons and the second and third up to 8, so sodium is 2,8,1. Free notes with key terms and 11 questions answered.
Electronic Structure and Energy Levels is part of A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes in GCSE AQA Higher Chemistry.
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The first energy level holds up to 2 electrons and the second and third up to 8, so sodium is 2,8,1. Free notes with key terms and 11 questions answered.
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Use this lesson to stay inside A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes while connecting the detail back to the wider Topic 1: Atomic structure and the periodic table topic.
Read the core explanations from Electronic Structure and Energy Levels before testing yourself from memory.
Why do sodium and chlorine react so violently, but helium won't react with anything? The answer lies in how their electrons are arranged.
Electronic structure determines everything about an atom's behaviour - whether it conducts electricity, what compounds it forms, even its position in the periodic table. Understanding electron arrangement is your key to predicting chemical reactions.
Think of energy levels like floors in a hotel. Electrons always check into the lowest available floor first - they're energy-efficient. The first energy level (ground floor) holds a maximum of 2 electrons. The second level holds up to 8 electrons. The third level can hold up to 18, but for GCSE we only consider the first 8 positions.
Electronic structure can be written in two ways: as numbers separated by commas, or as a diagram. Both show the same information - how electrons are distributed across energy levels.
Worked example: Finding Electronic Structure of Sodium (11 electrons)
Sodium has 11 electrons. Write its electronic structure.
Answer: 2,8,1
The same information can be shown in a diagram with circles representing energy levels and dots or crosses representing electrons. Sodium's diagram would show 2 electrons in the inner circle, 8 in the middle circle, and 1 in the outer circle.
Electrons follow strict rules when filling energy levels. These rules explain why atoms behave the way they do and help you predict electronic structures.
This filling pattern explains chemical behaviour. Atoms with full outer energy levels (like noble gases) are unreactive. Atoms with 1 electron in their outer level (like sodium) readily lose that electron. Atoms with 7 electrons in their outer level (like chlorine) readily gain 1 electron.
Electronic structure questions appear frequently in GCSE exams. Examiners test whether you can work out electron arrangements and link them to chemical behaviour.
Worked example: Exam-Style Question: Electronic Structure
An element has atomic number 17. Draw a diagram to show the arrangement of electrons in its atoms. [3 marks]
Answer: Diagram showing electronic structure 2,8,7 (chlorine)
Common exam mistakes: Students often forget that the atomic number equals the number of electrons in a neutral atom. They also sometimes fill energy levels in the wrong order or exceed the maximum capacity of each level.
Exam precision note: In Electronic Structure and Energy Levels - Electronic structure - A simple model of the atom, symbols, relative atomic mass, electronic charge and isotopes, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
At GCSE, electron arrangement is described using the shell model for the first 20 elements: 2 in the first shell, then up to 8 in the second and third shells. This model is simplified but it is the correct one to use in exam answers about sodium, magnesium, chlorine, and similar first-20 elements.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
The electronic structure of sodium is 2,8,1. Sodium has 11 electrons: 2 fill the first energy level, 8 fill the second, and the remaining 1 goes in the third energy level.
At GCSE, the first energy level (shell) holds a maximum of 2 electrons, and the second and third shells hold up to 8 electrons each, for the first 20 elements. Electrons always fill the lowest available energy level first.
Energy levels are fixed regions around the nucleus where electrons can exist, also called electron shells. They are numbered 1, 2, 3 from innermost to outermost, and electrons occupy the lowest available level first.
Electronic structure is shown in a diagram with circles representing energy levels and dots or crosses representing electrons. Sodium's diagram has 2 electrons in the inner circle, 8 in the middle circle and 1 in the outer circle.
To work out electronic structure, use the atomic number to find the number of electrons, then fill energy levels from the innermost: up to 2 in the first, then up to 8 in the second and third. Sodium, with 11 electrons, is 2,8,1; chlorine, with 17, is 2,8,7.
Atoms with full outer energy levels, like the noble gases, are unreactive. Atoms with 1 electron in their outer level, like sodium, readily lose that electron, and atoms with 7 electrons in their outer level, like chlorine, readily gain 1 electron.
To draw an electron diagram, draw concentric circles for the energy levels and show the electrons as dots or crosses. For an element with atomic number 17, draw 3 circles with 2 electrons in the inner circle, 8 in the middle and 7 in the outer circle, giving 2,8,7.
The first energy level, the innermost shell, fills first and holds a maximum of 2 electrons. Electrons always occupy the lowest available energy level, then the second level, which holds up to 8.
Noble gases are unreactive because they have full outer energy levels. Atoms with 1 outer electron, like sodium, readily lose it, and atoms with 7, like chlorine, readily gain 1 electron.
For the first 20 elements, the third shell holds up to 8 electrons at this level, although it can hold up to 18. The shell model uses 2 in the first shell, then up to 8 in the second and third shells.
An element with atomic number 17 has 17 electrons, arranged as 2,8,7: 2 in the first level, 8 in the second and 7 in the third. This is chlorine.