Atomic Structure

Learn and apply Atomic Structure in the published Chemistry course sequence.

GCE A-Level H1 Chemistry 8873-2027

Learning goals

identify and describe protons, neutrons and electrons in terms of their relative charges and relative masses
deduce the behaviour of beams of protons, neutrons and electrons in an electric field
describe the distribution of mass and charges within an atom
deduce the numbers of protons, neutrons and electrons present in both atoms and ions given proton and nucleon numbers (and charge)
— describe the contribution of protons and neutrons to atomic nuclei in terms of proton number and nucleon number
— distinguish between isotopes on the basis of different numbers of neutrons present
describe the number and relative energies of the s, p and d orbitals for the principal quantum numbers 1, 2 and 3 and also the 4s and 4p orbitals
describe the shapes of s and p orbitals [knowledge of wave functions is not required]
state the electronic configuration of atoms and ions given the proton number (and charge)
explain the factors influencing the ionisation energies of elements (see the Data Booklet) (see also Section 4)
deduce the electronic configurations of elements from successive ionisation energy data
interpret successive ionisation energy data of an element in terms of the position of that element within the Periodic Table

H1 Atomic Structure learning outcomes

Atomic structure is the evidence chain behind electron arrangements and ionisation-energy data. Follow the sequence from particles to orbitals, configurations and then energetic evidence.

First learning: work through the five lessons in order. Revision: use the quick reference to find the fact or explanation you need, then open that lesson. H1 8873 requires s and p orbital shapes; d-orbital shapes belong to H2 9476.

What You’ll Learn

Use particle, isotope and ion data to determine atomic composition.
Describe s and p orbitals, write electron configurations and explain ionisation-energy evidence.
Deduce electronic structure and Periodic Table position from successive ionisation energies.

Lessons (Recommended Order)

The order is deliberate: each lesson supplies language or evidence used by the next. When revising, jump directly to the lesson matching the gap in your answer.

Subatomic Particles, Isotopes and Ions
Use particle properties, nuclide notation and charge to determine the composition of atoms, isotopes and ions.
Open lesson
Atomic Orbitals: Energies and Shapes
Separate orbital capacity, relative energy and the H1-required s and p shapes without importing d-orbital shape content.
Open lesson
Orbitals and Electron Configuration
Build exam-safe electron configurations for atoms and ions, then connect arrangements to chemical evidence.
Open lesson
First Ionisation Energy Trends
Explain ionisation-energy trends and anomalies using attraction, shielding, distance and subshell energy.
Open lesson
Successive Ionisation Energies
Read large jumps in successive ionisation-energy data to infer valence electrons and Periodic Table position.
Open lesson

Quick Reference

Idea	Exam-ready reminder
Orbital capacity	one orbital holds two electrons; s has one orbital and p has three
First ionisation energy	energy required to remove one electron from each atom in one mole of gaseous atoms
Successive ionisation	a large jump shows removal has begun from an inner shell

For ionisation-energy questions, name the changing factor, state how it changes the attraction between the nucleus and the electron being removed, and then link that attraction to the energy required.

Practice and Check Your Understanding

Use practice in two passes: first without notes, then revisit only the lesson linked to the misconception you exposed.

Atomic Structure Topic Practice
Course-specific 8873 questions with server-graded feedback across the whole topic.
Start topic practice
Atomic Structure: Check Your Understanding
Check the key ideas, read the targeted feedback, then try a fresh question independently.
Practice onlyCheck understanding

Practise

Work through questions with marking and feedback as you learn.

About 10 minutes

Questions are picked at random each time you start. You'll see the answer after each question. It's for practice only and doesn't count towards mastery.

Recent attempts

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This check needs JavaScript to record answers. The reviewed questions are listed below for study.

Which statement correctly describes how mass and charge are distributed in an atom?

Nearly all the mass and all the positive charge are in a very small nucleus of protons (relative mass 1) and neutrons (relative mass 1); electrons (relative mass 1/1836) occupy the much larger surrounding space.
Mass and positive charge are spread evenly through the atom, with electrons embedded in it.
Electrons provide about half of the mass because there are as many electrons as protons.
The nucleus occupies most of the volume of the atom and contains the electrons.

A proton beam and an electron beam enter the same electric field at the same speed. How do their small deflections compare?

They are deflected in opposite directions, and the electron's deflection is about 1840 times larger.
They are deflected in opposite directions through equal angles, because their charges are equal in size.
The proton's deflection is about 1840 times larger, because it has the larger mass.
They are deflected in the same direction, and the electron's deflection is larger.

Which statement about ²⁴Mg²⁺ and ²⁶Mg (magnesium, proton number 12) is correct?

They are isotopes: ²⁴Mg²⁺ has 12 neutrons and 10 electrons, while ²⁶Mg has 14 neutrons and 12 electrons.
²⁴Mg²⁺ has 14 electrons, because the charge is added to the proton number.
They are different elements, because their nucleon numbers are different.
²⁶Mg has 26 protons, because the nucleon number equals the proton number.

Which statement about the 3p, 4s, 3d and 4p subshells in the conventional filling order is correct?

They fill in the order 3p, 4s, 3d, 4p, and every p orbital is dumbbell-shaped along one axis.
They fill in the order 3p, 3d, 4s, 4p, because all of shell 3 fills before shell 4.
They fill in the order 4s, 3p, 3d, 4p, and p orbitals are spherical.
They fill in the order 3d, 4s, 3p, 4p, because d orbitals are lowest in energy.

What is the ground-state electron configuration of Fe³⁺ (iron, proton number 26)?

[Ar] 3d⁵
[Ar] 3d³ 4s²
[Ar] 3d⁶
[Ar] 3d⁴ 4s¹

Why is the first ionisation energy of oxygen lower than that of nitrogen?

In oxygen one 2p orbital holds a pair of electrons, and repulsion between them makes one easier to remove.
Oxygen has a smaller nuclear charge than nitrogen.
The electron removed from oxygen is in a higher-energy subshell than nitrogen's.
The electron removed from nitrogen is paired, so it is harder to remove.

The first four successive ionisation energies of a Period 3 element are 578, 1817, 2745 and 11577 kJ mol⁻¹. Which conclusion is correct?

The element is in Group 13 and its outer electron configuration is 3s² 3p¹.
The element is in Group 2, because the first value roughly triples at the second ionisation.
The element is in Group 14, because four values are listed.
The element is in Group 13 and its outer electron configuration is 3s³.

Practise after feedback

After a check, practise the skills it showed you need to work on.

About 10 minutes

Questions are picked at random each time you start. You'll see the answer after each question. It's for practice only and doesn't count towards mastery.

Recent attempts

History is stored only in this browser.

No completed attempts are saved yet.

This check needs JavaScript to record answers. The reviewed questions are listed below for study.

Which statement correctly describes how mass and charge are distributed in an atom?

Nearly all the mass and all the positive charge are in a very small nucleus of protons (relative mass 1) and neutrons (relative mass 1); electrons (relative mass 1/1836) occupy the much larger surrounding space.
Mass and positive charge are spread evenly through the atom, with electrons embedded in it.
Electrons provide about half of the mass because there are as many electrons as protons.
The nucleus occupies most of the volume of the atom and contains the electrons.

A proton beam and an electron beam enter the same electric field at the same speed. How do their small deflections compare?

They are deflected in opposite directions, and the electron's deflection is about 1840 times larger.
They are deflected in opposite directions through equal angles, because their charges are equal in size.
The proton's deflection is about 1840 times larger, because it has the larger mass.
They are deflected in the same direction, and the electron's deflection is larger.

Which statement about ²⁴Mg²⁺ and ²⁶Mg (magnesium, proton number 12) is correct?

They are isotopes: ²⁴Mg²⁺ has 12 neutrons and 10 electrons, while ²⁶Mg has 14 neutrons and 12 electrons.
²⁴Mg²⁺ has 14 electrons, because the charge is added to the proton number.
They are different elements, because their nucleon numbers are different.
²⁶Mg has 26 protons, because the nucleon number equals the proton number.

Which statement about the 3p, 4s, 3d and 4p subshells in the conventional filling order is correct?

They fill in the order 3p, 4s, 3d, 4p, and every p orbital is dumbbell-shaped along one axis.
They fill in the order 3p, 3d, 4s, 4p, because all of shell 3 fills before shell 4.
They fill in the order 4s, 3p, 3d, 4p, and p orbitals are spherical.
They fill in the order 3d, 4s, 3p, 4p, because d orbitals are lowest in energy.

What is the ground-state electron configuration of Fe³⁺ (iron, proton number 26)?

[Ar] 3d⁵
[Ar] 3d³ 4s²
[Ar] 3d⁶
[Ar] 3d⁴ 4s¹

Why is the first ionisation energy of oxygen lower than that of nitrogen?

In oxygen one 2p orbital holds a pair of electrons, and repulsion between them makes one easier to remove.
Oxygen has a smaller nuclear charge than nitrogen.
The electron removed from oxygen is in a higher-energy subshell than nitrogen's.
The electron removed from nitrogen is paired, so it is harder to remove.

The first four successive ionisation energies of a Period 3 element are 578, 1817, 2745 and 11577 kJ mol⁻¹. Which conclusion is correct?

The element is in Group 13 and its outer electron configuration is 3s² 3p¹.
The element is in Group 2, because the first value roughly triples at the second ionisation.
The element is in Group 14, because four values are listed.
The element is in Group 13 and its outer electron configuration is 3s³.

Check what I know

Start here to see which parts you already know.

About 8 minutes

Answer 7 short questions. It shows what to work on next and doesn't count towards mastery.

Recent attempts

History is stored only in this browser.

No completed attempts are saved yet.

This check needs JavaScript to record answers. The reviewed questions are listed below for study.

Which description of the neutron gives its relative charge, relative mass and location in the atom correctly?

Relative charge 0; relative mass 1; in the nucleus
Relative charge 0; relative mass 1/1836; outside the nucleus
Relative charge +1; relative mass 1; in the nucleus
Relative charge 0; relative mass 0; in the nucleus

Separate beams of protons, neutrons and electrons, all at the same speed, pass between two oppositely charged parallel plates. Which description of their paths is correct?

Electrons curve strongly towards the positive plate, protons curve slightly towards the negative plate and neutrons go straight on.
Electrons and protons are deflected through equal angles in opposite directions and neutrons go straight on.
Electrons curve towards the negative plate, protons towards the positive plate and neutrons go straight on.
Protons curve strongly towards the negative plate, electrons slightly towards the positive plate and neutrons curve slightly towards the negative plate.

Which statement about the species ³²S²⁻ and ³⁴S (sulfur, proton number 16) is correct?

They are isotopes: ³²S²⁻ has 16 neutrons and 18 electrons, while ³⁴S has 18 neutrons and 16 electrons.
They are not isotopes, because they contain different numbers of electrons.
³²S²⁻ has 14 electrons, because a 2− charge means two electrons are removed.
³⁴S has 34 neutrons, because the nucleon number counts the neutrons.

Which statement about the orbitals with principal quantum number 3 is correct?

There is one 3s, three 3p and five 3d orbitals; the 3s orbital is spherical and each 3p orbital is dumbbell-shaped.
The 3s, 3p and 3d orbitals all have the same energy in a many-electron atom.
There are three orbitals in the third shell, one for each subshell.
The 3s orbital is dumbbell-shaped and the 3p orbitals are spherical.

What is the ground-state electron configuration of a chromium atom (proton number 24)?

[Ar] 3d⁵ 4s¹
[Ar] 3d⁴ 4s²
[Ar] 3d⁶
[Ar] 3d³ 4s² 4p¹

Why is the first ionisation energy of aluminium lower than that of magnesium?

The electron removed from aluminium is in a 3p orbital, which is higher in energy and partly shielded by the 3s electrons.
Aluminium has a smaller nuclear charge than magnesium.
The electron removed from aluminium is paired, so repulsion makes it easier to remove.
The aluminium atom has one more electron shell than magnesium.

The first four successive ionisation energies of an element are 738, 1451, 7733 and 10543 kJ mol⁻¹. Which conclusion is correct?

The element is in Group 2 and its outer electron configuration is ns².
The element is in Group 4, because four ionisation energies are given.
The element is in Group 2 and its outer electron configuration is np².
The element is in Group 3, because the jump occurs at the third ionisation energy.

Check my progress

When you feel ready, answer on your own to show what you can do.

About 10 minutes

Answer 7 questions. You'll see your score, the answers and explanations at the end. Your result can count towards your course progress.

Recent attempts

History is stored only in this browser.

No completed attempts are saved yet.

Check again

After practising what your progress check showed, check those skills again.

About 10 minutes

Answer 7 questions. You'll see your score, the answers and explanations at the end. Your result can count towards your course progress.

Recent attempts

History is stored only in this browser.

No completed attempts are saved yet.

Review

Come back later to see whether your learning has lasted.

About 10 minutes

Answer 7 questions. You'll see your score, the answers and explanations at the end. A scheduled review counts towards your course progress only when it is due.

Recent attempts

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Atomic Structure

H1 Atomic Structure learning outcomes

What You’ll Learn

Lessons (Recommended Order)

Subatomic Particles, Isotopes and Ions

Atomic Orbitals: Energies and Shapes

Orbitals and Electron Configuration

First Ionisation Energy Trends

Successive Ionisation Energies

Quick Reference

Practice and Check Your Understanding