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It was once thought that electrons orbited the nucleus of an atom like planets around a star.

Chemistry - Atoms (AQA)

Explore the structure of atoms, from protons and neutrons in the nucleus to electrons in shells. This GCSE Chemistry quiz supports AQA Atomic Structure topics.

Explore the Topic →

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Fascinating Fact:

Protons have charge +1 and mass 1, neutrons have charge 0 and mass 1, electrons have charge −1 and a very small mass.

In GCSE Science (Chemistry), you study how atoms are built from subatomic particles. Understanding charge, mass, atomic number and mass number helps explain elements, isotopes and chemical reactions.

Key Terms

Atom: The smallest particle of an element that can take part in a chemical reaction.
Nucleus: The tiny, dense centre of an atom that contains protons and neutrons.
Atomic number: The number of protons in an atom, which decides which element it is.

Frequently Asked Questions (Click to see answers)

What are the three main particles in an atom for GCSE Chemistry?

The three main subatomic particles are protons, neutrons and electrons. Protons and neutrons are in the nucleus, while electrons move around it in shells or energy levels.

How do atomic number and mass number differ in GCSE Science?

Atomic number is the number of protons in an atom. Mass number is the total number of protons plus neutrons, so it is usually larger than the atomic number.

Why are electrons important when explaining chemical reactions?

Chemical reactions mainly involve electrons in the outer shells of atoms. Atoms lose, gain or share these electrons to form ions and covalent bonds.

Try These Related Quizzes

1 .

An element is made up from what?

Molecules

Compounds

Two or more different types of atom

One type of atom

An easy start - or was it? If you don't know your definitions of elements and compounds, revise them hard before the exam arrives

2 .

Which of the following elements is not found in CaHCO₃?

Calcium

Carbon

Cobalt

Oxygen

Atoms are represented by symbols. Where the symbol has more than one letter, only the first one is a capital. That's what makes this question tricky. A lot of students see the CO part of the formula and immediately think it is cobalt. It is not as there are 2 capital letters. So the moral of this is to pay attention to the capital letters!

3 .

What particles are present in the nucleus of an atom?

Protons only

Neutrons only

Electrons only

Protons and neutrons

Ernest Rutherford was the famous scientist who lead the team that discovered the nucleus

4 .

Where are the electrons found?

In a single group close to the nucleus

Orbiting the nucleus like the planets of the Solar System

In 'shells' surrounding the nucleus

Fixed in place at different distances from the nucleus

The shells are not physical things, they are just the areas where you will find the electrons as they orbit the nucleus. They can also be referred to as energy levels

5 .

Which of the following give the charges in order for the proton, neutron and electron?

+1, 0, -1

0, +1, -1

-1, +1, +1

+1, +1, -1

If you weren't sure, you can remember the charges like this:
Protons - P for positive
Neutrons - NEUT for neutral
So the electrons must be negative

6 .

Which of the following statements is true in an atom?

The number of protons is always equal to the number of electrons

The number of protons is always equal to the number of neutrons

The number of protons is sometimes equal to the number of electrons

The number of protons is never equal to the number of electrons

The important thing to remember about atoms is that they are electrically neutral so the positive charges of the protons are balanced by having the same number of electrons. If they are not the same, you have an ion, not an atom

7 .

Atoms of a particular element all have the same number of what?

Particles

Nuclei

Neutrons

Protons

The number of protons is what gives each element its own unique identity. So all atoms that contain 6 protons in the nucleus will be the element carbon, regardless of the number of neutrons

8 .

The element Argon has an atomic number of 18 and a mass number of 40. Which of the following statements is true.

Argon has 18 protons and 22 neutrons

Argon has 18 neutrons and therefore 18 electrons

Argon has 18 electrons and 22 protons

Argon has 18 neutrons and 22 protons

The atomic number gives you the number of protons (and therefore the number of electrons) in the atom. It is sometimes called the proton number.The mass number is the total number protons plus neutrons. If you subtract the atomic number from the mass number you get the number of neutrons

9 .

Which of the following represents the arrangement of the 18 electrons in the Argon atom?

2.8.6.2

2.8.2.6

8.10

2.8.8

The first 3 electron shells (energy levels) are all complete which is what makes it so difficult to get argon to react with anything

10 .

The element sodium has an atomic number 11 and mass number 23. Which of the following gives the correct number of protons, neutrons and the electron arrangement in the correct order?

23, 11, (2.8.1)

12, 11, (2.6.3)

11, 12, (2.8.1)

11,12, (8.2.1)

Sodium is in group I of the periodic table because it has 1 electron in its outer energy level

You can find more about this topic by visiting BBC Bitesize - Atoms, elements and compounds - AQA

Author: Kev Woodward (PGCE, Science & Chemistry Teacher, Quiz Writer)