What is the atomic number?

The number of protons in an atom.

What is the mass number?

The number of protons plus neutrons in the nucleus.

How do you work out the number of neutrons?

Mass number minus atomic number.

Why is an atom neutral?

It has equal numbers of protons (+1) and electrons (-1), so the charges cancel.

An atom that has gained or lost electrons, so it is charged.

Atoms of the same element with the same number of protons but different numbers of neutrons.

Why is the relative atomic mass of chlorine 35.5?

It is the average of the isotopes chlorine-35 and chlorine-37, taking account of how much of each there is.

Atomic structureIB MYP Sciences: Flashcards

Card 1 of 130 of 13 known

Question

What are the three subatomic particles?

Tap or press Space to reveal

Tap card or press Space to flip

See all 13 cards

What are the three subatomic particles?: Protons, neutrons and electrons.
State the relative charge and mass of a proton.: Charge +1, mass 1.
State the relative charge and mass of a neutron.: Charge 0, mass 1.
State the relative charge and mass of an electron.: Charge -1, mass negligible.
Where are protons and neutrons found?: In the nucleus.
Where are electrons found?: In shells around the nucleus.
What is the atomic number?: The number of protons in an atom.
What is the mass number?: The number of protons plus neutrons in the nucleus.
How do you work out the number of neutrons?: Mass number minus atomic number.
Why is an atom neutral?: It has equal numbers of protons (+1) and electrons (-1), so the charges cancel.
What is an ion?: An atom that has gained or lost electrons, so it is charged.
What are isotopes?: Atoms of the same element with the same number of protons but different numbers of neutrons.
Why is the relative atomic mass of chlorine 35.5?: It is the average of the isotopes chlorine-35 and chlorine-37, taking account of how much of each there is.

Exam questions on Atomic structure

An aluminium atom has atomic number 13 and mass number 27. Aluminium is recycled in large quantities because it can be melted and reused many times.
Explain why an aluminium atom has no overall electrical charge.2 marks
Table salt contains sodium ions. A sodium atom has atomic number 11 and mass number 23. When sodium reacts, each atom forms a sodium ion with a charge of +1.
Explain how a sodium atom becomes a sodium ion with a charge of +1.2 marks
Carbon exists as several isotopes. The three most common are carbon-12, carbon-13 and carbon-14. All three have atomic number 6.
Describe how atoms of these three isotopes are similar and how they are different, in terms of protons, neutrons and electrons.3 marks

See the full worksheet

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).