Atomic Structure

Which two lines in the table show particles that are isotopes of the same elements?

• W and Y

• X and Z

• W and Y

• Y and Z

Answer explanation

Isotopes must have the same number of protons but a different number of neutrons

An atom of tin has 74 neutrons.

Which of the following is the mass umber of this atom?

You may wish to use the data booklet to help you.

• 50

• 74

• 118.5

• 124

Answer explanation

The atomic number of tin is 50, so it must have 50 protons. Mass number = protons + neutrons.

An atom is neutral because;

• The number of protons equals the number of neutrons

• The number of electrons equals the number of protons

• The number of electrons equals the number of protons plus neutrons

• The number of neutrons equals the number of electrons plus protons

Answer explanation

Protons and positive and electrons are negative. If there are equal numbers of positive and negative particles, they cancel each other out.

An atom is an atomic number of 15 and a mass number 31. The atom has

• 15 protons and 15 electrons

• 15 protons and 16 electrons

• 16 protons and 15 electrons

• 16 protons and 16 electrons

Answer explanation

Atomic number = protons

Mass number = protons + neutrons

Which of the following particles contains a different number of electrons from the others?

You may wish to use your data booklet.

• Cl⁻

• S²⁻

• Ar

• Na⁺

Answer explanation

Check the number of electrons by using the atomic number and checking the charge.

Positive ions have lost electrons, negative ions have gained electrons.

A sample of tin contains three different isotopes. What is meant by the term isotope?

The three isotopes of tin are shown. The average atomic mass of this sample is 119.4. State the mass number of the most common type of atom in the sample of tin.

Draw a diagram to show the electron arrangement of a magnesium atom.

Explain what would happen if magnesium was to form an ion?

What charge would the magnesium ion have?