Atoms

An atom of gallium has an atomic number of 31 and a mass number of 70. Give the number of electrons, protons and neutrons in the atom.

• 31 electrons, 31 protons, 39 neutrons

• 31 electrons, 31 protons, 40 neutrons

• 31 electrons, 32 protons, 39 neutrons

• 32 electrons, 31 protons, 39 neutrons

What is an element?

• A substance that cannot be broken down into simpler substances

• A mixture of two or more substances

• A compound made of different atoms

• A type of molecule

Atoms can have different numbers of protons, neutrons, and electrons. What determines the type of atom?

• The number of protons

• The number of neutrons

• The number of electrons

• The number of protons and neutrons

An atom with one proton in its nucleus is:

• hydrogen

• helium

• lithium

• beryllium

Which of the following is a correct symbol for an element?

• C for carbon

• O for oxygen

• Mg for magnesium

• All of the above

A substance consists of atoms which all have the same number of protons and electrons but different numbers of neutrons. Explain why this substance is an element.

• Because it has a unique atomic number.

• Because it has isotopes.

• Because it is a compound.

• Because it has a unique atomic mass.

Calculate silicon's relative atomic mass to 1 decimal place.

• 28.1

• 28.0

• 28.2

• 28.3

When elements react, atoms combine with other atoms to form _______.

• molecules

• compounds

• mixtures

• solutions

Compounds are substances formed from two or more elements, the atoms of each are in fixed proportions throughout the compound and they're held together by _______.

• chemical bonds

• physical forces

• magnetic attraction

• gravitational pull

Making bonds involves atoms giving away, taking or sharing _______. Only the _______ are involved—the nuclei of the atoms aren't affected at all when a bond is made.