Atoms and molecules
3 marks · EasyAnswer the following about atoms and molecules.
Define a molecule.
Give an example of a molecule formed from atoms of two different elements.
Explain why atoms of helium (He) are not classed as molecules.
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(a) A molecule is two or more atoms chemically bonded together.
(b) Example: water, H₂O (or carbon dioxide, CO₂, or any suitable correct example).
(c) Helium atoms do not bond with each other; they exist as single atoms.
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Marking points
B1 (a) · 1 mark · Correctly defines a molecule as two or more atoms chemically bonded.
B1 (b) · 1 mark · Any correct example of a molecule composed of two or more different elements (e.g., H₂O, CO₂).
B1 (c) · 1 mark · Correct explanation: Helium atoms do not bond to form molecules; they exist as single atoms.
Worked solution
a) A molecule is made up of two or more atoms chemically bonded together. b) Water (H₂O) is a molecule made of hydrogen and oxygen atoms. c) Helium atoms do not join with other atoms; each helium exists as a single atom, not a molecule.