Atoms and molecules
3 marks · NormalExplain why oxygen can exist as O₂ molecules, but helium does not form molecules under normal conditions. Use your knowledge of atoms and molecules.
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Oxygen atoms can join together by forming chemical bonds to make O₂ molecules. Helium atoms do not readily bond with other helium atoms, so they exist as single atoms.
Must show: Oxygen forms bonds – O₂ molecules, Helium does not bond – exists as single atoms
Common mistakes: Saying all elements form molecules; Not mentioning chemical bonding
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Marking points
M1 · 1 mark · States oxygen atoms can bond/form molecules.
B1 · 1 mark · Correctly explains O₂ is a molecule of oxygen atoms joined together.
B1 · 1 mark · Explains helium atoms do not form bonds/molecules.
Worked solution
Oxygen atoms can form covalent bonds with other oxygen atoms, creating O₂ molecules. Helium does not tend to bond with other atoms and so exists as single atoms instead of molecules.