Atoms and molecules
4 marks · NormalUse the table to answer the questions about atoms and molecules.
| Substance | Formula | Atoms present |
|---|---|---|
| Hydrogen | H2 | H |
| Carbon dioxide | CO2 | C and O |
| Argon | Ar | Ar |
Which substance in the table consists of single atoms, not molecules? Explain your answer.
State the number of different types of atoms in a carbon dioxide molecule. Give your reasoning.
For hydrogen, state how many atoms are bonded together in each molecule.
Explain what is meant by a molecule, using an example from the table.
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(a) Argon; because it is a noble gas and exists as single atoms (Ar), not bonded.
(b) 2; carbon and oxygen are present in CO2, so two different types.
(c) 2; each hydrogen molecule (H2) is made of 2 hydrogen atoms bonded together.
(d) A molecule is made when two or more atoms are chemically bonded. For example, H2 is a molecule with two hydrogen atoms bonded.
Common mistakes: Confusing element and molecule; Not recognising Ar as atomic; Counting atoms rather than types
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Marking points
B1 (a) · 1 mark · Identifies argon as atomic and gives valid explanation (exists as single atoms, not molecules).
B1 (b) · 1 mark · Correctly states two types of atoms in CO2 and explains (carbon and oxygen).
B1 (c) · 1 mark · States 2 atoms bonded in each H2 molecule.
B1 (d) · 1 mark · Defines molecule and uses an example from the table.
Worked solution
a) Argon; its formula is Ar, meaning it exists as single atoms not molecules.
b) 2 types of atoms (carbon and oxygen) in carbon dioxide molecule (CO2).
c) Each hydrogen molecule (H2) has 2 hydrogen atoms bonded together.
d) A molecule is formed when atoms are chemically bonded together. Example: H2, with two hydrogen atoms bonded.