Summary Chemistry Unit 1 Booklet

A-Level Chemistry
Topic 1
Atomic Structure and the
Periodic Table




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,Topic 1: Atomic Structure and The Periodic Table - Specification




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, KEY DEFINITIONS
1. An atom is the smallest particle of matter than can exist on its own.

2. An element is a substance which contains only one type of atom.
(E.g. oxygen, magnesium, sodium)

3. A molecule is formed when 2 or more atoms join together. The atoms can be the same or different. We
usually reserve the term molecule for simple covalent structures.
(E.g. H2, NH3)

NB. If the atoms joining together are the same, e.g. two hydrogen atoms coming
together to form the H2 molecule, the molecule is STILL an element.

4. A compound is two or more different atoms chemically joined together. Compounds can be ionic or
covalent, as long as they have 2 or more different atoms

EXAMPLES:
E.g. 1: hydrogen bromide is a compound made up of molecules.
E.g. 2. Two hydrogen atoms join to one oxygen atom to form a new compound called water.


5. A mixture is composed of two or more separate
substances.




Questions on Definitions:

(Circle the correct answers. More than 1 may be correct for each one)

Is water, H2O, an element, a molecule, a compound, a mixture

Is oxygen, O2, an element, a molecule, a compound, a mixture

Is sodium chloride, NaCl an element, a molecule, a compound, a mixture




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