2.11Chapter 2: Elements, Compounds and Mixtures

Comparing elements, mixtures, and compounds — Alhussan Chemistry - Stage 7 Revision Notes & Topical Questions

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2.11 Comparing elements, mixtures, and compounds — Alhussan International Academy — Chemistry (Stages 7–9) notes: Classify a substance as an element, a compound or a mixture and justify the choice using properties and particle diagrams.Element — it contains one type of atom and c…

Pure substances
Combinations
Question 1
Question 2
Question 3
Iron sulfide

Section 1 of 8Three types of matter

Three types of matter

Element

Element it contains one type of atom and cannot be split into other substances.
Iron and sulfur are both elements, and sulfur atoms differ from iron atoms.

Compound

Compound it contains two or more elements chemically bonded in a fixed ratio.

Mixture

Mixture it contains two or more substances that are not chemically bonded.
- (elements, compounds or both)

Pure substances

Pure substances elements and compounds are both pure, and mixtures are not.

Section 2 of 8Iron and sulfur

Elements

7 g of iron powder is attracted to a magnet and 4 g of sulfur powder is separate and yellow.

Mixture

Mixture when the two are mixed, both can still be seen and a magnet separates them.
The properties are similar to the properties of the elements.
The elements have not joined, so there can be any amounts of iron and sulfur and they are easy to separate.
Carbon disulfide can also dissolve the sulfur.

Compound

Compound when the mixture is heated the elements join to form iron sulfide, FeS.
The iron cannot be taken out with a magnet.
The properties of the compound differ from the properties of the elements.
Iron sulfide always has 7 g of iron for every 4 g of sulfur.

Section 3 of 8Sodium and chlorine

Elements

Elements sodium is a shiny metal that fizzes in water and may explode, and chlorine is a green, smelly, poisonous gas at 20 °C.

Mixture

Mixture a mixture of the two could kill.

Compound

Compound when they join they make sodium chloride, the table salt added to food.

Section 4 of 8Comparison table

Feature	Element	Mixture	Compound
Single substance	Yes	No	Yes
Types of atom	One	Two or more	Two or more
Composition	Fixed	Variable	Fixed ratio
Properties	Its own	Those of the parts	New, different from the elements
Separation	Cannot be split chemically	By physical methods	By chemical reactions
Substances joined	No	No	Yes, atoms are bonded
Melting point	Sharp	Range	Sharp
Example	Oxygen, iron	Air, sea water	Water, salt

Section 5 of 8Using particle diagrams

Using particle diagrams

Element

Element it shows one kind of circle only, whether single or in pairs.

Compound

Compound it shows different circles joined, with the same arrangement in every unit.

Mixture

Mixture it shows different particles not joined, or different molecules, in no fixed pattern.

Check

Check if every unit is identical the substance is pure, and if the units differ it is a mixture.

Combinations

Combinations separate atoms of two kinds form a mixture of two elements, and joined pairs of unlike atoms alone form a compound.
Joined unlike pairs plus separate atoms of a third kind form a mixture of a compound and an element.

Section 6 of 8Classifying substances

Classifying substances

Question 1

Question 1 is it made of one type of atom?
Then it is an element.

Question 2

Question 2 is it made of different atoms in a fixed ratio with a single formula?
Then it is a compound.

Question 3

Question 3 is it made of more than one substance with no fixed formula that can be separated physically?
Then it is a mixture.

Examples

Examples brass, air, ink and milk are mixtures;
- helium, sulfur and iron are elements;
- ammonia, methane and calcium carbonate are compounds.

Evidence

Evidence support each classification with the formula, particle picture, melting point or whether it can be separated physically.

Section 7 of 8Key terms

Term	Meaning
Element	A substance made of one type of atom.
Compound	A substance with two or more elements chemically bonded in a fixed ratio.
Mixture	Two or more substances not chemically joined.
Pure substance	A substance with only one element or one compound.
Iron sulfide	A compound of iron and sulfur, FeS.
Chemically bonded	Joined by strong forces between atoms.