1.2. Elements and Chemical Compounds. Pure Substances and Mixtures

Last Updated: 18 August 2019 | Print

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Elements and chemical compounds

An element consists of only type of atom.

Examples:

Iron, Fe
Sulfur, S

Iron filings consist only of iron atoms, Fe.

Sulfur powder consists only of sulfur atoms, S

Mix the together and you have – a mixture of iron and sulfur.

Mixture:

Two or more substances/chemical compounds included.
The substances can relatively easy be separated from each other.
The substances maintain their original properties.

Example:

Iron is still magnetic.
Sulfur is still yellow.

In a mixture of iron and sulfur, the sulfur is still yellow …

… and the iron is still magnetic.

Iron sulfide has different properties than iron and sulfur.Chemical compound

Characteristics differ from original elements

If you heat the mixture of iron and sulfur, it reacts, forming iron sulfide, FeS.

Different color, not magnetic.

Pure substances

Contain only one type of substance/chemical compound.

Examples

Iron sulfide, FeS
Water, H₂O
Gold, Au
Sucrose, C₁₂H₂₂O₁₁

Homogenous and heterogenous mixtures

Homogenous mixtures look the same, all the way through.

May be in gaseous, liquid or solid form.

Examples:

Air
Salt dissolved in water
Bronze

Liquid homomgenous mixtures = solutions

Solid homogenous mixtures = alloys

A solution of salt in water is homogenous.

A bouillabaisse is a heterogenous mixture.

The classification of matter

Matter may be classified as mixtures or pure substances. These may be further classified as shown in the picture. Examples of each type is shown at the bottom.

Some separation techniques

When filtrating, a mixture of a solid and a liquid is poured over a filter. The solid stays on the filter while the liquid passes through.

In distillation, you take advantage of the fact that two mixed liquids have different boiling temperatures. The liquid with the lowest boiling temperature evaporates first, and is distilled off.

If two liquids don't mix, they may be separated using a separation funnel. The liquid with the highest density is poured out via the tap at the bottom.

If a solid substance is dissolved in a liquid, e.g. water, the two substances may be separated if the water evaporates.

Mr. Ehinger's Chemistry

1. States of Matter. The Atom and the Periodic Table