Elements, Compounds and Mixtures. Chapter 16

Classification of Substances Elements Molecules Compounds Mixtures.

Elements Elements are substances made up of only one type of atom. Example  Hydrogen, Gold.

Periodic Table of Elements

Molecule A molecule is made up of two or more atoms chemically combined.

Compounds Compounds are made up of two or more different types of atoms chemically combined.

Properties of Compounds When a compound is formed during a chemical reaction its properties differ from those of the elements from which it is made. Example: Water is made from hydrogen and oxygen. Hydrogen  flammable gas Oxygen  colourless gas.

Diagram of Salt, water, sucrose.

Mixtures A mixture consists of two or more different substances mingled together but not chemically combined. Examples:Sea – water and salt Air – nitrogen, oxygen … Soil – sand, clay, humus …

Compare mixtures and Compounds.

MixtureCompound The amounts of the substances in the mixture can vary. The elements in a compound are always present in the same fixed proportion. A mixture contains two or more substances A compound is a single substance. The properties of a mixture are similar to those of the substances in a mixture. The properties of a compound are different to those of the elements which reacted to form it. There are practically no energy changes when a mixture is made Heat is usually given out or taken in when a compound is formed. It is usually easy to separate the components of a mixture. It is usually difficult to separate the components of a compound.

iron particles Key: strong bonds between iron particles one iron particle iron particles held together by strong bonds

iron particles iron particles are attracted to a magnet iron particles diagram

sulfur particles Key: strong bonds between sulfur particles one sulfur particle sulfur particles held together by strong bonds

sulfur particles sulfur particles are not attracted to a magnet sulfur particles diagram

iron particles sulfur particles

A mixture of iron and sulfur particles strong bonds between sulfur particles strong bonds between iron particles What’s this?

A mixture of iron and sulfur particles A magnet attracts the iron particles but not the sulfur particles. The mixture is separated mixture diagram

one sulfur particle one iron particle strong bonds between iron and sulfur particles What’s this? A compound between iron and sulfur particles

strong bonds between iron and sulfur particles A compound between iron and sulfur particles The magnet cannot separate iron and sulfur particles in a compound compound diagram

References Steve Lewis for the Royal Society of Chemistry Photographs by Peter Hollamby

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