Compounds, Elements & Mixtures 1st Year Chemistry

Elements Elements & Atoms All substances are made up from tiny particles called atoms. When a substance is made up of only one type of atom it is called an element. The element iron is made up of iron atoms, the element hydrogen is made up of hydrogen atoms, the element sulphur is made up of sulphur atoms and so on.

Definitions An atom is the smallest particle of an element that still retains the properties of that element. An element is a substance that cannot be broken down into simpler substances by chemical reactions.

Compounds Compounds and elements When elements combine together by means of a chemical reaction, they form new substances called compounds. When the elements hydrogen and oxygen combine together, they form the compound water H²0.

Water The compound water is a colourless liquid. The elements used to make water have different physical and chemical properties. Hydrogen and oxygen are colourless gases and are highly reactive. A compound is formed when two or more elements combine chemically.

Elements Compounds Hydrogen (H2) colourless, odourless, tasteless gas: explosive when mixed with oxygen. Oxygen (O²) Colourless, odourless, tasteless gas: Substances need oxygen to burn Water (H²O) Colourless liquid, nice taste, essential for life, It does not burn. Excellent solvent. Carbon (C) Black Solid Carbon Dioxide (CO²) Colourless, odourless, tasteless gas: does not allow substances to burn Magnesium (Mg) Silver metal solid Oxygen (O²) Colourless, odourless gas: Fuels need oxygen to burn Magnesium oxide (MgO) solid, white powder Iron (Fe) dark grey metal. It is attracted to magnets Sulphur (S) Yellow solid Iron Sulphide (FeS) black solid. It is not attracted to magnets

Molecules & Compounds A molecule is two or more atoms chemically combined together. It is the smallest particle of an element or a compound that can exist on its own. Hydrogen (H²) and oxygen (O²) are molecules. They are made from molecules of elements. Carbon dioxide (CO²) and methane (CH4) are compounds. They are made from molecules of compounds. Sodium Chloride (NaCl) and magnesium oxide (MgO) are compounds. The elements are joined together in giant structures called lattices and are not molecules.

Compounds & Mixtures All substances are not made up of elements combined together chemically. Many are just mixed or jumbled up together. Substances like air, seawater and crude oil are mixtures. Mixtures of metals are called alloys A mixture is formed when two or more substances are put together, but are not chemically combined. When sulphur and iron filings are mixed together they form a mixture When sulphur and iron filings are heated together, they form a compound called iron Sulphide (FeS)

Physical & Chemical Changes Physical Changes Ice changing into water, water changing into steam and magnetising a piece of iron are some examples of physical changes. In each case new properties may be gained, but there is no change in mass. A physical change is a change in which no new substance is formed, but the original substance gains new properties Chemical Changes Burning fuels, burning magnesium and rusting iron are examples of chemical changes. A chemical change is a change in which at least one new substance is formed.

Physical & Chemical Changes Physical Changes Chemical Changes No new substance formed One or more new substances formed No change in mass Usually a change in mass Can be easily reversed Not easily reversed No heat involved Heat usually involved

Compounds & Mixtures The mixture can be separated using a magnet. After being heating the mixture becomes a compound and cannot be separated using a magnet.

Differences Between Compound & Mixtures Compounds, Elements & Mixtures Differences Between Compound & Mixtures Mixtures Compounds Consists of two or more substances Consists of one substance The amount of the substances can vary The amount of the elements are fixed Can often be easily separated Can only be separated into its elements by a chemical reaction Properties are similar to the substances used to make the mixture Properties are different to the substances used to make the compound

Questions What is an element? List three elements and their chemical symbols. Compounds are made up of 2 or more ________ which are chemically ___________. A mixture is made up of 2 or more __________ which are mingled together but not _______ __________.

The smallest part of an element is called an ________ The smallest part of an element is called an ________. All the __________ in an element are the same. Therefore elements cannot be ________ _________ into simpler substances.