A compound is a substance consisting of two or more elements together. A compound is a substance consisting of two or more elements chemically combined together. What is a Compound?
Some Examples of Compounds Sodium + Chlorine Hydrogen + Oxygen Copper + Sulfur + Oxygen Carbon + Oxygen WaterCopper(II) Sulphate sodium chloride Carbon Dioxide Their constituent elements
Video clip on heating iron and sulphur
1.A compound has properties that are different from the properties of its constituent elements.
Video clip on heating magnesium in air
Video clip on burning sodium in chlorine
2.When a compound is formed, there is usually an exchange of energy (in the form of heat energy or light energy or both) with the surroundings.
3.A compound can only be broken down into simpler substances by chemical methods, such as decomposition by heat energy, exposure to light or passing an electric current through it.)
4.The different elements in a compound always join together in a fixed proportion by mass. For example, 1 g of hydrogen combines with only 8 g of oxygen to form 9 g of water.
Explain why water is a compound? Test Yourself
What is a Mixture? A mixture consists of two or more substances not chemically combined together. What is a Mixture? A mixture consists of two or more substances not chemically combined together. Video clip on mixtures
Some Examples of Mixtures air soil blood sea water aerated water
Video clip on mixing iron and sulphur
1.A mixture has the properties of its components.
2.When a mixture is produced, little or no energy in the form of heat energy or light energy is given out or taken in.
3.A mixture can be separated into its components by physical means such as using a magnet, evaporation, filtration and distillation.
4.The components in a mixture can be mixed in any proportion by mass.
Explain why air is a mixture? Test Yourself
Difference between Elements, Compounds and Mixtures ElementsCompoundsMixtures Made up of only one kind of atom Different elements in a compound combine in a fixed proportion by mass. The components in a mixture are not mixed in any fixed proportion.
ElementsCompoundsMixtures An element is the simplest pure substances A chemical change takes place when a compound is formed. No chemical reaction occurs. There is little or no light or heat taken in or given out. Elements have properties similar to those of their atoms. A compound has properties which are different from the properties of its constituent elements. A mixture has the properties of the substances of which it is made.
ElementsCompoundsMixtures Elements cannot be broken down. A compound can only be broken down, by chemical methods, for example. Heating (decomposition) or by passing electricity through it. A mixture can be separated easily by physical methods, for example, filtration, distillation, evaporation.
Word Equations are commonly used for representing chemical reactions. e.g. 1. iron + sulfur iron sulfide 2. magnesium + oxygen magnesium oxide
Word Equations are commonly used for representing chemical reactions. 4. iron + hydrochloric acid hydrogen + iron chloride 3. oxygen + hydrogen water
Video clip on reaction between (a) iron and sulphur and (b) calcium and water