Elements & Compounds (GCSE Chemistry)
Elements & Compounds
Atoms
All substances are made out of atoms. An atom is the smallest unit of all matter. An atom is the smallest part of an element that can exist.
A molecule is made of a fixed number of atoms, which are covalently bonded together.
Elements
Periodic Table
- An element is made of one type of atom. Elements are made up of atoms, and each element only has one type of atom. For example, oxygen is only made up of oxygen atoms.
- Elements are arranged in the periodic table. There are about 100 different elements, which are arranged in the periodic table based on their properties.
- Elements are arranged by atomic number. All elements are arranged in the periodic table in ascending order of atomic number. Elements are represented using a symbol which is usually one or two letters for e.g. C = Carbon and Na = Sodium.
Compounds
- What is a compound? A compound is a substance that contains two or more elements chemically combined together. The elements in each compound are present in fixed proportions – for example in carbon dioxide (CO2) for every gram of carbon there is 2g of oxygen.
- The formation of compounds involves breaking and making bonds. Making a compound involves making bonds between atoms. Sometimes you also need to break bonds in the reactants. usually results in a change in energy which can be detected. So either energy is required for the formation or energy is made during the formation.
- Making and breaking bonds involves electrons. Electrons can either be shared, lost or gained to form chemical bonds. For example, covalent bonds are formed when electrons are shared, and ionic bonds are formed when electrons are transferred from metal to non-metal.
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