chemical bonding

• atoms can chemically bond in 3 ways: ionic bonding, covalent bonding or metallic bonding
• ionic bonding involves an attraction between oppositely charged ions
• ionic bonds are found in compounds made of metals and non-metals
• covalent bonding involves 2 atoms sharing 1 or more pairs of electrons
• covalent bonds are found in most non-metal elements and in non-metal compounds
• metallic bonding involves an attraction between positively charged ions and negatively charged delocalised electrons
• metallic bonds are found in metals and alloys
• ions are particles that have charge and are created when an atom or molecule gains or loses electrons - gaining electrons creates a negatively charged ion, losing electrons creates a positively charged ion
• positive ions are usually creates when an atom of molecule loses electrons
• positive ions are also known as cations
• the metals in group 1 and 2 can easily lose electrons to become positively charged ions
• negative ions are usually created when an atom or molecule gains electons
• negative ions are also called anions
• the no-metals in group 7 are most likely to gain electrons to fill up their electron shell and become negatively charged
• ions can contain multiple elements, an can be made up of either 1 atom, or combinations of atoms with an overall charge
• when atoms form ions, they try to fill up or empty their outer electron shell
• in ionic bonding, a metal atom transfers both electrons to a non-metal atom, allowing both of them to have a full outer electron shell
• group 1 metals lose 1 electron resulting in the formation of positive ions with a charge of +1
• group 2 metals always lose 2 electrons resulting in the formation of doubly positive ions
• non-metal atoms always gain electrons resulting in the formation of negative ions
• noble gases already have a full outer shell so they are unreactive and don't normally form ionic bonds with other elements
• you can work out the proportion of each ion in a compound
• the empirical formula of an ionic compound is the simplest ratio of ions possible
• ionic compounds form giant structures called ionic lattices that are held together by strong electrostatic forces of attraction between positive and negative ions, these forces are called ionic bonds
• covalent bonds are strong because the shared electrons are attracted to the nucleus of both atoms
• covalently bonded substances can be small molecules e.g. water
• covalently bonded substances can be large molecules e.g. polymers
• covalently bonded substances can be giant covalent structures e.g. diamond
• metallic bonding are the electrostatic attractions between positive ions and delocalised negative electrons
• metals are giant structures of regularly arranged atoms, the structure being a regular lattice of positive ions in a 'sea' of delocalised electrons
• delocalised electrons are not bound to an atom and are free to move around within the lattice
• delocalisation happens because metal atoms have a small number of electrons in their outer shells
• there are many ways of representing covalent bonds in a molecule
• dot and cross diagrams: dots represent the outer shell electrons of atoms of 1 element, crosses represent the outer shell electrons of atoms in the other element. a limitation is that it shows electrons differently for each atom, when they are actually exactly the same
• dot and cross diagrams without shells: dots represent the outer shell electrons of atoms in 1 element, crosses represent the outer shell electrons of atoms in the other element
• ball and stick diagrams: balls represent atoms, sticks represent bonds between atoms. a limitation is that atoms are much closer together than the diagram shows
• line diagrams: the atomic symbol represents the atom, lines between the atoms represent a covalent bond
• dot and cross diagrams can show electrons being transferred and ions being formed
• square brackets and a charge represent ions on dot and cross diagrams
• dot and cross diagrams can be used to represent covalent bonds and to show the sharing of electron pairs