Bonding

• There are three types of strong chemical bonds: ionic, covalent and metallic.
• For ionic bonding the particles are oppositely charged ions.
• For covalent bonding the particles are atoms which share pairs of electrons.
• For metallic bonding the particles are atoms which share delocalised electrons.
• Ionic bonding occurs in compounds formed from metals combined with non-metals.
• Covalent bonding occurs in most non-metallic elements and in compounds of non-metals.
• Metallic bonding occurs in metallic elements and alloys.
• Ionic bonding involves the transfer of electrons from a metal to a non-metal.
• Covalent bonding involves two non-metals sharing pairs of electrons.
• Metallic bonding occurs between two metals.
• Metals are positive metal ions in a sea of delocalised electrons.
• When a metal atom reacts with a non-metal atom electrons in the outer shell of the metal atom are transferred.
• Metal atoms lose electrons to become positively charged ions.
• Non-metal atoms gain electrons to become negatively charged ions.
• The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0).
• The charge on the ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 relates to the group number of the element in the periodic table.
• An ionic compound is a giant structure of ions.
• Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this is called ionic bonding.
• When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong.
• Covalently bonded substances may consist of small molecules.
• Some covalently bonded substances have very large molecules, such as polymers.
• Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide.
• Metals consist of giant structures of atoms arranged in a regular pattern.
• The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure. The sharing of delocalised electrons gives rise to strong metallic bonds.
• The three states of matter are solid, liquid and gas. Melting and freezing take place at the melting point, boiling and condensing take place at the boiling point.
• The three states of matter can be represented by a simple model. In this model, particles are represented by small solid spheres.
• Particle theory can help to explain melting, boiling, freezing and condensing.
• The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance.
• The nature of the particles involved depends on the type of bonding and the structure of the substance.
• The stronger the forces between the particles the higher the melting point and boiling point of the substance.
• Limitations of the simple model above include that in the model there are no forces, that all particles are represented as spheres and that the spheres are solid.
• In chemical equations, the three states of matter are shown as (s), (l) and (g), with (aq) for aqueous solutions.
• Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions.
• Ionic compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds.
• When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow.
• Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points.
• Small molecules have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.
• The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points.
• Small molecules do not conduct electricity because the molecules do not have an overall electric charge.
• The intermolecular forces are weak compared with the covalent bonds in small molecules