Bonding and Structure

• The three main types of chemical bonds are Ionic, Covalent, and Metallic.
• Ionic bonding is the electrostatic attraction between positive and negative ions.
• An example of an ionically bonded substance is NaCl (Sodium Chloride - salt).
• A small amount of energy is enough to overcome the intermolecular forces.
• Simple molecular structures are non conductors.
• Atoms within the same molecule are held by strong covalent bonds and different molecules are held by weak intermolecular forces.
• Simple molecular structures have low melting and boiling point due to the weak intermolecular forces.
• Ionic lattices dissolve in polar solvents such as water.
• Large ionic lattices have high or low melting and boiling point because a large amount of energy is required to overcome the electrostatic bonds.
• When ions are in liquid state, they are mobile and can freely carry the charge.
• Water has a polar bond where Hydrogen atoms have a + charge and oxygen atoms have a - charge.
• Covalent bonding is the electrostatic attraction between a shared pair of electrons and the nuclei.
• Metallic bonding is the electrostatic attraction between the positive metal ions and the sea of delocalised electrons.
• Electrons in the outer shell are represented in a dot and cross diagram.
• Giant ionic lattices conduct electricity when liquid but not when solid because in the solid state the ions are in fixed positions and cannot move.
• A polar bond is formed when bonding atoms have different electronegativities.
• Hydrogen bonding and Van der Waals’ forces are the two types of intermolecular forces.
• Some molecules with polar bonds have permanent dipoles, leading to forces of attraction between those dipoles and those of neighbouring molecules.
• Permanent dipole-induced dipole interactions occur when a molecule with a permanent dipole is close to other non-polar molecules, causing the non-polar molecule to become slightly polar, leading to attraction.
• Hydrogen bonding is the strongest type of intermolecular force.
• Permanent dipole-induced dipole interaction and permanent dipole-permanent dipole interaction are the two interactions that can be referred as Van der Waals’ forces.
• London forces are caused by random movements of electrons, leading to instantaneous dipoles, which induce a dipole in nearby molecules, attracting one another.
• Fluorine is the most electronegative element.
• Triple bond is formed when atoms share three pairs of electrons.
• There are two types of covalent structure: Simple molecular lattice and Giant covalent lattice.
• Dative covalent bond is a bond where both of the shared electrons are supplied by one atom.
• Oxygen forms 2 covalent bonds.
• Charged ions are attracted to atoms that are bonded by a single pair of shared electrons, which is known as a single bond.
• Carbon forms 4 covalent bonds.
• A lone pair is a group of electrons in the outer shell that are not involved in the bonding.
• In simple molecular structures, the bonding is described as a simple molecular lattice.
• Double bond is formed when atoms share two pairs of electrons.
• In giant covalent structures, the bonding is described as a giant covalent lattice.
• Average bond enthalpy is a measure of the average energy needed to break the bond.
• London forces are greater in larger molecules due to more electrons.
• In water, the lattice is collapsed and the molecules are closer together.
• Because O, N and F are highly electronegative, H nucleus is left exposed.
• Ice is less dense than liquid water because in ice, the water molecules are arranged in a orderly pattern and it has an open lattice with hydrogen bonds.
• Water has a melting/ boiling point higher than expected because hydrogen bonds are stronger than other intermolecular forces so extra strength is required to overcome the forces.
• To draw a diagram of hydrogen bonding, draw a line from the H nucleus to the lone pair of electrons on O, N, F.