Bonding & Properties of Substances National 5 Chemistry Topic 7 Bonding & Properties of Substances

ammeter or bulb battery or lab pack experiments help to find out if substances contain charged particles and whether these particles can move or not conductivity

substances when molten or in solution metal elements and carbon in the graphite form ions free to move and carry the current contain electrons which are free to move ionic compounds always conduct substances never conduct contain electrons which are fixed in place non-metal elements and non-metal compounds

physical properties ionic metallic covalent 3 main types depends on the type of bonding present in a substance physical properties

covalent bonding eg methane a substance made up of two or more atoms joined together by covalent bonds produces molecules electrons shared in pairs between non - metal atoms covalent bonding

electrical conductivity methane is a non – conductor of electricity not attracted to electrodes in a cell methane is made up of neutral molecules electrical conductivity

melting and boiling point methane is a gas at room temperature so methane has a low melting point and boiling point methane molecules only weakly attracted to each other they need little energy to move around melting and boiling point

solubility in polar solvents methane is insoluble in water so methane and water do not mix + - methane molecules are not attracted by polar water molecules solubility in polar solvents

solubility in non-polar solvents so methane is soluble in benzene methane molecules mix well with non-polar solvents like benzene solubility in non-polar solvents

bigger molecules - 1 liquids solids stearic acid solids sucrose (sugar) hexane ethanol liquids they have stronger forces of attraction between them, so melting and boiling points are higher some covalent molecules are much bigger than methane bigger molecules - 1

diamond silica they have very high melting and boiling points because all of the bonds have to be broken to move the atoms at all some molecules (called macromolecules) are made up of a huge covalent network of atoms bigger molecules - 2

ionic bonding positive metal and negative non-metal ions formed Na Cl eg sodium and chlorine electrons transferred from metal to non-metal atoms Na Cl between metal and non-metal atoms Na Cl + - ionic bonding

ionic compounds – melting & boiling point it is a solid at room temperature hence sodium chloride has high melting ( 801OC )and boiling points ( 1413OC ) sodium chloride is made of oppositely charged ions arranged in a crystal lattice the ions attract each other strongly, so it takes a lot of energy to move them about ionic compounds – melting & boiling point

electrical conductivity an electrolyte positive electrode negative electrode - + sodium chloride solution is an electrical conductor molten sodium chloride is an electrical conductor ions are free to move ionic lattice can be broken up by melting or dissolving electrical conductivity

+ - the polar water molecules are strong enough to pull the ions out of the lattice + - the ionic lattice can be broken up by polar molecules like water + - solubility 1

solubility 2 sodium chloride is soluble in water + the ions become surrounded by water molecules - sodium chloride is soluble in water the compound dissolves solubility 2

metallic bonding they hold the atoms together the outer electrons are contributed to a shared ‘pool’ of electrons delocalised electrons metal atoms pack closely together neither covalent nor ionic bonding will give metal atoms a full outer shell between metal atoms metallic bonding

delocalised electrons moving randomly and holding the atoms together metallic bonding

electrical conductivity metals are good conductors of electricity - + they move towards the positive terminal when a supply of electricity is connected the delocalised electrons are not fixed in place electrical conductivity

melting point metals have a lower melting point than ionic solids metal ions in the lattice are not firmly fixed in place they can be moved around without much difficulty melting point

boiling point metals tend to have a high boiling point they are held there by the delocalised electrons it is difficult to remove the metal ions from the lattice boiling point

ductility and malleability because metal ions in the lattice are not firmly fixed in place metals are ductile easily drawn out into wires ductility and malleability easily beaten out into shape metals are malleable

solubility chemical properties the reactions of metals with water (and other substances like oxygen and acids) many of them react with water metals do not dissolve in water solubility

more about ions - colour chromate ions, CrO42-(aq) are yellow permanganate ions, MnO4- (aq) are purple copper(II) ions, Cu2+(aq) are blue nickel(II) ions, Ni2+(aq) are green some ions in aqueous solution have particular colours more about ions - colour many ions in aqueous solution are colourless sodium Na+(aq) potassium K+(aq) sulphate SO42- (aq) chloride Cl- (aq)

more about ions – colour of compounds green colourless copper(II) chromate solution blue sodium chloride solution copper(II) sulphate solution can be predicted from ion colours more about ions – colour of compounds

more about ions - migration copper chromate gel (green) positive ions will migrate (move) towards the negative electrode more about ions - migration negative ions will migrate (move) towards the positive electrode contains Cu2+(aq) & CrO42-(aq) ions

more about ions – migration results a blue colour appears around the negative electrode a yellow colour appears around the negative electrode CrO42- (aq) ions are negatively charged Cu2+ (aq) ions are positively charged copper chromate gel (green)

more about ions chemical changes when an electric current passes through an electrolyte, it brings about process called electrolyte electrolysis a solution contain ions which conducts electricity more about ions

copper(II) chloride solution copper metal – Cu(s) Cu2+ + 2 e- Cu pick up 2 electrons negative electrode Cu2+(aq) copper(II) chloride solution Cl-(aq) positive electrode give away 2 electrons 2 Cl- Cl2 + 2 e- chlorine gas – Cl2(g)