Edexcel GCSE 9-1 Chemistry: SC5/6/7- Ionic and Covalent Bonding, Types of Substance

Paper 1 and Paper 2 Specification: https://qualifications.pearson.com/content/dam/pdf/GCSE/Science/2016/Specification/GCSE_Chemistry_Spec.pdf

Explain how ionic bonds are formed

by the transfer of electrons between atoms to produce cations and anions, including the use of dot and cross diagrams

Recall that an ion is…

an atom or group of atoms with a positive or negative charge

Explain the formation of ions in ionic compounds from their atoms

• atom gains electrons = - anion (more electrons)

• atom loses electrons = + cation (more protons)

Explain the use of the endings –ide and –ate in the names of compounds

• negatively charged ions formed from single non-metal atoms take the name of the element but end in -ide (fluorine -> fluoride)

• negatively charged ions in compounds containing two or more elements, one of which is oxygen, end in -ate (sulphur + oxygen -> sulphate)

• positively charged ions formed from hydrogen, or metal atoms take the name of the element (hydrogen -> hydrogen ion)

Deduce the formulae of ionic compounds (including oxides, hydroxides, halides, nitrates, carbonates and sulphates) given the formulae of the constituent ions.

oxide = O_{2 ^2-}

hydroxide = OH^-

halides = Fl^- , Br^- , I^-

nitrate = NO_{3 ^1-}

carbonate = CO_{3 ^2-}

sulphate = SO_{4 ^2-}

Explain the structure of an ionic compound as a lattice structure consisting of…

• a lattice structure

• consisting of a regular arrangement of ions

• held together by strong electrostatic forces (ionic bonds) between oppositely-charged ions

Explain the properties of ionic compounds limited to:
(a) high melting points and boiling points, in terms of forces between ions

• high melting points and boiling points

• in a solid state at room temperature

• there are many strong ionic bonds which require large amounts of energy to be transferred to the lattice structure to break

Explain the properties of ionic compounds limited to:
(b) whether or not they conduct electricity as solids, when molten and in aqueous solution

• ions are not free to move around to carry an electric charge

• therefore ionic compounds do not conduct electricity in a solid state

• but when compounds are in an aqueous solution or molten state, ions are free to move and carry an electric charge, therefore conduct electricity

Explain how a covalent bond is formed when a pair of electrons is shared between two atoms

• covalent bonds are usually formed between non-metal atoms and are produced by sharing pairs of electrons

• the atom then becomes more stable as the shared electrons complete their outer electron shell

Recall that covalent bonding results in the formation of…

molecules

Recall the typical size (order of magnitude) of atoms and small molecules

atoms and molecules are extremely small

• about 10^-10 m across

Explain the formation of simple molecular, covalent substances, using dot and cross diagrams, including:
a) hydrogen
b) hydrogen chloride
c) water
d) methane
e) oxygen
f) carbon dioxide

a) = 2 hydrogens
b)= hydrogen and chlorine
c) = two hydrogen and one oxygen
d)= one carbon, four hydrogen
e) = two oxygen
f)= one carbon two oxygen

Explain why elements and compounds can be classified as ionic

• found in most compounds containing metal and non metal atoms

• bonding = ionic bonds formed by the loss and gain of electrons to produce oppositely charged ions that attract one another

• structure = billions of ions held together in a lattice structure

Explain why elements and compounds can be classified as simple molecular (covalent)

• found in most non-metal elements and compounds

• bonding = covalent bonds formed when atoms share pairs of electrons

• structure = small, distinct groups of atoms

Explain why elements and compounds can be classified as giant covalent

• found in a few non-metal elements and some compounds of non-metals

• bonding = covalent bonds formed when atoms share pairs of electrons

• structure = billions of atoms held together in a lattice structure

Explain why elements and compounds can be classified as metallic

• found in all metals

• bonding = metallic bonds are the electrostatic attraction between positive metal ions and negative delocalised electrons

• structure = billions of ions held in a giant lattice structure of positive ions in a 'sea' of negative delocalised electrons

Explain the properties of typical covalent, simple molecular compounds limited to:

• a) low melting points and boiling points, in terms of forces between molecules (intermolecular forces)

• b) poor conduction of electricity

• a)- some forces of attraction between the molecules, but they are very weak in comparison (weak intermolecular forces) - doesn't take much energy to overcome these forces, so low melting / boiling points

• b)- simple molecular molecules have no overall charge and so cannot carry an electrical current. in a covalent bond, electrons are shared between two atoms. the strong forces between the negatively charged electrons and positively charged nuclei mean electrons cannot flow so do not carry a current

Recall that graphite and diamond are different forms of…

carbon, examples of giant covalent substances

Describe the structure of graphite

graphite:

• have huge three dimensional networks of carbon atoms linked by covalent bonds

• with three covalent bonds for each carbon atom

• this gives it a layered structure so not all electrons are held in covalent bonds - weak forces between layers of carbon

Describe the structure of diamond

diamond:

• have huge three dimensional networks of carbon atoms linked by covalent bonds

• with four covalent bonds for each carbon atom

Explain, in terms of structure and bonding, why graphite is used to make electrodes and as a lubricant, whereas diamond is used in cutting tools

graphite:

• sheets of carbon atoms in graphite are held together by weak forces of attraction

• these forces allow the layers to slide past each other, making it soft and useful as lubricant

diamond:

• very hard because it has a rigid network of carbon atoms in a tetrahedral arrangement

• joined by strong covalent bonds => this makes diamond useful for tools to cut things

Explain the properties of fullerenes including C₆₀ and graphene in terms of their structures and bonding

• graphene is made up of one single layer of carbon atoms only one atom thick

• the carbon atoms are held together by strong covalent bonds

• fullerenes = covalent molecules of carbon which have hollow arrangements

State an example of a fullerene and explain

• poly(ethene) = common polymer made of ethene monomers

• simple polymers consist of large molecules containing chains of carbon atoms

Explain the properties of metals, including malleability

malleable: (can be hammered without shattering) as when you hit a metal, the layers of ions slide over each other as the 'sea' of electrons hold these together so the metal changes shape without breaking

Describe the limitations of particular representations and models, including dot and cross

• shows how electrons are shared in covalent bonds

• however they do not show the structure formed and they suggest that the electrons in different atoms are different, when they are actually the same

Describe the limitations of particular representations and models, including ball and stick

• show which atoms are joined together and show the shape of the structure

• however they show the atoms too far apart and they are not really 'sticks' holding the atoms together

Describe the limitations of particular representations and models, including 2D and 3D representations

• show the metal ions held in a lattice and explains why it conducts electricity

• model does not show that the ions will be vibrating all the time

Describe most metals

• shiny

• usually solid at room temp.

• high mpt + bpt

• high density

• good conductors of electricity

Describe most non-metals

• low boiling points

• poor conductors of electricity

• poor thermal conductors

• brittle

• dull