Structure

StructureMagnesium has metallic bonding.(i)Draw a diagram to show what is meant by metallic bonding. Label the diagram.[2] (ii) Why is magnesium a good conductor of electricity?[1]

(i)positive ions/cations and negative electrons Can be described in words only for both marks2(ii)contain free/mobile/delocalised electrons 1

Draw how you think the ions are arranged insolid sodium chloride.Draw a dot-cross diagram for sodium chlorideSodium chloride has a high melting point. ExplainDraw what you think happens when sodium chloridedissolves in waterWhat is needed for a substance to be able toconduct electricity?Explain why solid sodium chloride doesnt conduct whensolid but does when molten or in solution.Draw how you think the ions are arranged insolid sodium chloride.Draw a dot-cross diagram for sodium chlorideSodium chloride has a high melting point. ExplainDraw what you think happens when sodium chloridedissolves in waterWhat is needed for a substance to be able toconduct electricity?Explain why solid sodium chloride doesnt conduct whensolid but does when molten or in solution.Sodium Chloride - an Ionic Crystal

What you need to know:Sodium chloride is an ionic lattice.

Each chloride ion is surrounded by six sodium ions. And vice versa.

The ions are held together by strong electrostatic forces which require much energy to break. Therefore NaCl has a high melting point.You must be able to draw NaCl at least:

The bonding is ionic.

Will ionic compounds conduct electricity when solid?No the ions are fixed in position.When molten or in solution the ions become free to move so NaCl will then conduct electricity

SolubilityIonic compunds only dissolve in polar solvents like water.Use p 69 in your text book to help you explain why. Draw a diagram in your answer.Diamond - A giant covalent crystal

Diamond is the hardest known natural material and one of the two best known forms (or allotropes) of carbon, whose hardness and high dispersion of light make it useful for industrial applications and jewellery.

Draw a dot cross diagram to show how 1 C atom can covalently bond to 4 other C atoms.What will the shape be?What will you expect the melting point to be?Why?What will you expect the solubility in water to be?Why?What will you expect the electrical conductivity to be?Why?Draw a dot cross diagram to show how 1 C atom can covalently bond to 4 other C atoms.What will the shape be?What will you expect the melting point to be?Why?What will you expect the solubility in water to be?Why?What will you expect the electrical conductivity to be?Why?What you need to know:Diamonds consist of tetrahedrally bonded carbon atoms, i.e. each carbon is covalently bonded to 4 others in a regular arrangement.

You need to be able to drawone unit

The many very strong covalent bonds require a lot of energy to break so diamond has a high melting point.

The tetrahedral arrangement of carbons held by strong covalent bonds makes diamond hard.

It does not conduct electricity as there are no free electrons or ions.

It does not dissolve in polar or non-polar solvents as the covalent bonds in the lattice are too strong to be broken by any solvents.Graphite - Another giant covalent crystal

With anomalous properties!Most people first encounter graphite as pencil lead (in fact it's not lead, it's graphite).

In its pure glassy (isotropic) synthetic form carbon fibre, is an extremely strong, heat-resistant (to 3000 C) material, used in re-entry shields for missile nosecones, solid rocket engines, high temperature reactors and brake shoes.

Draw a dot cross diagram to show how 1 C atom can covalently bond to 3 other C atoms.What will the shape be?What will you expect the melting point to be?Why?What will you expect the solubility in water to be?Why?What will you expect the electrical conductivity to be?Why?Draw a dot cross diagram to show how 1 C atom can covalently bond to 3 other C atoms.What will the shape be?What will you expect the melting point to be?Why?What will you expect the solubility in water to be?Why?What will you expect the electrical conductivity to be?Why?What you need to know:Each carbon atom is covalently bonded to three other surrounding carbon atoms. These bonds are strong so graphite has a high melting point.

The flat sheets of carbon atoms are bonded into hexagonal structures which exist in layers.

Different layers are connected together by weak van der Waals forces. Therefore, layers of it can slip over each other making it soft.

Graphite can be used as a lubricant as the layers can slip over one another.

Unlike diamond, graphite is an electrical conductor. Delocalised electrons between the layers are free to move in the direction of the current.Iodine - a simple molecular crystal

Iodine (from the Greek word Iodes, meaning "violet"), is chemically the least reactive of the halogens.

Iodine is primarily used in medicine, photography and dyes. It is required in trace amounts by most living organisms.

As with all other halogens (members of Group VII in the Periodic Table), iodine forms diatomic molecules, and hence, has the molecular formula of I2.Iodine is a simple molecular substance.What type of intermolecular forces do you expect there to be in iodine? Predict (with reasons) the melting point,electrical conductivity and solubility in water of iodine.What you need to know:Iodine is a dark grey crystalline solid with a purple vapour.

The iodine atoms within each molecule are pulled closely together by the strong covalent bond.

The van der Waals attraction between the molecules is much weaker and are easily broken when heat is applied. This is why the melting point of iodine is low.

Iodine does not conduct electricity as there are no free ions or electrons.Iodine is soluble in non-polar solvents such as hexane because Van der Waals forces form between the molecules and the solvent.The table below shows the structures and some properties of sodium chloride and graphite in the solid state. Explain these properties in terms of bonding and structure. [7]

substancesodium chloridegraphiteStructure

electricalconductivity of solidpoorgoodmelting and boilingpointhighhighsolubility in watergoodinsoluble

General

NaCl: ionic/has ionic bonds (1)Beware of contradictions for this mark, especially reference to intermolecular forces.Ignore atoms.graphite: covalent/giant molecular/macromolecular (1)Ignore van der Waals, intermolecular, molecules

ConductivityNaCl:ions cannot move/no free ions (or electrons) /mobile ions only in solution or when molten (1)graphite:delocalised electrons/ free electrons (between layers)/ electrons conduct (1)Ignore lone pair

melting pointboth graphite and NaCl:bonds are strong/bonds difficult to break /large amount of energy is needed to break bonds (1 for each)

solubilityNaCl:Water is polar/water has a dipole/ions interacts with water molecules (1)Graphite:no interaction with water/no intermolecular forces with water/graphite is non-polar (1)QWC:At least 2 complete sentences in whichthe meaning is clear. (1)[8]Jan 20016 (a) With the aid of diagrams, describe the structure of, and bonding in, crystals of sodium chloride, graphite and magnesium. In each case, explain how the melting point and the ability to conduct electricity of these substances can be understood by a consideration of the structure and bonding involved. (23 marks)Sodium chlorideIonic bondingGiant ionic latticeDiagram showing alternating +/- ionsHigh melting pointStrong electrostatic attraction between oppositely charged ions.Put in a lot of energy to overcomeDoesnt conduct when solidNo mobile ions/charged particlesDoes conduct when molten/solutionIons free to move

GraphiteCovalent bonding.Macromolecular/giant covalent structureDiagramHigh mpStrong covalent bonds between atomsMust put in a lot of energy to break.Conduct electricityFree/mobile/delocalised electronsMagnesiummetallic structure and/or bondingDiagram with labelled +ve ions and delocalised electrons.High mp Strong metallic bondMust put in a lot of energy to breakConducts electricityFree/mobile/delocalised electrons