3Comparing the properties of metals and non-metals Good conductors of electricityPoor conductors of electricityGood heat conductorsPoor heat conductorsMalleable (can be moulded into shape)Non-malleable (brittle in their solid form)Ductile (can be pulled into wires)Non-ductileShiny (when freshly cut)Not usually shinyMany have high melting pointsLow melting pointMany have high boiling pointsLow boiling pointGCSE Additional ScienceChapter 7
4Metals GCSE Additional Science Chapter 7 The key to understanding a metal’s properties lies in its structurepositive ionsA metal structure is an ordered pattern of positive ions in a ‘sea’ of negative electrons.free electronsDuctilityElectrons act as a type of lubricant between the layers of ions. This explains why it’s possible to pull metals to form wires.Electrical ConductorsConnecting the sides to a battery makes the electrons move from the negative side towards the positive – this is the flow of current.Explaining theproperties ofMETALSGCSE Additional ScienceChapter 7Melting PointThe strength of metallic bonds depends on the number of outer electrons in the atoms (the more outer electrons there are , the higher the melting point).
5Alloys Metallic Glass GCSE Additional Science Chapter 7 Stainless steel is an example of an alloy used to make saucepans and cutlery.Some modern alloys can recover their shape after bending. These are used in frames for glasses. They are a type of ‘smart material’ called shape-memory alloy.Metallic GlassAs mentioned previously, most solids have a structure that shows a regular pattern but it’s possible to form metals that show less of a pattern – these are the metallic glasses.GCSE Additional ScienceChapter 7Metallic glasses are three times as strong as steel and ten times more flexible, making them ideal for use as golf club-heads.
6BONDING Ionic Structures Sodium chloride is formed when atoms of sodium bond with atoms of chlorine.Cl-Na+GCSE Additional ScienceChapter 7Sodium atom (Na) [2.8.1]Sodium ion (Na+) [2.8]Chlorine atom (Cl) [2.8.7]Chloride ion (Cl-) [2.8.8]Both atoms are trying to achieve a full set of outer electrons. They can do this if the sodium atom gives its outer electron to the chlorine atom.We now have a sodium ion Na+, and a chloride ion Cl-.
7BONDING Ionic Structures Na+Chloride ion (Cl-) [2.8.8]Sodium ion (Na+) [2.8.]Cl-GCSE Additional ScienceChapter 7Sodium chloride (salt)
8BONDING Ionic Structures So there are two types of ion:-Positive ion (cation) – the atom has lost an electron or electrons.Negative ion (anion) – the atom has gained electron(s).The ions attract and the attraction is ionic bonding.BONDING Ionic StructuresThe oppositely charged ions attract each other. They cluster around each other (six Cl- around each Na+ and vice versa) to make an ionic giant structure.Six Chloride ions cluster around one Sodium ionGCSE Additional ScienceChapter 7Six Sodium ions cluster around one Chloride ionMolecular structure of Sodium Chloride(Click molecule to show animation)
9Properties of Ionic Compounds PROPERTYDUE TOHigh melting pointStrong electrostatic forces of attraction between the ions. A lot of energy is needed to break them.Solid ionic compounds do not conduct electricity.The ions are held in fixed positions, and are not free to move.Molten ionic compounds conduct electricity.Melting has separated the ions so that they can move past each other.GCSE Additional ScienceChapter 7
10BONDING Covalent Bonding Non-metal atoms bond with each other by sharing outer shell electrons.This is called COVALENT BONDING.Covalent bonding can produce:Small molecules of elements, e.g. H2Small molecules of compounds, e.g. HClGCSE Additional ScienceGiant molecules of elements, e.g. diamond and graphiteChapter 7Giant molecules of compounds, e.g. SiO2
11BONDING Covalent molecules Some elements form covalent compounds. This happens as atoms share electrons.HClGCSE Additional ScienceChlorine atom (Cl) [2.8.7]Hydrogen atom (H) Chapter 7Molecule of hydrogen chloride (HCl)Hydrogen has the electron pattern of helium, and chlorine has the electron pattern of argon.This is written as H-Cl, where the ‘-’ represents a covalent bond (pair of shared electrons).
12Properties of molecular covalent compounds Melting pointsLow(attraction between molecules is weak)Physical state at room temperatureGases or liquids with low boiling points or solids with low melting points(weak forces of attraction between molecules)Electrical conductivityDo not conduct electricity(the molecules have no charge)Solubility in waterMost are insoluble in waterGCSE Additional ScienceChapter 7
13An exercise to recognise atomic or covalent bonds An exercise to recognise atomic or covalent bonds. (Only the outer shell is shown in the diagrams)HCa2+ F-2HOioniccovalentClcovalentMg2+ Cl-2covalentionicOGCSE Additional ScienceChapter 7NHCuCu O2-covalentionicShow the answers
14Comparing the properties of graphite and diamond Giant Covalent StructuresComparing the properties of graphite and diamondSome covalent molecules exist as giant covalent structures. These have a high melting point because all the atoms are held by strong covalent bonds. Graphite and diamond are examples of giant covalent structures made up of a collection of carbon atoms only.PROPERTYAppearanceTransparent crystalsGrey/ black shiny solidHardnessIncredibly hard – used for cutting glass and in drill bits for drilling through rocks in the oil industry.Very soft – used as a lubricant. Also used to make pencils.ConductivityElectrical insulatorA non-metal that conducts electricity. Used for making electrodes.Melting pointVery high – over 3500°C.Very high – over 3600°C.DiamondGraphiteGCSE Additional ScienceChapter 7
15An explanation of the properties of diamond and graphite Graphite has layers formed from hexagonal rings – these layers can slide over each other, and this is why it is used as a lubricant.Every atom is bonded to 4 other atoms. Every outer electron has its role to play in the covalent bonding that happens here. The result is a very rigid structure. As there are no free electrons, it doesn’t conduct electricity and it’s a good conductor of heat.GCSE Additional ScienceChapter 7Every carbon atom bonds strongly to other carbon atoms by three covalent bonds. The fourth outer electron in each atom is free to move, and this is what makes graphite a good conductor.
16The future, and other forms of carbon Whilst experimenting with Fullerene C60, it was found that other structures of carbon could be formed. One of them is seen below:Fullerene C60Carbon NanotubeThe carbon atoms are bonded covalently into a football shape.The nanotube is like rolled graphite.It conducts electricityIt’s very small – 10,000 times thinner than a human hairCrystals can be grown inside itThey may solve the problem of how to produce smaller circuits, where they might replace wires.GCSE Additional ScienceChapter 7NanotubeHuman hair