C2.3 (properties of metals)

• name some different forms of carbon

  diamond, graphite, graphene and fullerenes
• why can carbon form so many different compounds?

  Carbon is in group 4 so its atoms have 4 electrons in their outer shells and form 4 covalent bonds. carbon atoms can join to other carbon atoms to form chains and rings , and the carbon atoms in these structures can form covalent bonds with other elements such as hydrogen and oxygen which produces many different compounds
• what are allotropes?

  Different forms of an element in the same state but with different atomic arrangements.
• name 2 allotropes of carbon?

  Diamond and graphite

  diamond is transparent and very hard, but graphite is grey/black and soft. they are different due to their structures and bonding
• what does diamond exist as?

  A giant covalent structure in which each carbon atom is covalently bonded to 4 other carbon atoms. diamond has a lot of very strong covalent bonds which means that diamond has a very high melting point and is very hard. all outer electrons in its atoms are shared and they all form covalent bonds
• give 2 other facts about diamond

  its hardness makes it suitable for tips of dental drills and diamond has no delocalised electrons so does not conduct electricity
• What does graphite exist as?

  a giant covalent structure in which each carbon atom is covalently bonded to only 3 other carbon atoms. this means that 1 electron in the outer shell is not involved in bonding and becomes delocalised instead.
• how does graphite conduct electricity?

  The delcocalised electrons from each outer shell are free to move through the structure so it conducts electricity even though it is a non metal
• describe the structure of graphite

  Graphite has a layered structure. the atoms in each layer form interlocking hexagons like chicken wire. the many strong covalent bonds in the layers give graphite a very high melting point. However the forces between layers are very weak so layers can slide over each other easily, which is why graphite is good to use in pencils
• why does graphite have delocalised electrons but diamond does not?

  Carbon atoms in graphite only form 3 covalent bonds so there is one electron not needed in bonding, whereas carbon atoms in diamond form 4 bonds so there are no free electrons
• what is graphene?

  A carbon allotrope that resembles a single layer of graphite. it is almost transparent, extremely strong and conducts electricity. scientists are looking at new ways to use graphene as its properties are very interesting
• what are fullerenes?

  They form a large family of carbon allotropes in which the molecules are shaped like tubes or balls.
• what is a nanotube?

  It resembles a sheet of graphene rolled into a tube, nanotubes are strong and used to reinforce some sports equipment
• What is a buckyball?

  Resembles a sheet of graphene closed to make a hollow ball, but the carbon atoms may be in pentagons as well as hexagons. Buckyballs have potential uses as lubricants as their molecules act as tiny ball bearings. their small size also allows buckyballs to pass through cell membranes so they may one day be used to deliver medical drugs directly to cells
• what happens when a substance melts or boils?

  Forces of attraction between its particles are overcome, some or all of the bonds between its particles break.
• how many bonds break when going from the solid to the liquid to the gas state?

  Some bonds break, and all remaining bonds break going from the liquid to the gas state
• what bonds can be present in substances?

  Metallic bonds, ionic bonds, covalent bonds and intermolecular forces
• what happens when bonds are stronger?

  The stronger the bonds and the more of them there are, the more energy that must be transferred from the surroundings to break them. substances have high melting points if they have many strong bonds in the solid state and substances have high boiling points if they have many strong bonds in the liquid state.
• when do bonds form when a substance condenses or freezes?

  some bonds form going from the gas to the liquid state and many bonds form going from the liquid to the solid state
• where is energy transferred to when bonds form?

  Stored chemical energy is transferred to the surroundings (usually by heating) when chemical bonds form
• how do you predict states?

  The melting point of bromine is -7°c and its boiling point is 59°c. predict its state at 25°c

  1: is the temperature below the melting point? if it is then the substances will be in the solid state. 25°c is above -7°c so it is not in the solid state

  2: is the temperature above the boiling point? If it is then the substance will be in the gas state. 25°c is below 59°c so it is not in the gas state

  Therefore bromine must be in the liquid state at 25°c
• how can you decide if a substance has a high or low melting or boiling point?

  By knowing the types of bonds involved in state changes
• what bonds are involved in state changes in metals?

  Metallic bonds, strong in strength and examples are iron or mercury
• what bonds are involved in state changes with ionic compounds?

  Ionic bonds, strong in strength and examples are sodium chloride
• what bonds are involved in state changes with giant covalent structures?

  Covalent bonds, strong in strength and examples are diamond or silica
• what bonds are involved in state changes with simple molecules?

  Intermolecular forces, weak in strength and examples are oxygen, water and wax
• what state are metals, ionic compounds and giant covalent structures in at room temperature?

  Metals: Solid , Ionic compounds: Solid

  Giant covalent structures: Solid
• what state are simple molecular substances in at room temperature?

  Liquid or gas state, or in the solid state but easily melted
• what is sublimation?

  Changing directly from the solid to the gas state below their melting and boiling points
• how does iodine sublime?

  It exists as simple molecules that are attracted to each other by weak intermolecular forces. the molecules are packed in a regular way in the solid state and form shiny black crystals. iodine molecules easily separate from one another at room temperature which forms a purple vapour
• what is the opposite of sublimation?

  Deposition
• what happens to a brittle substance when an external force is applied?

  It cracks or breaks
• what happens to a malleable substance when an external force is applied?

  They change shape without cracking or breaking.
• what does the difference depend on when looking at malleable and brittle substances?

  It all depends on how easily the particles in the substance can change their positions in the lattice structure
• how come metals are malleable even though their metallic bonds are strong?

  Metal ions are held in a lattice by forces that attract them to a sea of delocalised electrons. when a large enough external force is applied, layers of metal ions slide over one another. however, since the delocalised electrons are free to move, no bonds are broken overall.
• what can layers of ions do in metals?

  Slide over each other
• what happens if a large enough force is applied to giant covalent structures?

  Many covalent bonds break at once and the substance breaks
• what are ionic compounds usually , brittle or malleable?

  Brittle, due to the ionic bonds breaking in a compound
• what are simple molecules and polymer molecules attracted to each other by?

  Weak intermolecular forces that are easily broken, if these substances are in the solid state and their molecules are arranged in a lattice then they may be brittle. an example of this would be iodine crystals and some polymers
• what happens if molecules are not arranged in a lattice?

  The substance may be soft or flexible , wax is like this especially when it is warm