C2.3 Properties of materials Flashcards
Explain how carbon is able to form different families of compounds
- Carbon is in group 4, so its atoms have 4 electrons in their outer shell and can form 4 covalent bonds
- A carbon atom can join with other carbon atoms to form chains and rings, as well as join with other elements to produce many different compounds
State and explain the properties of diamond in terms of its structure and bonding
- An allotrope of carbon
- Transparent + very hard
- Giant covalent structure in which each carbon atom is covalently bonded to 4 other carbon atoms
- Has many covalent bonds (strong) and so has a very high melting point + very hard
- Used in dental drills
- All outer electrons in its atoms are shared (forming covalent bonds) so it has no delocalised electrons, and so it doesn’t conduct electricity
Define allotropes
Forms of an element in the same state but with different atomic arrangements
State and explain the properties of graphite in terms of its structure and bonding
- An allotrope of carbon
- Grey-black + soft
- Giant covalent structure in which each each carbon atom is covalently bonded to just three other carbon atoms
- Which means that one electron in the outer shell of each atom is not involved in bonding and becomes delocalised instead
- the delocalised electrons in graphite are free to move through structure, so graphite conducts electricity even though it is a non-metal
- Has layered structure - atoms in each layer form interlocking hexagons like knots in chicken wire
- Many strong covalent bonds in layers give graphite a very high melting point
- Although, forces between each layer are weak, so layers can slide over each other easily - this is why graphite is slippery (so some of graphite tip of pencil rubs off on paper)
State and explain the properties of graphene in terms of its structure and bonding
- carbon allotrope
- resembles single layer of graphite
- almost transparent, extremely strong, conducts electricity
State and explain the properties of fullerenes in terms of its structure and bonding
- large family of carbon allotropes in which molecules are shaped like balls or tubes
Nanotube - A sheet of graphene rolled into a tube
- Strong - used to reinforce some sports equipment
Buckyball - A sheet of graphene closed to make a hollow ball, but carbon atoms may be in pentagons or hexagons
- Potential uses as lubricants, with molecules acting like tiny ball bearings
- Small size allows them to pass through cell membranes, and so they might one day deliver medical drugs directly to cells
Explain what happens during change of state of a substance (in terms of energy transfer )
- when melting or boiling, forces of attraction between particles are overcome
- some (solid to liquid) or all (remaining bonds from liquid to gas) of the bonds between its particles break.
- depending on substance, these will be different types of bonds
- the stronger the bonds and the more of them there are, the more energy must be transferred from the surroundings to break them
- if they have many strong bonds they have high melting and boiling points
- Bonds form when a substance condenses (some from gas to liquid) or freezes (many from liquid to solid)
- when chemical bonds form stored chemical energy it transferred to the surroundings, usually by heating
Use ideas about the relative strength of chemical bonds and intermolecular forces to explain the different temperatures at which changes of state occur
- to decide if a substance is likely to have low/high melting/boiling point, you need to know the types of bonds involved in state changes.
Type of substance - bonds involved in state changes - relative strength - examples of substances
Metal - metallic bonds - strong - iron, mercury
Ionic compound - ionic bonds - strong - sodium chloride
Giant covalent structure - covalent bonds - strong - diamond, silica
Simple molecule - intermolecular forces - weak - oxygen, water wax
Metals, ionic compounds and giant covalent substances are usually in solid state at room temperature. Simple molecular substances are in liquid/gas state at room temp, or in the solid state but easily melted.
Explain why atoms themselves do not have the bulk properties of these materials
- individual atoms don’t have physical properties of the materials they form
- e.g. a single copper atom cannot conduct electricity
- any property that results from behaviour of many atoms acting together is called a bulk property
Explain some bulk properties of metals
- metals are malleable even though metallic bonds are strong as the particles in the substance can change their position in the lattice structure
- 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, but as the delocalised electrons are
free to move, overall no bonds are broken - metals conduct electricity in the solid and liquid states as their delocalised electrons are free to move through the lattice.
Explain some bulk properties of giant covalent structures
- contain lots of atoms held together in a giant lattice by strong covalent bonds. If a large enough force is applied many covalent bonds break at once and the substance breaks
- cannot conduct electricity as they have no delocalised electrons
Explain some bulk properties of ionic compounds
- oppositely charged ions held together in a giant lattice by strong ionic bonds
- many of those ionic bonds break at once if a large enough force is applied, and so the ionic substance is brittle and breaks
- Ions are free to move when the ionic compound is in the liquid state or dissolved in a solvent such as water or when molten, but not when the ionic compound is in the solid state
Explain some bulk properties of simple molecules and polymer molecules
- are attracted to each other by weak intermolecular forces, which are easily broken
- if these substances are in the solid state and their molecules are arranged in a lattice, they may be brittle (e.g. iodine crystals)
- if they aren’t arranged in a lattice, the substance may be soft or flexible (e.g. wax, particularly when it’s warm)
- simple molecules and most polymers don’t conduct electricity as they have no delocalised electrons
Recall the relative size of nanoparticles
1nm - 100nm
Bigger than a methane molecule, smaller than a red blood cell
Describe the surface area to volume relationship for different-sized particles and describe how this affects properties
- nanoparticulate materials have different properties to the same properties in bulk
- some of these properties are due to the very small size of nanoparticles
- many properties of nanoparticles are due to their very large SA:V compared with the same substance in bulk
