C2 - Bonding, structure and properties of matter Flashcards
what are ions and how are they formed?
Ions are charged particles that are formed when electrons are transferred
which groups are the most likely to form ions?
groups 1, 2, 6 and 7
what are cations?
positive ions
what are anions?
negative ions
what are three types of bonding?
ionic, covalent and metallic
what happens in ionic bonding?
when a metal and a non-metal react together, the metal atom loses electrons to form a positively charged ion and the non-metal gains these electrons to form a negatively charged ion. These oppositely charged ions are strongly attracted to one another by electrostatic forces. This attraction is called an ionic bond
what structure do ionic compounds form?
a giant ionic lattice
what are the properties of ionic compounds?
they all have high melting and boiling points due to the many strong bonds between the ions.
When they’re solid, the ions are held in place, so the compounds can’t conduct electricity, however when they melt the ions are free to move and they’ll carry electric current.
some ionic compounds dissolve in water. The ions separate and are all free to move in the solution, so they’ll carry electric current
what is an empirical formula?
the empirical formula of a substance is the simplest whole number ratio of the atoms of each element present
what are the three steps to working out an empirical formula?
- look at the diagram to work out what ions are in the compound
- work out what charges the ions will form
- balance the charges so the charge of the empirical formula is zero
what makes covalent bonds very strong?
the positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces
what are dot and cross diagrams useful for? what are their drawbacks?
Dot and cross diagrams are useful for showing which atoms the electrons in a covalent bond come from, but they don’t show the relative sizes of the atoms, or how they are arranged in space
how can you find the molecular formula of a simple molecular compound from a diagram?
by counting up how many atoms of each element there are
what are simple molecular substances?
small molecules containing a few atoms joined together by covalent bonds
what is the formula for methane?
CH4
what is the formula for ammonia?
NH3
what are the properties of simple molecular structures?
- held together with strong covalent bonds
- weak intermolecular forces
- low melting and boiling point - most molecular substances are gases or liquids at room temperature
- don’t conduct electricity
as molecules get bigger, does the strength of the intermolecular forces increase or decrease? Do the melting and boiling points increase or decrease?
increase, increase
what are three structures that have covalent bonds?
simple molecular substances, polymers and giant covalent substances
what are polymers?
long chains of repeating units
what do you do instead of drawing out a whole long polymer molecule, which can contain thousands or even millions of atoms?
you can draw the shortest repeating section (repeating unit)
how do you find the molecular formula of a polymer?
write down the formula of the repeating unit in brackets and put an ‘n’ outside
are the intermolecular forces between polymer molecules smaller or larger than between simple molecular substances?
larger
what state are most polymers at room temperature?
solid
are the intermolecular forces between polymer molecules stronger or weaker than ionic and covalent bonds?
weaker
are giant covalent structures macromolecules or micromolecules?
macromolecules
what are some properties of giant covalent structures?
- very high melting and boiling points as a lot of energy is needed to break the strong covalent bonds
- they don’t contain charged particles so they don’t conduct electricity, even when molten (with some exceptions)
what are three examples of giant covalent structures?
Diamond, graphite and silicon dioxide
describe the structure of diamond
each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure
describe the structure of graphite
each carbon atom forms 3 covalent bonds to create layers of hexagons. Each carbon atom also has one delocalised electron
what does silicon dioxide (sometimes called silica) make up?
sand. Each grain of sand is one giant structure of silicon and oxygen.
what are allotropes?
different structural forms of the same element in the same physical state
name 4 allotropes of carbon
diamond, graphite, graphene and fullerenes
are there covalent bonds between the layers of graphite? What does this mean?
there are no covalent bonds between the layers of carbon, which means that they’re only held together weakly so they’re free to move over each other. This makes graphite soft and slippery, so it’s ideal as a lubricating material
can graphite conduct heat and electricity? why?
graphite can conduct heat and electricity because each carbon atom only makes three bonds, which leaves one delocalised electron for each carbon atom. These are free to move throughout the structure and so can conduct heat and electricity.
what is graphene?
one layer of graphite
what are the properties of graphene?
- the network of covalent bonds makes it very strong
- it’s light, so it can be added to composite materials to improve their strength without adding too much weight
- it contains delocalised electrons which means it can conduct electricity
what are fullerenes?
molecules of carbon joined together to form closed tubes or hollow balls
what is buckminsterfullerene?
the first fullerene to be discovered. It’s got the molecular formula C60 and forms a hollow sphere
what can fullerenes be used for?
fullerenes can be used to ‘cage’ other molecules. The fullerene structure forms around another atom or molecule, which is then trapped inside. This could be used to deliver a drug into the body.
fullerenes have a large surface area, so they make great industrial catalysts - individual catalyst molecules could be attached to the fullerene.
fullerenes also make great lubricants.
what are nanotubes?
tiny carbon cylinders that can be formed by fullerenes
is the ratio between the length and diameter of nanotubes high or low?
high
what are the properties of nanotubes?
- can conduct both electricity and thermal energy
- have a high tensile strength (don’t break when they are stretched)
- nanotubes can be used in electronics or to strengthen materials without adding much weight, such as in tennis racket frames
what is nanotechnology
technology that uses very small particles such as nanotubes
describe the structure of metals
- metals consist of a giant structure
- the electrons in the outer shell of the metal atoms are delocalised. There are strong forces of electrostatic attraction between the positive metal ions and the shared negative electrons
- these forces of attraction hold the atoms together in a regular structure and are known as metallic bonding
what is responsible for producing all the properties of metals?
the delocalised electrons
what are the properties of metallic bonds?
- very strong
- solid at room temperature (except mercury)
- good conductors of electricity and heat
- most metals are malleable
why are most metals solid at room temperature?
the electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong, so a lot of energy needs to be overcome in order to melt them.
why are metals good conductors of electricity and heat?
the delocalised electrons can carry electrical current and thermal energy through the whole structure
why are most metals malleable?
the layers of atoms in a metal can slide over each other, making metals malleable - this means that they can be bent or hammered or rolled into flat sheets
what is harder, alloys or pure metals?
alloys
what is an alloy?
a mixture of two or more metals or a metal and another element
why are alloys harder than pure metals?
different elements have different sized atoms, so when another element is mixed with a pure metal, the new metal atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other, making alloys harder than pure metals
what are the three states of matter?
solid, liquid, gas
what does which state a substance is at a certain temperature depend on?
how strong the forces of attraction are between the particles of the material
what three things does the strength of the forces of attraction between the particles depend on?
- the material (the structure of the substance and the type of bonds holding the particles together)
- the temperature
- the pressure
what is particle theory?
a model that explains how the particles in a material behave in each of the three states of matter by considering each particle as a small, solid, inelastic sphere
describe the structure of solids
- strong forces of attraction between particles, which holds them close together in fixed positions to form a very regular lattice arrangement
- particles don’t move from their positions, so all solids keep a definite shape and volume, and don’t flow like liquids
- the particles vibrate about their positions - the hotter the solid becomes the more they vibrate
describe the structure of liquids
- a weak force of attraction between the particles. They’re randomly arranged and free to move past each other, but they tend to stick closely together
- liquids have a definite volume but don’t keep a definite shape, and will flow to fill the bottom of a container
- the particles are constantly moving with random motion. The hotter the liquid gets, the faster they move. This causes liquids to expand slightly when heated
describe the structure of gases
- very weak forces of attraction between particles - they’re free to move and are far apart. The particles in gases travel in straight lines.
- don’t keep a definite shape or volume and will always fill any container
- the particles move constantly with random motion. The hotter the gas gets, they faster they move. Gases either expand when heated, or their pressure increases
what are the drawbacks of particle theory?
- particles aren’t solid or inelastic and they aren’t spheres - they’re atoms, ions or molecules
- doesn’t show the forces between the particles, so there’s no way of knowing how strong they are
what do state symbols tell you?
the state of a substance in an equation
what are the state symbols?
(s) - solid
(l) - liquid
(g) - gas
(aq) - aqueous
what does aqueous mean?
dissolved in water
