C2 (bonding, structure, the properties of matter) Flashcards
how does ionic bonding work? use lithium, a metal, and fluorine, a non-metal, in your example:
- neither lithium or fluorine have a full outer energy level; lithium has 1 electron in its outer energy level, fluorine has 7.
- lithium can react to lose one electron to gain a full outer energy level, and fluorine can use this electron to fill its outer energy level. now both fluorine and lithium are stable ions.
- lithium lost an electron, and so has a charge of 1+, and fluorine gained an electron, and so has a charge of 1-.
- in the end, both atoms have the structure of a noble gas.
between which elements does ionic bonding occur?
ionic bonding occurs between metal and non-metals. this means they are oppositely charged ions, and so are attracted to each other by electrostatic force, to form an ionic compound
- this force is an ionic bond, which is really strong
how does covalent bonding occur? use two hydrogen atoms in your example:
- hydrogen atoms have only one electron in their outer shells, and they require two.
- the two hydrogen atoms overlap their electron shells, and now both atoms have two electrons in their outer electron shells.
- these two hydrogen atoms are now stable
- covalent bonding only occurs between two non-metal atoms
- sharing electrons, by overlapping outer shells
what are displayed formulas, and what are its pros and cons?
have the elemental symbol of each element, joined by a single line representing the covalent bond
pro:
can be used to draw big molecules that would take too long or be too complicated to draw as dot and cross diagrams
cons:
don’t show anything about the 3d shape of the molecule
what are the formulae for ammonia and methane?
- ammonia = NH3
- methane = CH4
describe metallic bonding:
- occurs when metals bond with other metals
- metals are giant structures of atoms, arranged in a regular pattern. when these atoms are together, they give up their electrons in their outer shells, and share them with all the other atoms DELOCALISED ELECTRONS
- these atoms all become positive ions
- there is now a strong electrostatic attraction between the positive ions and the negative electrons, and this holds everything together in a regular structure
- ‘sea of electrons surrounding a positively charged lattice’
what is an ionic compound?
giant structure of ions. held together by strong electrostatic forces of attraction between oppositely charged ions (they alternate). these forces act in all directions in the lattice, and this is called ionic bonding.
what are the limitations of using different diagrams to represent ionic compounds?
- dot and cross:
a: dots to represent one atom’s electrons, crosses to represent the other. very clearly shows where the electrons are coming from.
d: don’t tell us about the shape of the molecule, or the 3D arrangement of electrons. - 2D stick diagram:
d: can’t tell which electron in the covalent bond came from which atom. give us no idea of outer electrons that aren’t in bonds. do not accurate info on the shape of the molecule. - 3D stick diagram:
a: shows shape of the molecule. - ball and stick diagram:
a: we can clearly see the ions in 3D.
d: the ions are shown as widely spaced, when in reality, they’re packed together. gives impression that structure is small. - space filling diagramL
a: gives better idea of how closely packed the ions are.
d: can be difficult to see the 3D packing. gives impression that the structure is quite small.
what characteristics does an ionic lattice give metals?
this means that metals are incredibly strong, have high melting and boiling points (solid at room temperature), and are good conductors of electricity and heat (delocalised electrons can carry heat and electricity through the metal).
- also malleable (as they’re such a regular structure, the different layers can slide over one another) - the case for PURE METALS, as all the electrons are regular shapes
define malleable:
a malleable object can be easily bent or hammered into different shapes
why are alloys so strong?
- alloys contain two or more different elements, with different sized atoms (e.g. steel)
- either mix together two different metals, or a metal and a non-metal
- these different sized atoms disrupt the metal’s regular structure, and means that the atoms can no longer easily slide over one another, making the alloy much harder than pure metal
what are the properties of metals and alloys?
- metals have giant structures of atoms with strong metallic bonding. therefore most metals have high melting and boiling points.
- in pure metals, atoms are arranged in layers, making the metal easily bent and shaped.
- good conductors of electricity as the delocalised electrons in the metal carry electrical charge through it. this goes the same for thermal energy.
what do ionic compounds form?
- they form giant ionic lattices. every positive ion is surrounded by a negative ion, and vice versa.
- giant ionic lattices are 3d, and have very strong forces of attraction between the ions (ELECTROSTATIC FORCES = ionic bonds)
what are the properties of ionic compounds?
- very high melting and boiling points (strong ionic bonds require a lot of heat energy to break)
- they cannot conduct electricity when they’re solids, as the ions cannot move (the electrostatic forces lock them in place). however, molten or dissolved ionic compounds can conduct electricity, as charged particles (either ions/electrons) can move
- WHEN IONIC COMPOUNDS CONDUCT ELECTRICITY, IT’S THE IONS THAT MOVE, NOT THE ELECTRONS!
what is the formula for a sodium ion and a chloride ion forming an ionic compound?
- a sodium ion has a 1+ charge
- a chloride ion has a 1- charge
- together, the charges cancel each other out, forming NaCl
what is the formula for a magnesium ion and a chloride ion forming an ionic compound?
- magnesium ion has a 2+ charge
- chloride ion has a 1- charge
- therefore, to balance out the 2+ charge, we need two chloride ions: MgCl2
how would you calculate the formula for a calcium hydroxide ionic compound?
COMPLEXT CALCULATIONS
- hydroxide ion has a OH - (1-) charge
- calcium ion has a 2+ charge
- for each calcium, we need two hydroxide ions: Ca(OH)2
how do you calculate the formula for a aluminium sulfate ionic compound?
COMPLEX CALCULATIONS
- aluminium ion has a 3+ charge
- sulfate ion has a SO4 2- (2-) charge
- we need to find the lowest multiple 2 and 3 have in common: 6. to get a positive 6 charge, we need 2 aluminium ions, and to get a negative 6 charge, we need 3 of the sulfate ions
- the overall formula would be: Al2 (SO4) 3
what is the formula for a hydroxide ion?
OH -
what is the formula for a sulfate ion?
SO4 2-
what is the formula for a nitrate ion?
NO3 -
what is the formula for the carbonate ion?
CO3 2-
what is the formula for the ammonium ion?
NH4 +
what are the properties of simple covalent molecules?
- strong covalent bonds, so a lot of energy is needed to break apart any particles covalently bonded to each other
- low melting/boiling point, as we only need to break the intermolecular forces, which are weak. however, the more of these forces a substance has, the stronger the attraction is, despite their individual weakness
- don’t conduct electricity as there are no free charged particles
what is a polymer, and what are their properties?
- each giant polymer molecule is made up of smaller molecules, called monomers.
- a single polymer is strong, as its connecting covalent bonds are strong. however, to break up multiple polymers, you’d have to break the intermolecular forces, which are much weaker.
- however, polymers are long and have a large surface area, and so the accumulated intermolecular forces are quite difficult to break.
- lower melting and boiling points than giant structures, but higher points than simple structures (e.g. water)
- generally solid at room temperature
what is a property of giant covalent molecules?
- always solids at room temperature (many strong covalent bonds - high melting and boiling points)
- very strong
- don’t conduct electricity - no charged particles, even when molten. an exception is graphite
- REGULAR REPEATING LATTICES
describe silicon dioxide:
- made of silicon and oxygen atoms, in a ratio of 1:2. also known as silica, and is the main component of sand
describe diamond:
- formed from the element carbon
- each carbon atom forms 4 covalent bonds to 4 other carbon atoms - very high melting and boiling point as the covalent bonds are strong
- cannot conduct electricity (no free electrons/ions to carry electric charge)
- very hard and strong
- giant covalent structure, regular 3d pattern
describe graphite:
- formed from carbon. each carbon atom forms three covalent bonds with other carbon atoms. (forms hexagonal rings which have no covalent bonds between the layers, only weak intermolecular forces)
- high melting and boiling point (takes a great deal of energy to break covalent bonds)
- soft and slippery (hexagonal rings are arranged in layers that can easily slide over each other, which have no covalent bonds between)
- excellent conductor of electricity and heat energy (each carbon atom has a delocalised electron, which can conduct thermal energy and electricity)
describe graphene:
- a single layer of graphite (1 atom thick)
- multiple repeating hexagons. each carbon is bonded to 3 other carbons
- excellent conductor of electricity and heat (has delocalised electrons, like graphite)
- extremely strong, due to covalent bonds
- therefore useful in electronics and composites (resistant, flexible, transparent).
describe fullerenes:
- molecules of carbon atoms with hollow shapes
- usually, they have hexagonal rings of carbon atoms, but can also have rings of 5/7 carbon atoms
- sheets of graphite are bent into hollow structures
describe buckminsterfullerene:
- contains 60 carbon atoms arranged in a hollow sphere
- formula C60
- the atoms form rings, either with 5 or 6 atoms in one ring
what industries is nanotechnology being used in?
- medicine
- batteries
- food
- fashion
what are the uses of buckminsterfullerene?
- pharmaceutical delivery (strong, therefore can resist breakdown by the body, can be absorbed more easily by the body). the spheres can be formed around other molecules (e.g. drugs, helping to deliver them to certain areas of the body), acting like a cage
- used as lubricants to prevent machine parts from grinding together (weak intermolecular forces, allows molecules to easily slide past each other).
- industrial catalysts, as they have a high surface area:volume ratio
describe carbon nanotubes (a type of fullerene):
- rings formed from 6 carbon atoms, forming a hollow cylindrical shape
- high tensile strength (can be stretched without breaking)
- excellent conductor of heat and electricity (has a delocalised electron)
what is a use of carbon nanotubes?
- can reinforce materials, as they’re very long and thin (e.g. in tennis rackets). they add strength to the material without adding much weight
- nanotechnology: electrical conductor
- electronics: electrical conductor
what is a nanometre?
- 1/1000th of a micrometre (1 x 10^-9 m)
- can fit 4 atoms of a large element into 1 nanometre
describe coarse particles (pm10/dust):
- have a diameter of between 1 x 10^-5 m and 2.5 x 10^-6 m
- contains MANY MANY thousands of atoms
- often referred to as dust
describe fine particles (pm2.5):
- have a diameter between 100-2500 nanometres
- contain several thousand atoms
describe nanoparticles:
- smaller than fine particles
- have a diameter between 1-100 nanometres
- only contain a few hundred atoms
- researched by a field of science called nanoscience
- large surface area:volume ratio
what occurs when we decrease the size of a particle?
as the size of the particle decreases by ten times, the surface area : volume ratio increases by ten times.
how do nanoparticles and surface area link together?
- nanoparticles have a huge surface area : volume ratio
- this makes them useful for:
> medicines (e.g. fullerenes to deliver drugs inside our bodies, and even into our cells)
> sun creams
> cosmetics
> deodorants
> catalysts (need much less, as they have a bigger surface area for a given volume)
> electrical circuits (some can conduct electricity, e.g. to make super tiny computer chips)
what are the uses of silver nano-particles?
- antibacterial properties
- can infuse them into surgical masks/wound dressings to kill bacteria, reducing the chance of infection
why are nano-particles useful in sun creams?
- keeps sun cream from leaving a white film on the surface of the skin.
- provide better coverage
- provide more protection from the Sun’s ultraviolet rays.
what is a disadvantage of the use of nano-particles in suncreams?
- potential cell damage to the body
- what happens to them when washed into the sea? could be damaging to the environment
what are the issues of nanotechnology?
- relatively new, its effects on our bodies aren’t well understood yet. should be regulated more strictly
what is an ion?
a charged particle
- single atom, or group of atoms
- formed when atoms gain or lose electrons, in order to have a full outer shell so they’re more stable
what makes an atom more likely to react?
- losing or gaining electrons requires energy
- therefore atoms with only one atom to lose or gain are more likely to react to form ions, as it requires less energy
what is important to know about half equations?
- if the atom is becoming a positive ion and losing electrons, the electron is placed on the right of the reaction
- if the atom is gaining an electron, it’s placed on the left, to show that it’s combining with the atom
what is a molecular formula?
shows the actual number of atoms of each element present in a compound or molecule
- e.g. the molecular formula for glucose is C6H12O6 - a glucose molecule contains 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms
what is an empirical formula?
the simplest, whole number ratio of atoms of each element in a compound. doesn’t tell you exactly how many atoms there are, just the ratio of the atoms of each element
- e.g. the empirical formula for glucose is CH2O, which means that for every 1 carbon atom, there are 2 hydrogen atoms and 1 oxygen atom (1:2:1)
how would you find an empirical formula from a molecular formula, using C2H6 (ethane) as an example:
- looking at the molecular formula, the ratio of C:H atoms is 2:6
- to get the empirical formula, simplify this ratio as much as possible. divide both sides by two to get 1:3
- this means that for every 1 carbon atom, there’s three hydrogen atom
- so the empirical formula for ethane is CH3
how would you find the molecular formula from an empirical formula and an Mr?
Use this as an example:
‘an unknown compound has an empirical formula of CH3, and an Mr of 30. Find the molecular formula of the compound’
- find the Mr of the empirical formula: (1x12) + (3x1) = 15
- see how many times the Mr of the empirical formula goes into the Mr of the unknown compound: 30/15=2
- look at the empirical formula and multiply all the numbers by the multiple you just found (2). so CH3 becomes C2H6, which is your answer
how would you find the empirical formula from a mass or percentage?
use this as an example:
‘a compound is found to contain 50.05% sulfur and 49.95% oxygen by weight. what is the empirical formula for this compound?’
- assume 100g of the compound is present, which changes the percentages into grams
- sulfur: 50.05g
- oxygen: 49.95g - convert these masses to moles (moles = mass/Mr)
- moles of sulfur: 50.05/32=1.564
- moles of oxygen: 49.95/16=3.122 - divide both the mole values by the lower number of the two, to give the smallest whole number ratio between the two elements (round to nearest whole number)
- sulfur: 1.564/1.564=1
- oxygen: 3.122/1.564=1.996=2 - the ratio of sulfur:oxygen in this compound is 1:2
- use this ratio to work out the empirical formula for the compound: SO2
what substances can covalent bonds make?
- simple molecular substances. the atoms are joined by strong covalent bonds, but between the individual molecules, there are only weak intermolecular forces, which are easily broken, therefore are typically gases at room temp e.g. ammonia, chlorine, methane, water
- polymers. long chains of monomers, used to make plastic bags and tshirts
- giant covalent structures. silicon dioxide, diamond, graphite. billions/trillions of atoms arranged in a regular lattice. very strong, as the atoms are joined by covalent bonds
why do the halogens exist in different states?
- chlorine = gas, bromine = liquid, iodine = solid, giving off purple fumes
- they have different melting and boiling points
- as you go down the group, the atoms and thus the molecules get larger, meaning there’ll be more intermolecular forces, and so more energy will be required to break them
do giant covalent structures have intermolecular forces?
no weak intermolecular forces as it’s only one structure
what is an allotrope?
different structural forms of the same element in the same physical state
what is particle/kinetic theory?
- considers each particle as a small, solid, inelastic sphere
- tries to show how particles in each of the three states behave
how do particles behave in solids?
- strong forces of attraction between particles, holding them close together in a fixed position, forming a regular lattice
- definite shape and volume
- particles can vibrate in a fixed position
describe melting:
heating particles causes them to vibrate more and gain more energy. at their ‘melting point’, the particles have enough energy to break free of their bonds, and the solid melts into a liquid
how do particles behave in liquids?
- weak forces of attraction between particles, free to move around, arranged randomly. tend to stick together, fairly compact
- definite volume, even though overall shape can change (flow)
describe boiling:
heating the particles even more means they gain even more energy and move around faster, weakening the forces holding them together. when they reach the ‘boiling point’, the particles have enough energy to break the bonds altogether
how do particles behave in gases?
- the forces of attraction between the particles are very weak, so the particles are free to move around by themselves
- gases don’t have a definite shape or volume and will move to fill a container
- constantly moving particles in random motion
what happens if we heat a gas even more?
as the particles gain more energy:
- the gas will either expand
- or if the container is fixed, the pressure will increase
what happens if we cool a gas?
- the particles won’t have enough energy to overcome the forces of attraction between them, so bonds will start to form between particles, condensing the gas into a liquid
- cooling the liquid even further means the particles won’t have enough energy to overcome the attraction between them, so even more bonds will form, fixing the particles in place, and the liquid will freeze into a solid
what are the pros and cons of the particle model?
pros:
- useful simplification to help us understand a complicated concept
cons:
- particles aren’t actually, solid, inelastic or spheres in real life
- doesn’t include details about forces between particles - how strong, how many
