end of y10 full summary Flashcards
what is an atom
The smallest part of an element that can exist
what is a molecule
a particle that consists of two or more atoms chemically bonded together
how are cations and anions formed?
They are created when an atom or molecule gains or loses electrons. Gaining electrons creates a negatively charged ion; losing electrons creates a positively charged ion.
what are ionic bonds?
the electrostatic attraction between oppositely charged ions.
why do compounds with giant ionic lattices have high melting and boiling points?
Since a giant ionic lattice contains a large number of ions and hence a large number of ionic bonds, it takes a lot of energy to break these strong electrostatic forces of attraction between the oppositely charged ions. As a result, an ionic compound will have a high melting or boiling point.
so ionic compounds conduct electricity? why/why not?
they do not conduct electricity when solid
- their ions are held in fixed positions and cannot move
they conduct electricity when molten and in aqueous solution
- ions are free to move
what is a covalent bond?
the electrostatic attraction between two nuclei and a shared pair of electrons
why are substances with a simple molecular structure gases or liquids, or solids with low melting and boiling points?
Very little energy is needed to overcome the intermolecular forces, so simple molecular substances usually have low melting and boiling points.
what are the trends in melting and boiling points of substances with simple molecular structures and why?
generally, when their relative mass increases, so do the melting and boiling points. When molecules increase in size, the strength of the intermolecular forces also increases. More energy is required to overcome the relatively stronger intermolecular forces and therefore larger molecules have higher melting and boiling points.
why are substances with giant covalent structures solids with high melting and boiling points?
They have very high melting and boiling points – this is because a lot of strong covalent bonds must be broken.
do covalent bonds conduct electricity? why/why not?
they do not conduct electricity
- the molecules are neutral and there are no charged particles (no ions or electrons) to move and carry charge.
what is metallic bonding?
A metallic bond is the strong electrostatic attraction between sea of negative delocalised electrons and positive metal ions.
what are the typical physical properties of metals?
- malleable
- conduct electricity because their delocalised electrons carry electrical charge through the metal
what is an alloy?
an alloy is a mixture of a metal and one or more elements, usually other metals or carbon
why are alloys harder than pure metals?
They are made up of atoms of different sizes, rather than being uniform. This means that the layers of atoms cannot slide over each other easily, making the whole alloy much stronger than any of the pure metals that the alloy contains in isolation.
what is a hydrocarbon?
A hydrocarbon is a compound that is made out of only hydrogen atoms and carbon atoms.
what is crude oil
crude oil is a mixture of hydrocarbons
whats a functional group
A functional group is defined as a particular group of atoms which are responsible for how the molecule reacts
what is an alkane
The alkanes are a homologous series of hydrocarbons. A compound that contains hydrogen and carbon only.. This means that they have similar chemical properties to each other and they have trends in physical properties. For example, as the chain length increases, their boiling point increases.
whats a homologous series
Homologous series are families or groups of organic compounds that have similar features and chemical properties due to them having the same functional group.
what is an alkene?
Alkenes are a homologous series of hydrocarbons that contain a carbon-carbon double bond
how do you name alkanes
number of carbons:
1- meth
2 - eth
3 - prop
4 - but
5 - pent
6 - hex
number the carbons to give the branch the smallest number possible
the branch is named by taking the code (from above) and adding -yl.
example:
2 - methyl propane
how do you name alkenes
5 - methyl - 2 - hexene
5-methyl:
methyl - branch length
5 - location of branch
2-hexene:
hexene - longest chain length
2 - location of double bond
double bond takes priority when minimising number (eg. 5-methyl-2-hexene instead of 2-methyl-5-hexene)
what is the general formula for alkanes
C(n)H(2n+2)
what does it mean if a hydrocarbon is saturated?
hydrocarbons with only single bonds
what is the general formula for alkenes
C(n)H(2n)
what is isomerism
Isomerism is the phenomenon in which more than one compounds have the same chemical formula but different chemical structures.
how can bromine be used to distinguish between an alkane and an alkene?
bromine water will go colourless when mixed with an alkene
what is the difference with melting and boiling points between a pure substance and a mixture
a pure substance has a fixed melting and boiling point
a mixture may melt or boil over a range of temperatures
what is the industrial process used to separate crude oil into fractions and how?
it is called fractional distillation
During the fractional distillation of crude oil:
heated crude oil enters a tall
fractionating column
, which is hot at the bottom and gets cooler towards the top
vapours
from the oil rise through the column
vapours
condense
when they become cool enough
liquids are led out of the column at different heights
Small hydrocarbon molecules have weak
intermolecular forces
, so they have low boiling points. They do not condense, but leave the column as gases. Long hydrocarbon molecules have stronger intermolecular forces, so they have high boiling points.
what are the names and uses of the main fractions obtained from crude oil?
refinery gases - bottled gas (30 degrees, black/dark brown)
gasoline - fuel for car engines (100-150 degrees, transparent yellowish)
kerosene - fuel for aircraft and stoves (200-300 degrees, pale, yellow or colourless)
diesel - fuel for road vehicles and trains (200-300 degrees)
fuel oil - fuel for ships, heating and power stations (350-450 degrees, dark brown)
bitumen - road surface and roofing (above 500, black)
gets darker as boiling point increases. viscosity increases as well.
what is a fuel
a substance that, when burned, releases energy
what is complete and incomplete combustion
In complete combustion, there is a sufficient supply of oxygen which is able to react with the burning hydrocarbon allowing the reaction products H2O and CO2 to be formed. In incomplete combustion there is a lack of oxygen so when heat is applied carbon monoxide is released.
possible products of incomplete:
- carbon monoxide
- carbon particles
- water
possible products of complete:
- water vapour
- carbon dioxide
why is carbon monoxide poisonous?
Carbon monoxide is a poisonous gas which binds to haemoglobin. in your red blood cells, preventing them from carrying oxygen to the cells in your body.
what happens in car engines to nitrogen and oxygen?
nitrogen and oxygen in the air react, forming oxides of nitrogen due to the high temperature reached
what can happen in the combustion of some impurities in hydrocarbon fuels
the formation of sulfur dioxide of nitrogen oxide. these contribute to acid rain
what is cracking
long-chain alkanes are converted to alkenes and shorter-chain alkanes by catalytic cracking (using silica or alumina as the catalyst and a temperature in the range of 600-700 degrees)
why is cracking necessary
helps deal with the balance between supple and demand for different fractions
what happens when alkenes react with bromine
they produce dibromoalkanes. For example, ethene reacts with bromine to produce dibromoethane. The double bond between the two carbon atoms breaks and the bond between the bromine atoms in the bromine molecule breaks.
how is an addition polymer formed?
it is formed by joining up many small molecules called monomers
what are some problems in the disposal of addition polymers?
they have an inertness and inability to biodegrade so end up in landfill or in the sea, damaging wildlife and taking up valuable land
the production of toxic gases when they are burned can cause health risks to wildlife and humans
what is a mono-substitution reaction with alkanes
if an alkane reacts with a halogen (eg. chlorine, bromine) in the presence of ultraviolet radiation, one of the hydrogens is replaced by one of the halogens.
example:
CH4 + Cl2 –> CH3Cl + HCl
how does the electron configuration relate to an element’s position on the periodic table?
the number of electrons in the outermost shell of an element is represented in the periodic table as the group number that element is situated in
why do elements in the same group demonstrate similar chemical properties?
The physical and chemical properties of elements depend on the number of valence electrons. Elements present in the same group have the same number of valence electrons.
how does lithium react with water
When lithium is added to water, lithium floats. It fizzes steadily and becomes smaller, until it eventually disappears.
how does sodium react with water
When sodium is added to water, the sodium melts to form a ball that moves around on the surface. It fizzes rapidly before it disappears.
how does potassium react with water
When potassium is added to water, the metal melts and floats. It moves around very quickly on the surface of the water. The metal self-ignites, which also ignites the hydrogen gas.
what is the trend in terms of electronic configurations in Group 1
the outer electron gets further from the nucleus. the attraction between the nucleus and outer electron gets weaker
how can we predict the properties of alkali metals using trends of Group 1?
As the number of electron shells increases down group 1, the outer electron becomes easier to lose, and the reactivity of the elements increases.
what are the colours, physical states and trends in physical properties of the halogens?
fluorine - gas, yellow
chlorine - gas, green
bromine - liquid, red-brown liquid, orange/brown vapour
iodine - solid, grey solid, purple vapour
melting and boiling points increase down the group. as the relative molecular mass increases, the intermolecular forces of attraction become stronger and therefore more energy must be put in to overcome these stronger forces of attraction.
how can we use trends in Group 7 to predict the properties of other halogens?
In group 7, the further down the group an element is, the higher its melting point. and boiling point close boiling pointThe temperature at which a substance rapidly changes from a liquid to a gas.. This is because, going down group 7: the molecules become larger.
As you go down group 7, reactivity of the halogens decreases because: The atomic mass of the halogens increases. They increase in electron shells; so the atoms are larger as you go down the group. Therefore, the attraction of the outer electron to the nucleus decreases as you go down group 7.
what do the terms oxidation, reduction, redox, oxidising agent and reducing agent mean?
oxidation - Oxidation is the loss of electrons from a substance. It is also the gain of oxygen by a substance.
reduction - Reduction is gain of electrons, loss of oxygen
oxidising agent - cause oxidation reactions to take place, gains electrons from other atoms or ions (is itself reduced)
reducing agent - cause reduction reactions to take place, loses electrons to other atoms or ions (is itself oxidised)
redox - A redox reaction is one in which both oxidation and reduction take place.
what is a mole?
a unit for an amount of substance
