topic one: Atomic Structure and the Periodic Table Flashcards
what is the charge of a proton, neutron and electron?
proton - positive, +1
neutron- neutral, 0
electron- negative, -1
what is the relative mass of a proton, neutron and electron?
proton- 1
neutron- 1
electron- 1/2000
what is the overall charge of an atom?
neutral, or 0
why do atoms have a neutral charge?
they have the same number of positive protons and negative electrons, so the charges cancel out.
what does the atomic number of an atom tell you?
the number of protons.
what does the mass number of an atom tell you?
the total number of protons and neutrons.
how can you use the atomic number and mass number of a given atom, to work out how many neutrons it has?
number of neutrons = mass number - atomic number.
what is an element?
substance made up of only one type of atom, so where all the atoms of a substance have the same number of protons.
approximately how many different elements are there?
100.
what is an isotope?
different forms of the same element, which have the same number of protons but a different number of neutrons.
what does relative atomic mass mean?
average mass of all the isotopes of an element, taking into account the abundance and mass number of each isotope.
what is the formula for relative atomic mass?
sum of: (isotope abundance x isotope mass number)/ sum of abundances of all isotopes.
what is a compound?
substance formed from two or more elements, where the atoms of each are in fixed proportions, and are held together by chemical bonds.
what is a mixture?
group of different elements or compounds which are not chemically bonded.
what is a molecule?
substance that contains two or more atoms held together by chemical bonds.
what is a reactant?
the starting materials in a chemical reaction.
what is a product?
new substances produced by a chemical reaction.
which are the 6 methods through which mixtures can be separated?
1.filtration
2.chromatography
3.crystallisation
4.evaporation
5.simple distillation
6.fractional distillation
what is filtration used for?
used to separate insoluble solids from liquids.
describe the technique for filtration.
- place a piece of filter paper in a funnel, and put the funnel over a beaker.
- pour your mixture through the funnel.
- any insoluble solids will be caught by the filter paper, we call this the residue.
4, any liquid or dissolved substances will pass straight through, we call this the filtrate.
what is evaporation used for?
to separate a dissolved solid from a liquid.
describe the technique for evaporation.
heat your solution until all of the solvent evaporates, and only solids remain. (normally done by placing the solution in an evaporating dish on a tripod, and heating with a Bunsen burner
describe the technique for crystallisation.
- pour the solution into an evaporating dish.
- heat it with a Bunsen burner.
- stop heating when crystals start to form and allow to cool down.
- either allow the rest of the water to evaporate, or filter out the crystals in an oven.
- dry crystals.
what is the benefit of using crystallisation rather than evaporation as a separating technique?
the excess heat used in evaporation can sometimes cause the crystals to break down by thermal decomposition.
how would you isolate the sand and salt from a mixture of salt and sand?
- place mixture in water and stir. the salt will dissolve but the sand wont.
- pour mixture through filter paper and funnel. The sand will get stuck on the filter paper.
- evaporate water by heating. this will leave behind the salt.
what is chromatography used for?
separates the components of a mixture based on their solubility.
what is a ‘pure’ substance?
a substance that only contains one type of element or compound.
what is a solution?
a mixture that contains a solute (solid) dissolved in a solvent (liquid).
what do soluble and insoluble mean?
soluble - a substance that can dissolve in liquid
insoluble - cannot dissolve in liquid.
what is the purpose of simple distillation?
used to separate a liquid from a mixture, but when we want to keep the liquid.
describe the process of simple distillation.
- place solution in a flask and heated so that the liquid evaporates into vapour.
- the vapour will pass into a condenser where it condenses back into a liquid.
- the liquid is collected into a beaker.
why can you not use simple distillation for mixtures that contain multiple different liquids?
if the different liquids have similar boiling points, those liquids may evaporate at the same time.
when would you need to use fractional distillation rather than simple distillation?
when the mixture contains multiple liquids with similar boiling points.
how does fractional distillation work?
1, solution is placed into a flask and is gently heated.
2. the liquid with the lowest boiling point evaporates into a vapour and passes through the fractionating column.
3. as it passes into the condenser it condenses back into a liquid, and is collected in a beaker.
4. if another liquid has evaporated, it would have condensed again while passing through the Fractionating column.
5. as the temperature is increased, the process repeats for the liquid with the second lowest boiling point, which is collected in a different beaker and so on.