Atomic structure and the periodic table- Chemistry Paper 1 Flashcards
What’s an element?
A substance that contains only one type of atom
What does the atomic number tell you?
The number of protons an element has
What does the mass number tell you?
The total number of protons and neutrons in an atom?
Is the atomic number the top or bottom number?
Bottom
Is the mass number the top or bottom number?
Top
What are isotopes?
Atoms of an element with the same number of protons, but a different number of neutrons. This means that they have the same atomic number but a different mass number
what is the relative atomic mass of an element?
The relative atomic mass of an element is a weighted average of the masses of the atoms of the isotopes
How do you work out the relative atomic mass?
sum of(isotope abundance X isotope mass number / sum of abundances of all isotopes
What is a compoud?
A substance that contains 2 or more elements that are chemically bonded together.
What’s a mixture?
A substance made up of 2 or more elements or compounds that aren’t chemically bonded together
What methods are used to separate out mixtures?
Physical methods, as the components of mixtures aren’t chemically joined together
What do physical methods of separation include?
- Chromatography
- Filtration
- Crystallisation
- Simple distillation
- Fractional distillation
What is chromatography used for?
Separating mixtures made up of liquids of different colours
Describe the process of paper chromatography
1) Draw a pencil line near the bottom of the sheet of chromatography paper
2) Spot the ink on the pencil line, then put the filter paper upright in a beaker of solvent.
3) Place a lid on top of the container to stop the solvent evaporating.
4) The solvent will move up the paper, carrying the ink with it
5) The different dyes will move up the paper at different rates, so the dyes will separate out and form spots in different places. Insoluble dyes will remain on the pencil line
6) The point the solvent reaches as it moves up the paper is the solvent front. When the solvent front has nearly reached the top of the paper, take the paper out of the beaker and draw a line with a pencil along the solvent front and leave to dry.
7) The end result is a pattern of spots called a chromatogram.
Why shouldn’t the ink used in chromatography touch the solvent initially?
Because this could result in the ink being washed away
Why is pencil used to draw the line at the bottom of the chromatography paper?
Because pencil is insoluble and so won’t dissolve in the solvent
What is spotting?
Placing a dot of ink on the pencil line
On some chromatograms, what does the number of spots you end up with tell you?
The number of different substances there were in the mixture
What is the Rf value in paper chromatography?
The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent
What is the mobile phase?
Where the molecules move, this can be either a liquid or a gas
What is the stationary phase?
Where the molecules can’t move. This can be a solid or a really thick liquid
Substances which travel the same distance during chromatography are…
the same
During chromatography, substances will move depending on…
how strongly the attract with the stationary phase and how strongly they react with the mobile phase.
