C1: Atomic structure and the periodic table Flashcards
define an atom
the smallest part of an element that can exist
define an ‘element’
a substance of only one type of atom
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define a compound
two or more elements combined chemically in fixed proportions which can be represented by formulae
what is a mixture? Does it have the same chemical properties as its constituent materials?
- a mixture consists of two or more elements or compounds not chemically combined together
- it does have the same chemical properties
give the 5 methods mixtures can be separated? do they involve chemical reactions?
- filtration, crystallisation, simple distillation, fractional distillation , chromatography
- they do not involve chemical reactions
describe and explain simple distillation.
- used to separate liquid from a solid
- the liquid is heated
- the vapour then rises and cools in the condenser and drips into a beaker
- solid is left in the flask and liquid is left in the beaker
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Describe and explain crystallisation
- Crystallisation is used to produce solid crystals from a solution.
- a solution is placed in an evaporating basin and heated with a Bunsen burner
- the volume of the solution decreases as some of the water has evaporated
- solid particles begin to form in the basin
- the water then evaporates leaving crystals behind
describe and explain fractional distillation
describe and explain fractional distillation
- The solution is heated to the temperature of the substance with the lowest boiling point
- This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
- All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
- the same thing occurs with the temperature of the next substance
Describe and explain filtration
- used to separate an insoluble solid suspended in a liquid
- one beaker contains a mixture of solid + liquid the other a funnel with filter paper
- this is poured into the filter funnel
- the insoluble solid gets caught in the filter paper as particles are too large
- the filtrate is the substance that comes through the filter paper
what is chromatography used for?
- used to separate a mixture of substances dissolved in a solvent.
describe and explain paper chromatography
- A pencil line is drawn on chromatography paper and spots of the sample are placed on it.
- The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent, so the samples don’t wash into the solvent container
- The solvent travels up the paper by capillary action, taking some of the coloured substances with it
- Those substances with higher solubility will travel further than the others
- This will show the different components of the ink / dye
The plum pudding model of the atom was replaced by the nuclear model.
The nuclear model was developed after the alpha particle scattering
experiment.
Compare the plum pudding model with the nuclear model of the atom
similarities :
- both have positive charges
* both have (negative) electron
differences:
- in ppm mass is spread throughout whereas in the nm mass is concentrated at the centre
- in the ppm electrons are spread throughout whereas in the NM electrons are outside the nucleus
describe the plum-pudding model and who proposed it
- the atom is a ball of positive charge with negative electrons embedded in it
- JJ Thompson
Evidence from the alpha particle scattering experiment
led to a change in the model of the atom from the plum pudding model.
Explain how.
- most (alpha) particles passed (straight) through (the gold foil)
- (so) the mass of the atom is concentrated in the nucleus
so most of the atom is empty space - some (alpha) particles were deflected / reflected
- (so) the atom has a (positively) charged nucleus
describe the Bohr/ nuclear model and how it came about
- the nuclear model suggests that electrons orbit the nucleus at specific distances (shells)
- it came about from alpha scattering experiments
what did the work of James Chadwick provide evidence for?
- the existence of neutrons in the nucleus
Chadwick’s experimental work on the atom led to a better understanding of
isotopes.
Explain how his work led to this understanding
- Chadwick provided the evidence to show the existence of neutrons
- (this was necessary because) isotopes are atoms of the same
element - but with different numbers of neutrons
describe the structure of an atom
- the atom has a small central nucleus which is made up of protons and neutrons around which there are electrons
State the masses of the
subatomic particles
Protons: 1, neutrons: 1, electrons: 0
State the relative charges
of the subatomic particles
Protons: +1, neutrons: 0, electrons: -1
what is the radius of an atom
0.1 nm or 1 x 10 ^ -10
what is the radius of a nucleus and what is it compared to that of the atom
1 x 10 ^ -14