Atomic Structure Flashcards
Approx. How many elements are in the periodic table
100
What is a compound
2 or more elements that are chemically combined
What is an element
A substance with only one type of atom
Do compounds share the same properties as the elements they’re made up of?
No
What is a mixture ?
Two or more elements athat are not chemically combined
Do mixtures share the same properties as the elements they’re made up of?
Yes
What are the methods through
which mixtures can be separated (5) and do these involve
chemical reactions?
Filtration
Crystallisation
Simple distillation
Fractional distillation
Chromatography
They do not involve chemical reactions
Describe and explain simple distillation.
Simple distillation is used to separate liquid from a solution – the liquid boils off and condenses in the condenser.
The thermometer will read the boiling point of the pure liquid.
Contrary to evaporation, we get to keep the liquid.
Describe and explain crystallisation/evaporation
Evaporation is a technique for separation of a solid from a solvent (e.g. salt from H2O).
The solution is heated until all the solvent evaporates; the solids stays in the vessel.
Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved).
Then, we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures.
The crystals can be collected and separated from the solvent via filtration.
Describe and explain fractional distillation
Fractional distillation is a technique for separation of a mixture of liquids.
It works when liquids have different boiling points.
The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask.
The fractionating column contains glass beads. It helps to separate the compounds.
In industry, mixtures are repeatedly condensed and vapourised. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of the
column.
Describe and explain filtration
Filtration is used to separate an insoluble solid is suspended in a liquid.
The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper.
The filtrate is the substance that comes through the filter paper.
Apparatus: filter paper + funnel
Describe and explain chromatography
Chromatography is used to separate a mixture of substances dissolved in a solvent.
In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent.
The bottom of the paper has to be in contact with the solvent.
The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).
Give the orders of the different versions of the atom model (5)
John Dalton - all matter was made of atoms
JJ Thompson - plum pudding model
Ernest Rutherford - nuclear model I
Neils Bohr - planetary model
James Chadwick - discovery of neutrons
Describe the plum-pudding model,
And who created it?
The atom is a ball of positive charge with negative electron embedded in
it.
Describe Bohr’s planetary model and how it came about
The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) – it came about from the alpha scattering experiments
What did the work of James Chadwick provide evidence for?
The existence of neutrons in the nucleus
State the relative masses and relative charges of the proton, neutron and electron
Masses: 1, 1, very small
Charges: 1, 0 , -1
