Atomic structure and the periodic table Flashcards
(60 cards)
What is an element?
An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.
What are the 7 diatomic elements
H2, N2, O2, F2, Cl2, Br2 and I2.
Define a compound
A compound is a pure substance made up of two or more elements chemically combined and which cannot be separated by physical means
Name 7 covalent compounds
H2SO4 is sulfuric acid
NH3 is ammonia
CH4 is methane
HCl is hydrochloric acid (or hydrogen chloride if it is a gas)
C6H12O6 is glucose
C2H5OH is ethanol
HNO3 is nitric acid
Law of Conservation of Mass
The total mass of reactants is always equal to the total mass of products
What are ions which are present but do not take part in reactions called?
Ions which are present but do not take part in reactions are called spectator ions
Do mixtures change chemical properties?
Can they be separated by physical or physical processes?
Each constituent of the mixture retains its chemical properties
The parts of a mixture are not chemically bonded together and so they can be separated by physical means
When is filtration used?
Filtration is used to separate an insoluble solid from a liquid
Describe the steps of filtration (4 steps)
-A piece of filter paper is placed in a filter funnel above a beaker
-A mixture of insoluble solid and liquid is poured into the filter funnel
-The filter paper will only allow small liquid particles to pass through as filtrate
-Solid particles are too large to pass through the filter paper so will stay behind as a residue
When is crystallisation used?
Crystallisation is used to separate a soluble solid from a liquid
Describe the steps of crystallisation (4 steps)
-Solution is heated to allow the solvent to evaporate
-To test if the solution is saturated a clean, dry, cold glass rod is dipped into the solution
If the solution is saturated, crystals will form on the glass rod
-The saturated solution is then allowed to cool slowly
Crystals begin to grow as solids come out of solution due to decreasing solubility
-The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
When can simple distillation be used instead of fractional distillation?
Simple distillation is used to separate mixtures which are having boiling points with a gap of a minimum of 50 degrees.
When can simple distillation be used?
-This is used to separate a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids
4 steps for simple distillation
-The solution is heated and a liquid evaporates producing a vapour which rises through the neck of the round-bottomed flask (e.g. for saltwater, this would be water boiling at 100 oC)
-The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
-After all the liquid is evaporated from the solution, only the solid solute will be left behind
When is fractional distillation used?
This is used to separate two or more liquids that are miscible with one another
Give the 4 steps of fractional distillation
-solution is heated to the temperature of the substance withe lowest BP
-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
When is paper chromatography used?
This technique is used to separate substances that have different solubilities in a given solvent
Give the 4 steps of fractional distillation
-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
-Different substances have different solubilities so will travel at different rates, causing the substances to spread apart
Those substances with higher solubility will travel further than the others
List the order of the scientific discoveries related to the atom (5 key people)
Dalton-‘billiard ball mode’ indivisible
Thomson-‘plum pudding model’ electron
Rutherford-‘nuclear atom’ empty space and electrons orbiting nucleus in fixed paths
Bohr-‘planetary model’-electrons orbit the nucleus in orbitals (set distances) from nucleus
james chadwick-proposed the neutron
2 pros and 2 cons of Daltons model
pros: roughly spherical, limited amount of elemnets
cons: don’t tell us about electrical nature of atoms, continuous atoms
2 pros and cons of thomsons model
pros: accounts for electrical nature of an atom, discontinuous atom
cons: Low density of alpha particle can’t explain the bouncing back of alpha particles in gold foil experiment
2 pros and cons of rutherfords model
pros: Dense nucleus explains the bouncing back of alpha particles in the gold foil scattering experiment
cons: failed to explain stability of elctrons in circular path
radius of an atom
0.1nm
How many times smaller than the radius of the atom is the radius of the nucleus?
10,000
