chemistry qma revision 2018 Flashcards
definition of an atom
smallest neutral part of an element that can take part in chemical reactions
definition of an element
made up of one type of atom, substances that cannot be split up into simpler substances
definition of a compound
different elements/different atoms that are chemically combined together (by chemical bonds)
definition of a molecule
two or more elements joined together (by covalent bonds)
definition of a mixture
two or more substances/elements/compounds that are not chemically combined. They are mixed together, they can usually be separated by physical methods
definition of a chemical change
when a reaction occurs between two or more substances to create a new chemical
definition of a physical change
a change where no new substances are formed
definition of a nucleus
the very small and dense central part of an atom
definition of an electron
a tiny particle with a negative charge
definition of a proton
a tiny positively charged particle found inside the nucleus of an atom
definition of a neutron
a dense particle found in the nucleus, it carries no charge
definition of an atomic number
the number of protons inside an atom
definition of mass number
the number of protons plus neutrons in the nucleus of an atom
definition of isotopes
atoms of the same element, which have the same number of protons (and electrons) but different number of neutrons
what do electrons orbit the nucleus in
energy levels (shells)
definition of chromatography
used to separate mixtures of coloured compounds. They are separated based on their density, - the lower the density, the further it travels up the paper
definition of magnetism
used to separate magnetic metals from non-magnetic substances
definition of crystallisation
used to separate dissolved salts from their solvent. Heating the solution evaporates the solvent leaving the salt crystals
definition of separating funnel
used to separate immiscible liquids. Opening the tap on the funnel allows the less dense bottom layer to flow through. The tap can be closed when the top layer reaches the bottom
definition of filtration
used to separate insoluble solids from liquids. The solid residue is left in the filter paper as it cannot pass through and the liquid filtrate passes through
definition of simple distillation
used to separate miscible liquids based on their different boiling points. The liquid with the lower boiling point boils first and the gas passes down the condenser, cools and condenses again.
definition of fractional distillation
used to separate miscible liquids based on their different boiling points. The liquids will evaporate and rise up the column. The liquid with the highest boiling point will condense on the beads and drip back down whilst the liquid with the lowest boiling point will rise and pass into the condenser where it will cool and condense
why have ideas about atoms changed over time
scientists have gathered new evidence from experiments and new technology has advanced
when did Democritus propose his ideas about atoms
400bc
what did Democritus say
he was the first to have the idea that everything was made of particles - he called them atoms
when did John Dalton propose his ideas about atoms
1803
what did John Dalton say
he described atoms like billiard balls and said that atoms of the same element were identical. He also thought that these atoms could not be split.
when did JJ Thompson propose his ideas about atoms
1897
what did JJ Thompson say
he discovered the electron by passing high voltage electricity through gases. He proposed the “plum pudding” model of the atom - a ball of positive charge with the negative electrons embedded in it
when did Rutherford and Marsden propose their ideas about atoms
1909
what did Rutherford and Marsden say
- conducted the gold leaf experiment by firing positive alpha particles at a thin gold foil
- expected the particles to pass straight through based on “plum pudding” model
- instead some bounced back and some deflected in other directions
- this gave rise to the “nuclear” model, a positive dense nucleus in the centre surrounded by lighter negatively charged electrons
when did Neils Bohr propose his ideas about atoms
1913
what did Neils Bohr say
agreed with the nuclear model and suggested that electrons orbited at specific distances, otherwise known as “shells”
when did Ernest Rutherford propose his ideas about atoms
1920
what did Ernest Rutherford say
suggested the name proton for a hydrogen nucleus
when did James Chadwick propose his ideas about atoms
1932
what did James Chadwick say
that there must be another particle in the nucleus. Proved the existence of the neutron and measured its mass
differences between plum-pudding and nuclear model
plum-pudding:
- single ball of positive charge with electrons in random positions
- has no nucleus
nuclear model:
- positive charge in the centre/nucleus
- electrons in fixed positions arranged in shells
- has a nucleus
comparison 1 between plum-pudding and nuclear
in plum-pudding, the protons are not sub-atomic particles (are a ball of positive charge), whereas in nuclear the protons are in the nucleus
comparison 2 between plum-pudding and nuclear
in plum-pudding, the electrons are embedded in the ball of positive charge whereas in the nuclear model they are in shells
comparison 3 between plum-pudding and nuclear
plum-pudding has no neutrons whereas the nuclear model has them in the nucleus
comparison 4 between plum-pudding and nuclear
plum-pudding has its mass spread throughout the atom whereas the nuclear model has it concentrated in the nucleus
what is the radius of an atom
0.1nm
what is ratio of a nucleus to an atom
1:10,000
how to convert nm to m
x 10^-9
how to convert m to nm
/ 10^-9
what is relative atomic mass
the average mass of the atoms of an element compared with an atom of carbon-12. The average mass takes into account the proportion of the isotopes of the element
how to calculate relative atomic mass
(total mass of all atoms of that element) / (total number of that element
4 rules of electronic structure
- always fill the shells from the centre
- the first shell can hold 2 electrons
- the second shell can hold 8 electrons
- the third shell can hold 8 electrons before the fourth starts to fill up
what is the group number equal to
number of electrons in outer shell
what is the period number equal to
number of shells
who was the first to develop the periodic table
Dobereiner
what did Dobereiner say
notice groups of elements so put forward “law of triads”. Examples: lithium, sodium, potassium & chlorine, bromine, iodine
who was the second to develop the periodic table
Newlands
What did Newlands say
- the first to order elements by atomic mass and noticed patterns of properties every 8 elements
- proposed the law of octaves
- ideas were rejected as the order went wrong after calcium
- e.g. unreactive copper in same group as lithium, sodium and potassium
who was the third to develop the periodic table
mendeleev
what did Mendeleev say
- ordered elements by atomic mass as well
- left gaps for elements that hadn’t been discovered
- swapped the order of some elements so that some properties fit the pattern
- mendeleev had no knowledge of protons electrons or neutrons but we now know he put them in atomic number
- excluded noble gases as they hadn’t been discovered
difference in boiling points between metals and non-metals
metals have high melting and boiling points whereas non-metals don’t
difference in densities between metals and non-metals
metals have a high density whereas non-metals don’t
difference in conductivity between metals and non-metals
metals are good thermal and electricity conductors whereas non-metals aren’t (except graphite)
difference in shine between metals and non-metals
metals are shiny when polished whereas non-metals are dull
difference in reactions between metals and non-metals
metals react to form negative ions and ionic compound whereas non-metals react to form molecules
difference in oxides between metals and non-metals
metals have basic oxides whereas non-metals have acidic oxides
is there a reaction between metals and non-metals?
no
difference in shape between metals and non-metals
metals are malleable (hammered in shape) whereas non-metals are brittle when solids
what group are noble gases in
0
how reactive are noble gases and why
unreactive as they have a full outer shell of electrons so they don’t want to lose or gain any
what happens to density of noble gases when you go down the group
it increases
what happens to boiling point of noble gases when you go down the group
increases as the atoms get bigger and there are more weak forces of attraction so more energy is required to break them apart
what group are alkali metals in
1
how hard are alkali metals
they are soft and can be cut with a knife
what is the melting point of alkali metals
have a low melting point, much lower than transition metals
do alkali metals conduct electricity
yes
how dense are alkali metals
some are not very dense and will float on water
what are the alkali metals’ reactions to water
lithium - fizzes and floats
sodium - fizzes floats and sometimes a yellow flame is seen
potassium - fizzes floats melts and burns with a lilac flame
metal + water –>
2Li + 2H2O –>
metal hydroxide + hydrogen
2LiOH + H^2
metal + oxygen –>
4Li + O2 –>
metal oxide
2Li2O
metal + chlorine –>
2Li + Cl2 –>
metal chloride
2LiCl
name the stages for alkali metals reactivity
- get more reactive as you go down
- have one electron in outer shell so need to lose one to have the same electronic structure as noble gas
- alkali metals further down have less attraction on outer electron, means more shielding
- outer electrons of alkali metals further down are further away from attractive force of nucleus
- the outer electron is more easily lost as there are more outer shells and they are further away from attractive force of nucleus
what group are halogens in
7
what is fluorine
a pale yellow gas
what is chlorine
a pale green gas
what is bromine
a dark brown liquid
what is iodine
a grey solid (with purple vapours)
how do halogens exist as
diatonic molecules which means they go round in pairs e.g. F2, Cl2
halogen + hydrogen –>
Cl2 + H2 –>
hydrogen halide
2HCl
halogen + metal –>
Cl2 + “Na
metal halide
2NaCl
how do displacement reactions work
a more reactive halogen displaces a less reactive halogen, a colour change can be seen
example of a word displacement reaction
chlorine + sodium bromide –> sodium chloride + bromine
example of a symbol displacement reaction
Cl2 + 2NaBr –> 2NaCl + Br2
name the stages for halogens reactivity
- halogens get less reactive as you go down the group
- have seven electrons in outer shell to have electronic structure of noble gas
- halogens further down have more shells so there is less attraction for incoming electron, means more shielding
- outer electrons of halogens further down the group are further away from attraction of nucleus
- an electron is less easily gained because there are more shells and less attraction of nucleus
- the harder it is for an atom to gain an electron, the less reactive it is
explain the reactivity of transition metals
not as reactive as alkali metals but still react with oxygen and chlorine, just more slowly
what can transition metals act as
catalysts
what type of compound do transition metals form compared to alkali metals
form coloured compounds whereas alkali metals form white compounds
what do transition and alkali metals have in common
- good conductors of heat
- good conductors of electricity
- shiny
what do transition metals react to form compared to alkali metals
ions with different charges whereas alkali metals form ions with a +1 charge
definition of collission theory
an explanation of chemical reactions in terms of reacting particles colliding with sufficient energy for a reaction to take place
definition of activation energy
the minimum energy that particles must collide with for a reaction to take place
definition of exothermic
a reaction that transfers to the surroundings
definition of endothermic
a reaction that takes in energy from the surroundings
definition of reversible reaction
a reaction in which the products can re-form the rectants
definition of hydrated
a substance that contains water in its crystals
definition of anhydrous
a substance that does not contain water
definition of equilibrium
the point in a reversible reaction where the forward and reverse reaction take place at the same rate. the amount of substances remain constant, only happens in a closed system
definition of Le Chatelier’s principle
when a change in conditions happens in equilibrium, position of equilibrium shifts to cancel out the change
equation 1 to calculate the mean rate of reaction
quantity of reactant used / time taken
equation 2 to calculate the mean rate of reaction
quantity of product formed / time taken
how can quantity of reactant or product be measured
in grams, cm^3 or moles
units for time taken in rates of reaction
g/s, cm^3/s, mol/s
how can you calculate the rate of reaction from a graph
drawing a tangent and working out the change in product divided by the change in time
what affects the rate of reaction
- concentration of reactants in solution
- pressure (when gases are reacting)
- surface area of solid reactants
- temperature
- catalyst
when will a reaction occur
when particles collide with sufficient energy
what is the minimum amount of energy particles need to react
activation energy
what will happen as the frequency of successful collisions increases
the rate of reaction will icnrease
how does increasing concentration affect rate of reaction
more particles means particles are closer together so the frequency of collisions increases so the rate of reaction increases
how does increasing pressure affect rate of reaction
more particles are closer together so the frequency of successful collisions increases so the rate of reaction increases
how does increasing the surface area of a solid reactant affect rate of reaction
more surface available for the reactant in solution to collide with so the frequency of successful collisions increases so the rate of reaction increases
how does increasing the temperature affect rate of reaction
the particles have more energy so they collide more energetically, so the frequency of successful collisions increases so the rate of reaction increases
4 properties of catalysts
- speed up the rate of reaction
- are not used up in the reaction
- different catalysts are needed for different reactions
- enzymes are biological catalysts
how do catalysts increase the rate of reaction
providing a different pathway for reaction that has a lower activation energy
why are catalysts not included in a chemical reaction
they are not used up
how is one way you can test for rates of reaction
reacting sodium thiosulfate and dilute hydrochloric acid and seeing how long it takes for the “x” to disappear with different concentrations of sodium thiosulfate
how can you make the 1st method for testing rates of reaction more accurate
using a light sensor to monitor turbidity
how is another way you can test for rates of reaction
- filling a measuring cylinder with water and inverting it into a trough with water
- placing a bung on a conical flask with acid and a magnesium ribbon with the other end underneath the measuring cylinder
- record the volume of gases at different intervals until reaction has stopped
- repeat with different concentrations of acid
what are reversible reactions
where the product can react to produce the original reactants
what will the reverse reaction in a reversible reaction be if the forward reaction is exothermic
endothermic and will take in the same amount of energy that has been released
how can the direction of a reversible reaction be changed
by changing the conditions
what happens if concentration of reactants increases in equilibrium
more products will be formed until equilibrium is reached again
what happens if concentration of products decreases in equilibrium
more reactants will react to make more products so that equilibrium is reached again
what happens if one of reactants or products change concentration in equilibrium
concentration of all substances change until equilibrium is reached
what happens in an increase in pressure in equilbrium
the equilibrium shifts to the side with smaller amounts of molecules (more reactants/products produced)
what happens in a decrease in pressure in equilibrium
the equilibrium shifts to the side with larger amounts of molecules (more reactants/prodcuts produced)
what type of reaction gets warmer and what type gets colder
exothermic gets warmer gives out heat
endothermic gets colder takes in heat
how can you tell if a reaction is exothermic (gets warmer)
the ΔH values are negative
what happens in an increase in temperature in equilbrium
the equilibrium shifts to the endothermic side
what happens in a decrease in temperature in equilbrium
the equilibrium shifts to the exothermic side
