Section 14: Groups In Periodic Table Flashcards
what are group 1 metals also known as
‘alkali metals’
what are the alkali metals
- lithium
- sodium
- potassium
- rubidium
- caesium
- francium
chemical properties of alkali metals
they all have 1 electron in the outershell.
physical properties of alkali metals
- low melting points
- low boiling points
- very soft, they can be cut with a knife
what do alkali metals form and what does this cause
alkali metals form ionic compounds. they lose their single outer electron so easily so they dont form covalent bonds
are group 1 elements reactive or unreactive and why
they are very reactive. this is because they readily lose their single outer electron to form a 1+ ion with a stable electronic structure.
what makes an element reactive
the more readily a metal loses its outer electron, the more reactive it is. making group 1 metals very reactive
what happens as you go down group 1
as you go down group 1, the alkali metals get more reactive. the outer electrons are more easily lost as it is further away from the nucleus so it is less strongly attracted to the nucleus and less energy is needed to remove it.
what happens when group 1 metals react with cold water
reactions with cold water produces hydroxide and hydrogen gas
what happens when alkali metals are put in water
they act vigorously. the reaction produces hydrogen gas and a hydroxide of the metal
what is the word equation of the reaction between sodium and water
sodium+water=sodium hydroxide + hydrogen
what is produced when cold water is reacted with group 1 elements
hydroxide and hydrogen gas
how does lithium react with water
moves around the surface and fizzing furiously
how does sodium react with water
moves around more than lithium but less than potassium, fizzes more and also melts in the heat of the reaction
how does sodium react with water
moves around more than lithium and sodium, fizzes more and also melts in the heat of the reaction
what are the elements of group 7s
- fluorine
- chlorine
- bromine
- iodine
- astatine
what are group 7s also known as
halogens
what do group 7s all have in common
all group 7 elements have 7 electrons in their outer shell so they all have similar chemical reactions
how do halogens exist and what does it mean
in diatomic molecules.
sharing one pair of electrons in a covalent bond giving both atoms a full outershell
what are the diatomic molecules
F 2, Cl 2, Br 2 and I 2
what happens as you go down group 7
as you go down group 7, the melting and boiling point increases
what happens to chlorine at room temperature
chlorine- a fairly reactive, poisonous green gas
what happens to bromine at room temperature
bromine- poisonous, red brown liquid which gives off an orange vapour
what happens to iodine at room temperature
iodine- a dark grey crystalline solid which gives off a purple vapour
how do you predict trends in the group 7 elements
the melting point increases down the group and the colour of the halogen gets darker
test for chlorine
holding a piece of blue litmus paper over chlorine gas. chlorine will bleach the litmus paper turning it white. it may turn red for a moment, this is because the solution of chlorine is acidic
why does the reactivity series go down in group 7
- a halogen atom only needs to gain one electron to form a 1- ion with a stable electronic structure
- the easier it is for a halogen atom to attract an electron, the more reactive the halogen will be
- as you go down group 7, the less reactive- this is because it gets harder to attract the extra electron to fill the outershell when it becomes further away from the nucleus as the atomic radius is larger
what can halogens react with
metals and hydrogen
how do halogens form metal halides
metal halides are salts. the halogen will react vigorously with some metal to form metal halides
equation for halogens reacting with metals and hydrogen
2Na+ Cl2 —-> 2Nacl
chlorine- halogen
how are hydrogen halides formed
halogens can also react with hydrogen to form hydrogen halides
equation for hydrogen halides
H2 + Cl2 —-> 2HCl
why can hydrogen halides form acidic solutions
hydrogen halides are soluble so they can dissolve in water forming acidic solutions
what is displacement
a more reactive halogen will displace a less reactive one. a more reactive element will ‘push out’ -displace- a less reactive element from a compound
what is reduction
when the halogen GAINS electron
what is oxidation
when a halide LOSES electrons
do halides use oxidation or reduction
oxidation
do halogens use oxidation or reduction
reduction
group 0 elements
also known as noble gases
- helium
- neon
- argon
- krypton
- xenon
- radon
physical features of noble gases
they are colourless gases at room temperature
chemical features of noble gases
-they are all monatomic where their gases are made up of single atoms
- they are more or less inert, they dont react with much at all
why dont noble gases react
they have a full outershell of electrons meaning they dont give or gain electrons easiy
why are noble gases non flammable
as they are inert
uses for noble gases
1- argon- provides an inert atmosphere in filament lamps. since its non-flammable it stops very hot filament from burning away - like flash photography
2- argon and helium can also be used to protect metals that are being welded. the inert atmosphere stops the hot metal reacting with oxygen
3- helium is used in airships and balloons. this is because helium has a lower density than air so it makes balloons float. is is also non-flammable which makes it safer to use than hydrogen gas
properties of noble gases
- boiling point, melting point and density increases as you go down
collision theory
particles must collide with enough energy in order to react
what does the rate of reaction depend on
- collision frequency
- the energy transferred during a collision
- the more collisions the higher the rate of reaction
collision frequency
the more successful collisions there are, the faster the reaction is
the energy transferred during a collision
the minimum energy that particles need to react when they collide is called activation energy. particles need to collide with atleast the activation energy for the collision to be successful
the more collisions the higher the rate of reaction
reactions happen if the particles happen with enough energy to react.
so if you increase the number of collisions or energy with which the particles collide, the reaction happens more quickly
factors that lead to an increase in the rate of reaction
- increasing the temperature
- increasing the concentration or pressure
- smaller solid particles or more surface area means a higher rate
increasing the temperature
when the temperature increases, the particles move faster. this means there will be more collisions as they are moving faster
higher temperatures also increase the energy of the collisions as the particles are moving faster. reactions only happen if the particles collide with enough energy
increasing the concentration or pressure
concentration: if a solution is more concentrated, it means there are more particles of reactant in the same volume. this makes collisions more likely.
pressure: in a gas increasing the pressure means that the particles are more crowded. this means that the frequency of collisions between particles will increase. so the rate of reaction will also increase
smaller solid particles or more surface area means a higher rate
if one reactant is a solid, breaking it into smaller pieces will increase its surface area:volume ratio.
more solid will be exposed compared to its overall volume.
the particles around it will have more area to work on, so they frequency of collisions will increase.
what is a catalyst
increases the rate of reaction without it being chemically changed or used up in the reaction.
advantages of catalysts
- increases the rate of reaction without it being used up
- because it isnt being used up, it wont change the products of the reaction.
- this also means that you only need abit to catalyse large amounts of reactants
how do catalysts work
- catalysts work by decreasing the activation energy.
- they do this by providing an alternative pathway that has a lower activation energy
- as a result, more of the particles have atleast the minimum amount of energu needed for the reaction to occur when the particles collide.
enzymes
enzymes control cell reactions. enzymes are biological catalysts
what are biological catalysts
they catalyse the chemical reactions in living cells
reactions catalysed by enzymes
- respiration
- photosynthesis
- protein synthesis
fermentation
- enzymes from yeast cells are used in the fermentation process which is used to make alcoholic drinks
- they catalyse the reaction that converts sugars into ethanol and carbon dioxide
exothermic reaction
gives out energy to the surroundings. usually in the form of heat. it is shown by a rise of temperature of the surroundings.
endothermic reaction
takes in energy from the surroundings. usually in the form of heat. it is shown by a decrease in temperature of the surroundings
what is activation energy
the minimum amount of energy needed for the particles to collide and for bonds to break in order for a reaction to start.
how to measure energy change
- put a polystyrene cup into a large beaker of cotton cool.
- add a known volume of your first reagent to the cup
- measure the initial temperature of the solution
- add a measured mass/volume of your second reagent and stir the reaction mixture
- put a lid on the cup to reduce any energy lost by evaporation
- record the maximum or minimum temperature that the mixture reaches during the reaction.
- calculate the temperature change
what does the cotton wool do
gives insulation to help limit energy transfer to or from the reaction mixture
how do u measure the temperature change when dissolving salts in water
- adding the salt to a polystyrene cup of water and measuring the change in temperature when the salt has dissolved
- dissolving ammonium chloride decreases the temperature of the reaction mixture - endothermic
- dissolving calcium chloride causes the temperature of the solution to rise- exothermic
is type of reaction occurs when dissolving ammonium chloride decreases the temperature of the reaction mixture
endothermic
is type of reaction occurs dissolving calcium chloride causes the temperature of the solution to rise
exothermic
neutralisation reactions
- an acid and a base reacts to form a salt and water
- most neutralisations are exothermic
- neutralisation reaction between ethanoic acid sodium carbonate endothermic
displacement reactions
- a more reactive element displaces a less reactive element in a compound. these are exothermic as they release energy
- zinc powder and copper sulfate react in a displacement reaction forming zinc sulfate and copper.
precipiation reaction
- precipitates are insoluble solids which can form when two solutions are mixed together.
- precipitation reactions are exothermic
bond energies
energy must always be supplied to break bonds.
what happens during a chemical reaction
old bonds are broken and new bonds are formed.
- energy must be supplied to break existing bonds so bond breaking is an endothermic process
- energy is released when new bonds are formed so bond formation is an exothermic process
