unit 3.1 mr allen Flashcards
periodicity definition?
The repeating pattern of properties of elements across different periods of the periodic table. (Trends= physical and chemical properties)
periodicity of several properties includes:
- electron configuration
- ionisation energy
- structure
- melting point
first ionisation energy definition…
the energy required to remove one mole of electrons from one mole of atoms in a gaseous state
1st ionisation of sodium?
Na(g)–>Na^+(g) + e^-
1st ionisation of magnesium?
Mg(g)–>Mg^+(g) + e^-
the stronger the pull in ionisation energy, the…
more energy needed to pull out the electron
talk about the trend of ionisation energy upon the periodic table
ionisation energy decreases as you go down a group and increases as you move along a period.
energy per mol symbol
triangleH
what element has the highest ionisation energy in group 1
lithium
why does ionisation energy decrease as you go down a group? (lengthy)
- down the group, there is a higher nuclear charge (more protons present in nucleus of atom)
- however, the distance between the outer electron and the nucleus increases, so its further away from the nuclear attraction of the protons in the nucleus.
- there is also increased shielding due to more electron shells between outer electron and nucleus.
- the overall effective nuclear attraction is thus less and less energy is required to move outer most electrons.
- overall, this weakens the effect of nuclear charge so less energy is required to remove outer most electrons.
why does ionisation energy decrease as you go down a group? (simplified)
- atomic radius increases
- more inner shells so shielding increases
- nuclear attraction on outer electrons decrease (first ionisation thus decreases)
1st ionisation across period 3:Na having a lower ionisation that magnesium, why
because magnesium has…
- increased nuclear charge (extra proton)
- electron added to the same shell- same distance and shielding
- atomic radii decreases, less distance from nucleus
- more effective nuclear attraction and harder to remove electron (takes more energy)
1st ionisation across period 3 EXCEPTION: magnesium having a higher ionisation energy than aluminium
because aluminium has…
- outer most electron in P orbital rather than S orbital, which has a higher energy level
- shielding from S orbital
- even though there are more protons in Al, the overall effective nuclear attraction is less (more shielding)
1st ionisation across period 3 EXCEPTION: P having a higher ionisation energy than S
because. ..
- the 3 electrons in P are in separate P-orbitals
- 2 of the 4 electrons in S are in the same P-orbital.
- there is spin pair repulsion (repulsion between paired electrons) here ^
- this outweighs the effect of having an extra proton in the nucleus
across a period, what happens to the atomic radii
it gets smaller
why does the atomic radius get smaller as you go across the period
- you add a proton to the nucleus each time
- the electrons being added are being added to the same energy level so have the same shielding
- thus electrons are more tightly held and are physically closer to the nucleus.
what does 2nd ionisation energy mean
the energy needed to remove 1 mole of electrons from 1 mole of 1+ ions in a gaseous state
2nd ionisation of Ne
Ne^+(g)–>Ne^2+(g)+e^-
3rd ionisation of Na
Na^2+(g)–>Na^3+(g)+e^-
what happens to the energy of successive ionisation energies?
the energy would increase because each ion becomes more positive so it takes more energy to overcome that
why are successive ionisation energies always greater than the previous one
- the electron is being pulled away from a more positive species
- less repulsion between remaining electrons and each shell will be drawn in slightly closer to the nucleus.The ion increases the attraction on the remaining electrons and so the energy required to remove the next electron is larger.
- large increases occur when there is a change of shell, this can be used to predict a group of an unknown element
- large increase when electron being removed is from a shell closer to the nucleus
what are the 3 factors affecting ionisation energy
- atomic radius
- nuclear charge
- electron shielding
does first ionisation energy increase or decrease between the end of one period and the start of the next? why?
DECREASE
- there is an increase in atomic radius
- there is an increase in electron shielding
does atomic radius increase or decrease down a group
increase
4 properties of giant metallic lattices
- malleable
- ductility
- good electrical conductors
- high bp and mp
what is a ductile metal?
a metal that can be stretched
eg- made into wires
what is a malleable metal?
a metal that can be shaped into different forms
describe the structure, forces and bonding in every element across period 2
Li&Be- giant metallic, strong attraction between positive ions and delocalised electrons- metallic bonding
B&C- giant covalent, strong forces between atoms - covalent bonding
N2,O2,F2,Ne- simple molecular, weak intermolecular forces between molecules: covalent bonding within molecules & intermolecular forces between molecules
describe the structure, forces and bonding in every element across period 3
Na,Mg,Al- giant metallic, strong attraction between positive ions and delocalised electrons- metallic bonding
Si- giant covalent, strong forces between atoms - covalent bonding
P4,S8,Cl2,Ar- simple molecular, weak intermolecular forces between molecules: covalent bonding within molecules & intermolecular forces between molecules
group 2 metal plus oxygen=
form a metal oxide
metal plus water=
metal hydroxide plus hydrogen gas
group 2 metal plus acid=
salt+ hydrogen gas
what happens to ionisation energy as you go down group 2
ionisation energy decreases
why does ionisation energy decrease as you go down group 2 and why does reactivity increase down a group
- in order for group 2 metals to react, they need to loose 2 electrons
- this happens more easily down the group as electrons are further away from the positive nucleus
- even though there are more protons, effective nuclear charge is less and electrons are more easily lost
- thus reactivity increases
what happens to the solubilities of group 2 hydroxides as you go down the group ( along with solubility, what also is affected and dos it increase or decrease)
- solubility increases
Mg(OH)2=insoluble
Ba(OH)2=very soluble
pH increases and alkalinity increases
why is Ba(OH)2 more soluble than Mg(OH)2
Ba and OH are able to move apart easier- more OH- ions are released (more alkaline due to more splitting)
what is a reducing agent
something that is able to cause something to be reduced and itself oxidised.
all group 2 metal oxides react with water and acids apart form the oxide…
…berilium oxide
metal oxide+ water=
metal hydroxide
metal oxide+ acid=
salt plus water
what do all group 2 sulphates look like
all are white solids
talk about the solubility of barium sulphate and what it can be used for
insoluble in water and can be used as a test for a sulphate (forms white precipitate)
talk about group two metal carbonates solubility in water@@@
insoluble in water
what happens when a group 2 metal carbonate is heated
it decomposes on heating
metal carbonate plus heat general formula
MCO3(s)==(heat)==MO(s)+CO2(g)
is it easier to decompose group 2 metal carbonates at the top of the group or the bottom.
the ease at which the carbonates decompose decreases down the group
what does barium carbonate require to decompose
strong heating
is decomposition of group 2 metal carbonates a redox reaction?
no- oxidation number of all elements stay the same
what are the two uses of group 2 metal hydroxides (include equations)
calcium hydroxide: added to neutralise soil (H+ ions are neutralised)
Ca(OH)2(s)+ 2H+(aq) ==> Ca^2+(aq) + 2H20
magnesium hydroxide:
used as an antacid for indigestion tablets
Mg(OH)2(s) + 2H+(aq) ==> mg^2+(aq)+2H20(l)
what are magnesium hydroxide and calcium hydroxide regarded as??
weak alkalis
what two things increase down group 7
- atomic radius
- melting point and boiling point
what 3 things decrease down group 7
- reactivity
- electronegativity
- ionisation energy
description of: F2 Cl2 Br2 I2
F2= pale yellow gas
Cl2= green gas
Br2=brown liquid that forms a brown gas
I2= black shiny solid that forms a purple gas when it sublimes
halogens and water: chorine plus water
Cl2(g)+H20(l) <==> HCl (aq) + HClO (aq)
HClO= a weak acid that disinfects and kills microorganisms in water
what is chlorine plus water an example of
a disproportionation reaction- this is because chlorine is being oxidised and reduced
what is a precipitation reaction? (DNTK)
a reaction in which two ionic solutions are mixed to give an insoluble compound.
carbonate ion test
- react with acid, if fizzing occurs, bubble gas through limewater- if turns cloudy co2= present so carbonate ions were present
sulphate ion test
add HCl and a few drops of BaCl2
positive result: a white precipitate formed (which is barium sulphate)
halide ion test
-acidify the solution with dilute nitric acid to prevent other insoluble salts from forming
-add silver nitrate and note the colour of precipitate
- as the colours are hard to distinguish then add the following
-dilute ammonia solution then conc. ammonia solution
Cl- = white
Br- = cream
I- = yellow
ammonium ion test
-add NaOH to the substance to be tested.
-Heat (ideally in waterbath) so they react
-place a damp red litmus paper to the solution to observe
positive result:
-damp litmus paper turns blue
-strong and distinctive smell given off
what order does the ion test go in
CARBONATES then SULFATES then HALIDES
why are carbonates tested before sulfates?
barium sulphate is a white precipitate but so is barium carbonate so carbonates must be ruled out first before sulphate test
why are sulphates tested before halides
silver nitrate reacts with sulphates to form a precipitate so sulphates must be ruled out before the halide test
if you intend to test for sulfate or halide ions, whats important?
its important to use dilute nitric acid for this test because sulfuric acid contains sulphate ions and hydrochloric acid contains chloride ions, which will show up in the sulfate and halide tests
what reaction demonstrates the decrease in reactivity as you go down group 7
displacement reactions
method for displacement reactions
add:
- halide ( e.g potassium bromide)
- halogen (e.g chlorine/ chlorine water)
- cyclohexane
where will the more reactive halogen end up (displacement reaction)
in the bottom layer
what colour does iodine turn with cyclohexane
purple
what colour does bromine turn with cyclohexane
orange
what colour does chlorine turn with cyclohexane
pale yellow
write the equation for chlorine reacting with alkali ( cold and dilute aq sodium hydroxide), what type of reaction is this?
2NaOH(aq) + Cl2 (g) ==> NaCl(aq) + NaClO(aq) +H20(l)
NaOCl(aq)= bleach
this is a disproportionation reaction as chlorine is oxidised and reduced
what are the conditions for chlorine reacting with sodium hydroxide
sodium hydroxide has to be cold and dilute
and it has to be aq
what happens when you add dilute ammonia solution then conc ammonia solution to chloride ion
solubility in dilute ammonia solution: soluble
solubility in conc ammonia solution: soluble
what happens when you add dilute ammonia solution then conc ammonia solution to bromide ion
solubility in dilute ammonia solution: insoluble
solubility in conc ammonia solution: soluble
what happens when you add dilute ammonia solution then conc ammonia solution to iodide ion
solubility in dilute ammonia solution: insoluble
solubility in conc ammonia solution: insoluble
when do neutralisation reactions occur
when H+ ions donated by an acid react with OH- ions donated by a base
what does complete combustion result in?
CO2 and H20
whats the ion responsible for bleaching
ClO-
does be react with oxygen
no
does silver sulphate produce a precipitate?
yes
