Module 3 AS Need To Know

Question 1

Features of periodic table then

Answer 1

Then = in increasing atomic MASS, elements lined up with similar properties , gaps were left for predictions for elements yet to be discovered

Question 2

How is periodic table arranged now?

Answer 2

• In increasing ATOMIC NUMBER
• in periods with similar chemical and physical properties (periodicity )
• in groups having similar chemical properties

Question 3

Periodcitiy definition

Examples

Answer 3

Repeating trends across periods, such as
- ionisation energy , electric configuration , melting points structure

Question 4

Ionisation energy
First

Answer 4

Is the energy needed to remove one electron off one mole of gaseous atoms to form one mole of gaseous 1+ ions

2nd is one electron from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

Question 5

What is electron shielding ?

What is effect of increased shielding

Answer 5

With addition of electron shells means more electrons, and these are negatively chsrged they will repel each other

This reduces attraction between nucleus and balance shell electrons , so increased shielding reduces ionisation energy

Question 6

General trend across a period for ionisation energy

WHAT MUST SAY

Answer 6

Increases
- increased nuclear charge
- decreased atomic radius
- shielding IS SIMILAR (MUST SAY)

These all increase nuclear attraction to valence shell electrons, so more energy is needed to remove an electron thus ionisation energy increases

Question 7

When going down a group, why even tho nuclewr chsrge increased ionisation energy decreases

Answer 7

Radius increases + electron shielding , these effect it much more, so nuclear attraction decreases therefore less energy needed to remove electron and so ionisation energy DECREASES

Question 8

Going across period 2 and 3, overall trend is ionisation energy increases

When are 2 points it dips and why!

Answer 8

1) between group 2 and 3
- group 3 is the first time an electron is filled in p sub shell .
- o sub shell is a higher energy level than the s sub shell, it is EASIER TO REMOVE AN ELECTRON than the s sub shells, so ionisation energy increases

2) between group 5 and 6
- at group 5 3 electrons are in 3 separate p orbitals to reduce repulsion
- in group 6 the 4th electron must be filled in another p orbital in oppsite spin.
- this INCREASED REPULISON makes it easier to remove electron from group 6 than one before
So ionisation energy decreases

Question 9

Describe general graph of ionisation energies starting from hydrigen across periods

Answer 9

Goes up to helium, then sharp decrease due to shielding and raidus, general increase with dips, then sharp decrease

Remember the second peak for noble gas MUST be smaller than first one is more shielding snd radius

Question 10

Graphene vs graphite
Why can conduct electricity
Structure of graphite And thus boiling point?

Answer 10

1) grapheme is a SINGLE LAYER OF GRAPHITE
2) graphite and broaden formed as CARBIN uses 3 electrons to form covalent bonds with other carbkn atoms , and 4th is delocalised thus can carry current

3) graphite are layers of graphene on top of each other which are bonded by WEAK LONDON FORCES THEREFORE LOW MELTING BOILING

Question 11

Trend in melting points across period 2 and 3

P4 and s8?

Answer 11

Starts metallic binding so increases
Peaks at grouo 4 because giant Covalent
As soon as it touches grouo 5sharp decrease due ti simple covslent

2) however period 3 it goes to p4 which is higher melting than just P due to more electrons and thus stringer London forced and more of them
- and then this INCREASES TO S8 for same reason
- and finally decrease again

Noble is the lowest as just single atom covslent …

Question 12

What is group 2 reactivity lower group and why?

Answer 12

Increases
- to become a 2+ ion requires input of 2 ionisation energies
- lower group increased shielding and atomic radius = lower ionisation energy
- thus more reactive and stringer reducing agent

Question 13

Trend of group 2 metal hydroxides down the group? (2)

Answer 13

(Attrvwtuon to ions less therefore…)

More ions released in solution, thus MORE SOLUBLE , and HIGHER PH (more alkaline)

Question 14

How is group 2 alkali hydroxides used in agriculture and indigestion

Answer 14

1) lime in the form Ca(OH)2 is used to neutralise acidic soils
2) Mg(Oh2) / CaCo3 used to neutrilsi HCL in stomach as antacids for ACID INDIGESTION

Question 15

Why is ‘milk of magnesia’ group 2 base for antacid being slightly soluble useful

Answer 15

Soluble enough to get to stomach but not soluble enough to pass through system

Question 16

What is the trend in melting snd boiling point of halogens and WHY

what do they exist as?

Answer 16

Exist as diatomic atoms

• increased boiling point
  = because 1) more electrons lower you go
• thus greater INSTANEOUS dipole at any instant
• thus greater induced dipole
• thus stringer induced dipole dipole interactions
• thus more energy needed to overcome

= higher boiling point

Question 17

Appearances of halogens at RTP and states?
What about iodine !

Answer 17

F2 = pale yellow
Cl2 = pale green (ww2)
BR2 (orange brown liquid )
I2 (black grey solid which sublimed to form GAS (this was in a question!)

AT 2 never been seen

Question 18

Halogen displacment reactions colours
In cyclohexane?

Why we use cyclohexane

Answer 18

More reactive halogen will displace a less one and kick that out showing That’s colour

2) as it halogens dissolve more readily and show colours better, could be hard to differentiate iodine and bromine

Chlorine = pale green, ti pale green

Bromine = orange to orange

Iodine = brown to violet

Question 19

Trend in reactivity for halogens down grouo and WHY

Answer 19

Less reactive

Needs to attract an electron to form an ion
- going down the group :
- electorn shielidng increases + atomic radius
= less nuclear attraction
= harder to attract an electron
Thus less reactive

Question 20

Disproportionation DEFINITON

Answer 20

in a redox resction the same species gets both oxisided and reduced

Question 21

1) Chlorine and water disproritnstion

Products
- what is used to treat water
- what else does it act as

Answer 21

Forms Cl2 +H2O forms HCLO + HCL

• chloric acid and chlorate ions are the one that kill bacteria , not hcl
• acts as a weak bleach.
  = add water to chlorine, and indicator
  Becomes red due to two acids, then becomes white due to BLEACH

Question 22

How does chlorine and water disprortiantion reaction act like bleach

Answer 22

acts as a weak bleach.
= add water to chlorine, and indicator
Becomes red due to two acids, then becomes white due to BLEACH

Question 23

2) chlorine NaOH diprortinstion

What is specific CONDITION FOR NAOH
what is produced used for

Answer 23

NaOH COLD AQEUOUS DILUTE + cl2 = NACLO + NACL + H2O

Naclo is used as household bleached

Question 24

Chlorine benefit and used for water treatment

Benefit
RISK (key word ) and why is the risk made

Answer 24

• benefit is can kill bacteria to make water safe to drink
• however chlorine left in water csn react with hydrocarbons to produce CHLORINATED HYDROCARBONS which are CARCINOGENIC

However without chlorine no clean water , it’d long so still good

Question 25

Standard enthalpy change of reaction

Answer 25

Enthlapy change that accompanies s reaction based on the molar quantities of equation with reactant and product under standard state

Question 26

Standard enthlapy change of formation

Answer 26

Enthalpy change that takes place one 1 mole of a COMPOUND is formed from its constituent elements,
With all reactants and products in standard states

Question 27

Standard enthalpy change of combustion

Answer 27

Enthlapy change that accompanies one mole of reactant reacts comoelltey with oxygen

Undertr standard condtions , stated

Question 28

Standard enthlapy neutrlisation

Why is this same for any neutralisation

Answer 28

Enthlapy change that accompanies the reaction of an acid and base to form ONE MOLE OF H2O

If making one mole h2O each time must be H+ + Oh- = H2O, this gives a constant enthalpy for any neutrilisation reaction , don’t lack

Standard states and conditions

Question 29

Summary standard reaction formation combustion neutrilisation

Where the 1

Answer 29

Reaction is enthlapy Change of reaction based on molar quantities

Formation is formation of one mole (product ) under constituent states

Combustion is one mole reactant COMPLETLEY react with oxygen

Neutrilisation is acid by base one mole water

Formation 1 product combustion 1 reactant neutrilisation 1 h2o

Question 30

3 reasons for less Exothermic value then expected and why ?

1 reason for more or less?

Answer 30

Value = mC AT x FM / mass fuel

1) heat loss to surroundings ( more mass needed)
2) incomplete combustion of fuel (more mass needed)
3) evaporation from wick ( more mass needed)

4) NON SGANDARD STATES could give more or less

Question 31

Average bind enthlapy 2 limitations why can’t give you the actual enthalpy of reaction

Answer 31

1) is an average, for a specific system the bond enthalpies are different , but it’s an average
2) will give you the answer assuming everything is gas, when the standard reaction might need a resctsnt as a liauidnetc

Question 32

Why is it so hard to emadure enthalpy change of reactions directly (3) and thus use Hess law?

REMEMBER

Answer 32

• rate of reaction could be too slow
• activation energy too high
• so many side compounds would be ,add it’s impossible to actually measure

Question 33

Why does ror max at t=0 and decreases as time goes on

Answer 33

Because most reactant at t=0 and conc increases ror, as t progresses conc decreases so does rate

Question 34

Why are catalysts really IMPORTSNT sustainability wise

Why we still use even tho some are toxic

Answer 34

By lowering temperatures, it lowers energy demands to achieved same chemical processes

• this means less combustion of fossil fuels is used, resulting in less co2 emissions

2) we still use cstksydtd because their toxic vitu is outweighed by thr envionemtsl benefits

Question 35

What does area under Boltzmann show?

Answer 35

The TOTAL NUMBER OF MOLECULES

Question 36

Dynamic EQUILIBRIUM features 3 SPEC POINTS

Answer 36

• rate of forward reaction = rate of backward reactions
• closed system
• concentrations of products and reactants are FIXED
  ( but not necessarily the same)

Question 37

What effect does calayst have on EQUILBKRUM 2 points

Answer 37

Increases rate of forward and backward reaction

Dynamic EQUILBKRUM achieved fsdter

Question 38

What should you do for comprised in chemical processes

Easy way to increase effeicnt?

Answer 38

High enough pressure for good rwte but not too expense
High temp for good rate but not position EQUILBKRUM

Use a catlsydt if can, try recycle waste product to increase atom economy too