Module 3 AS Need To Know Flashcards
Features of periodic table then
Then = in increasing atomic MASS, elements lined up with similar properties , gaps were left for predictions for elements yet to be discovered
How is periodic table arranged now?
- In increasing ATOMIC NUMBER
- in periods with similar chemical and physical properties (periodicity )
- in groups having similar chemical properties
Periodcitiy definition
Examples
Repeating trends across periods, such as
- ionisation energy , electric configuration , melting points structure
Ionisation energy
First
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
What is electron shielding ?
What is effect of increased shielding
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
General trend across a period for ionisation energy
WHAT MUST SAY
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
When going down a group, why even tho nuclewr chsrge increased ionisation energy decreases
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
Going across period 2 and 3, overall trend is ionisation energy increases
When are 2 points it dips and why!
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
Describe general graph of ionisation energies starting from hydrigen across periods
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
Graphene vs graphite
Why can conduct electricity
Structure of graphite And thus boiling point?
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
Trend in melting points across period 2 and 3
P4 and s8?
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 …
What is group 2 reactivity lower group and why?
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
Trend of group 2 metal hydroxides down the group? (2)
(Attrvwtuon to ions less therefore…)
More ions released in solution, thus MORE SOLUBLE , and HIGHER PH (more alkaline)
How is group 2 alkali hydroxides used in agriculture and indigestion
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
Why is ‘milk of magnesia’ group 2 base for antacid being slightly soluble useful
Soluble enough to get to stomach but not soluble enough to pass through system
What is the trend in melting snd boiling point of halogens and WHY
what do they exist as?
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
Appearances of halogens at RTP and states?
What about iodine !
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
Halogen displacment reactions colours
In cyclohexane?
Why we use cyclohexane
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
Trend in reactivity for halogens down grouo and WHY
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
Disproportionation DEFINITON
in a redox resction the same species gets both oxisided and reduced
1) Chlorine and water disproritnstion
Products
- what is used to treat water
- what else does it act as
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
How does chlorine and water disprortiantion reaction act like bleach
acts as a weak bleach.
= add water to chlorine, and indicator
Becomes red due to two acids, then becomes white due to BLEACH
2) chlorine NaOH diprortinstion
What is specific CONDITION FOR NAOH
what is produced used for
NaOH COLD AQEUOUS DILUTE + cl2 = NACLO + NACL + H2O
Naclo is used as household bleached
Chlorine benefit and used for water treatment
Benefit
RISK (key word ) and why is the risk made
- 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
