chemistry key points

Question 1

(work through)
what is the AMOUNT of sodium carbonate in 16g

Answer 1

step 1) realise that amount refers to moles.

Step 2) 16g/106.0 = 0.151mol

Question 2

(work through)
how to score marks for metallic bonding

Answer 2

mark 1) state the difference in charge
e.g Al3+ Mg2+ Na+

mark 2) state the difference in delocalised electrons
e.g Al3+ & Mg2+ - Al has 1 more delocalised electron

Al3+ & Na+ - Al has 2 more delocalised electrons

mark 3) therefore more energy is required to break the metallic bonds

Question 3

why does PCl5 exist but NCl5 doesn’t?

Answer 3

it is due to PCl5 being able to expand it’s octet to allow 5 bonds to form

Question 4

explain why the first ionisation energy of X is lower than the first ionisation energy of Y

Answer 4

mark 1) talk about the electronic configuration

mark 2) electron shielding

Question 5

convert mol in gas to volume

Answer 5

1 mol of gas = 24 dm3 vol
mol x 24 = dm3
mol x 24000 = cm3

Question 6

Pv=nRT

Answer 6

P= pressure(Pa)
KPa -> Pa (x1000)

v= volume(m3)
dm3 -> m3 (/1000)
cm3 -> m3 (/1000000)

n=mol

R= gas constant (8.31 jmol-1 k-1)

T= temperature (kelvin)
0 degrees c = 273k

Question 7

the trend in ionisation energy along a period

Answer 7

along a period, ionisation energy increases due to increased nuclear attraction and decreasing atomic radius, meaning that the outer electron and nucleus are held more tightly therefore more energy is required to remove 1 mol of electron to ionise an ion

Question 8

reason for a decrease in ionisation energy down a group

Answer 8

down a group ionisation energy decreases because the nuclear attraction between the nucleus and the outer electron reduces & increasing amounts of shielding means that less energy is required to remove the outer electron