Bonding - exam & tutorial corrections

Question 1

Why less energy to break covalent bond between HI and HBr

Answer 1

• I has larger ionic radius
• more shells and electrons
• LONGER BOND (this is what I forgot to say in exam)
• so weaker attraction between nuclei and shared pair e-

Question 2

How to work out how to draw a dot and cross diagram for a polyatomic ion?

Answer 2

• work out number of valence electrons
• add in the correct amount of electrons for if you know there is a single/double/triple bond
• play around filling in electrons to fulfill number of outer shell electrons according to periodic table
• add in the extra electrons that make it an ion where it feels right

Question 3

What to do if stuck on drawing dot and cross diagram for ions?

Answer 3

think about the 3D structure and whether there are any double bonds, then you can work out how many dots and crosses go in that section

Question 4

How to work out how many valence electrons for a dot and cross ion drawing

and what else do you need?

Answer 4

count the number of outer shell electrons in each atom then add or subtract the number of electrons according to the ions overall charge

eg. CO3 2- = 4 + (6x3) + 2 = 24 valence electrons

SQUARE BRACKETS AND CHARGE OUTSIDE

Question 5

Why does NH4 + have a plus charge?

Answer 5

it has formed a bond with H+ using N’s lone pair, subsequently gaining a PROTON

Question 6

Explain why the hydrogen halides are gases at room temperature?

Answer 6

• they have boiling points that are low that room temperature
• because they have weak forces between the molecules
• so little energy is required to overcome them

Question 7

Explain trend in bond polarity of hydrogen halides down group 7

Answer 7

• it decreases
• because as you go down the atoms become less electronegative
• so smaller difference in electronegativities of the atoms (forgot this part in exam)