Elements of Life - Molecular Structure

Question 2

What is the bond angle for tetrahedral molecules?

Answer 2

109.5

Question 3

Why is H₂O a bent molecule?

Answer 3

It has 2 bonding and 2 non-bonding pairs of electrons.

They all repel to be as far apart as possible, but the non-bonding pairs repel stronger, therefore we get a bent shape with a 104.5 angle

Question 4

What is the bond angle of a trignal planar molecule?

Answer 4

120

Question 5

What is the bond angle of a linear molecule?

Answer 5

180

Question 6

What is the bond angle of an octahedral molecule?

Answer 6

90

Question 7

What are the bond angles for trignal bipyriamidal molecules?

Answer 7

90 and 120

Question 8

What is the rule for calculating bond angles when a molecule has lone pairs of electrons?

Answer 8

reduced by 2.5 for every lone pair

Question 9

If a molecule has 6 paired electrons what shape will it assume?

Answer 9

octahedral

Question 10

If a molecule has 5 electron bonding pairs, what shape is it?

Answer 10

trignal bipyramidal

Question 11

Which equation links moles, mass and relative atomic mass?

Answer 11

Moles = mass / molar mass

Question 12

Define an emperical formula

Answer 12

the ratio of atoms is a compound

eg C₂H₆ would have be empirical formula of CH₃

Question 13

Define a molecular formula

Answer 13

The actual number of atoms in a molecule

eg C₂H₅OH would have the molecular formula of C₂H₆O

Question 14

What is the general formula for percentage bymass?

Answer 14

atomic mass of elements in compound / atomic mass of compound

x 100

Question 15

Define water of crystallisation

Answer 15

When H₂O molecules are present inside crystals but not bonded within the structure

Question 16

Define electronegativity

Answer 16

The tendency of an element to attract electrons in covalent bonds

Question 17

What determines whether a bond is ionic or covalent?

Answer 17

The differences of electronegativity between the elements

big difference -> ionic -> one can pull electrons a lot stronger

medium -> polar covalent

small -> covalent

Question 18

Which elements does aluminum only form ionic bonds with?

Answer 18

F and O

Question 19

Which group of elements will never form a covalent bond and why?

Answer 19

Group 1

they are too far apart from other elements

Question 20

List the properties of ionic compounds

Answer 20

• > all solids at room temperature
• > high melting and boiling points
• > form giant ionic lattices
• > conduct electricity when liquid or aqueous
• > SOME dissolve in water but not all

Question 21

List the insoluble ionic compounds

Answer 21

• > barium, lead, calcium and silver sulphates
• > silver and lead halides
• > metal carbonates
• > metal hydroxides (excluding group 1 and ammonium)

Question 22

Define a dative covalent bond

Answer 22

When both bonding electron originate from the same atom

Question 23

What is the solubility of nitrate ions?

Answer 23

Always soluble in water