Chapter 2: Bonding

Question 1

What are the 3 types of IMF in increasing strength?

Answer 1

van der Waals (weakest)
dipole-dipole
hydrogen bonding

Question 2

What are van der Waal forces?

Answer 2

• they exist in ALL molecules

- force of attraction

Question 3

How do van der Waal forces work?

Answer 3

• at any point, more electrons on one side of atom than the other, so electron density is higher on one side
• this creates a temporary dipole which causes attraction between mol.
• the dipoles are temp. because electrons are always moving so dipoles can flip at any time
• this causes an overall effect of attraction

Question 4

How do van der Waals and mp/bp change with size of molecule?

Answer 4

the larger the mol. = more electrons = stronger vdw forces, therefore, more energy is required to overcome the forces, so larger mol, have higher mp/bp

Question 5

What state is butter at room temperature?

Answer 5

solid, made of saturated fats, straight chains
can pack more tightly together, stronger vdw
higher mp/bp

Question 6

What state is olive oil at room temperature?

Answer 6

liquid, made of unsaturated fats, branched chains, do not lie close together, weaker vdw forces, less energy required to overcome, lower mp/bp

Question 7

When do dipole-dipole forces occur?

Answer 7

When partial charges (delta +, delta -) are always present, due to the difference in electronegativities
forces of ATTRACTION between opp. charged ends of a dipole

Question 8

When does hydrogen bonding occur?

Answer 8

attraction between lone pair of an O, N or F atom and δ + hydrogen
H must be bonded to O, N or F
ONF are electronegative, but H isn’t, so causes a polar bond

Question 9

Why does water expand when frozen?

Answer 9

when undergoing freezing, more hydrogen bonds are being formed which leads to a regular, LATTICE structure which means water mol. are more spread out so it expands and has lower density than water

Question 10

What is the trend of mp down group 6/7 when bonded to hydrogen?

Answer 10

H₂O and HF have H bonding so high mp as forces are very strong
then there’s a large drop because no hydrogen bonding is present
but then there is an increase, because down the group, the size of the mol. increases so stronger vdw forces

Question 11

Suggest the strongest type of IMF between CCl₂F₂?

Answer 11

vdw - yes
dipole-dipole - yes
H bonding - no
answer: dipole-dipole

Question 12

State the strongest IMF between methane?

Answer 12

no ONF so no hydrogen bonding
no halogens so no large diff. in electronegativities so no dipole-dipole
answer: dipole-dipole

Question 13

Although phosphine mol. contain hydrogen atoms, there is no hydrogen bonding, suggest why?

Answer 13

H
H - P- H
Phosphorus is not very electronegative so not big enough of a difference of electronegativities between P and H for hydrogen bonding to occur

Question 14

Do metals/nonmetals have large/small electronegativities?

Answer 14

metals typically have low electronegativity

non-metals typically have high electronegativites

Question 15

What is ionic bonding?

Answer 15

bonds between metals and non-metals
it is the electrostatic attraction between oppositely charged ions acting in all directions,
forms a giant, ionic crystal lattice

Question 16

What are the properties of ionic compounds?

Answer 16

• high mp/bp because lots of energy required to break strong electrostatic forces of attraction
• conducts electricity when molten, because ions become free to move and carry charge
• brittle- layers cannot slide over each other

Question 17

What is covalent bonding?

Answer 17

the sharing of one or more pairs of electrons between non-metals
macromolecular
simple molecular

Question 18

How does diamond bond?

Answer 18

each carbon of atom is covalently bonded to 4 other C atoms

Question 19

How does graphite bond and what are its properties?

Answer 19

each C atom is covalently bonded to 3 C atoms, 1 delocalised electron per atom of C. arranged in LAYERS
-slippery- weak van der Waal forces between layers

Question 20

Why do macromolecular substances have high mp/bp?

Answer 20

MANY. STRONG covalent bonds between all atoms

Question 21

Do macromolecular substances conduct electricity?

Answer 21

no because there are no free electrons or mobile ions carry charge

Question 22

What is the A-level rule for covalent bonding?

Answer 22

central atoms can promote electrons between orbitals in the same principal energy level
but this promotion requires energy

Question 23

How can you tell how many covalent bonds the central atom will make?

Answer 23

number of unpaired e⁻ = number of bonds that atom can make

Question 24

What is metallic bonding?

Answer 24

electrostatic attraction between positive central ions and negative delocalised e⁻
arranged in a regular lattice structure

Question 25

What is a dative covalent bond/coordinate bond?

Answer 25

-when the shared pair of electrons in the covalent bond

come from only one of the bonding atoms

Question 26

When is ionic bonding stronger?

Answer 26

when the ions are smaller and/ or have higher

charges

Question 27

What is electronegativity?

Answer 27

the power of an atom to attract the shared pair of electrons in a covalent bond

Question 28

How does metallic bond strength increase?

Answer 28

greater the charge of the ion, the stronger the metallic bonds because the ion is stronger so the electrostatic attraction to the delocalised electrons is stronger so more energy is required to overcome the forces of attraction

Question 29

NHF₂ + BF₃ ——-> F₂HNBF₃
State the type of bond formed between N and B in F₂HNBF₃
Explain how this bond is formed?

Answer 29

dative covalent bond

lone pair from N is donated to B to form a dative covalent bond

Question 30

Deduce when the bonding in nitrogen oxide is covalent rather that ionic?

Answer 30

this is because there is a small difference in electronegativity

Question 31

Suggest why titanium can be hammered into different shapes and why these objects with different shapes have similar strengths

Answer 31

layers of ions can slide over each other

they have similar strengths because they have the same metallic bond

Question 32

Explain why the mp of Al is higher than mp of Na?

Answer 32

Al has a greater charge and more delocalised e⁻ than Na therefore, it has a stronger force of attraction between the + ion and e⁻, requires more energy to break