Bonding (Covalent)

Question 1

What is a covalent bond?

Answer 1

A shared pair of electrons between 2 atoms (usually 2 non metals?

Question 2

How are covalent bonds represented?

Answer 2

By drawing lines from one atom to the other ( 1 line for each covalent bond)

Question 3

What is the bond length?

Answer 3

When 2 nuclei are at a particular distance away from each other so that the attractive and repulsive forces are balanced. (Nuclei stay at a fixed position at that distance)

Question 4

What si a dative covalent bond?

Answer 4

A type of covalent bond where the pair of electrons in the bond are supplied by one of the atoms

Question 5

How are dative covalent bonds represented?

Answer 5

An arrow from the atom providing the pair of electrons to the atom receiving them

Question 6

What 5 things are classed as a charge clouds?
How many charge clouds do they each represent?

Answer 6

Lone pair of electrons
Single covalent bond
Double covalent bond
Triple covalent bond
Dative covalent bond

All one charge cloud

Question 7

What does the shape of covalently bonded species depend on?

Answer 7

The number of pairs of electrons and the number of lone pairs around the central atom

Question 8

What is the relation between the number of lone pairs and the bond angle?

Answer 8

As the number of lone pairs increases the bond angle decreases because of their mutual repulsion

Question 9

What is the electron repulsion theory?

Answer 9

The mutual repulsion is minimised when the pairs of electrons are as far apart as possible

Question 10

What bonding pairs have the weakest to strongest repulsion?

Answer 10

Weakest is bonding with bonding
Middle is bonding with lone
Strongest is lone pair and lone pair

Question 11

Why is the bond angle practically 120 degrees in molecules with 3 charge clouds where there are 2 bonding pairs and 1 lone pair?

Answer 11

There are 2 double covalent bonds so there is a stronger mutual repulsion so the lone pair can’t push them closer together

Question 12

How do you calculate the number of charge clouds?

Answer 12

(Group number of central atom + number of bonds) + negative charge or - positive charges

Divided by 2

Question 13

What is electronegativity?

Answer 13

The power of an atom to attract the pair of electrons in a covalent bond towards itself

Question 14

Why is electron density not shared equally in covalent bonds?

Answer 14

The atoms have different electronegativities

Question 15

What 2 factors affect electronegativity?

Answer 15

Nuclear charge
Size of the atom

Question 16

How does nuclear charge affect electronegativity?

Answer 16

The higher the nuclear charge (number of protons) the higher the electronegativity as the atom is able Yk attract electrons more

Question 17

How does the size of the atom affect electronegativity?

Answer 17

The smaller the atomic radius the higher the electronegativity because the electrons are closer to the nucleus so they are attracted to it more / stronger attraction

Question 18

How does electronegativity change as you go down a group?

Answer 18

It decreases because
Atomic radius increases
Shielding increases (no effect)

Question 19

How does electronegativity change as you go across a period?

Answer 19

It increases because

Atomic radius decreases
Nuclear charge increases
Shielding almost constant no effect

Question 20

What is a polar bond?

Answer 20

An unequal distribution of the pair of electrons in a covalent bond

Question 21

What is a dipole?

Answer 21

A difference in charge between 2 atoms caused by a shift in electron density in the bond between the atoms so polar bond

Question 22

What is the relation between electronegativity difference and polarisation?

Answer 22

The higher the electronegativity difference the greater the polarisation

Question 23

What are 2 conditions where you would have a non polar bond?

Answer 23

When the 2 atoms covalently bonded are the same so they have the same electronegativity

When the difference in electronegativity is less than 0.4

Question 24

What is an asymmetrical molecule?

Answer 24

When the dipoles are not the same in different directions so they don’t cancel each other out which results in an overall permanent dipole moment

Question 25

What is a symmetrical molecule?

Answer 25

When the dipoles are the same in all the different directions so they cancel each other out which results in no permanent dipole moment

Question 26

What are 3 conditions for a symmetrical molecule?

Answer 26

No lone pairs

All atoms around central atom must be the same

All bonds around central atom must be the same ( eg all single covalent )

Question 27

How do you predict bonding by looking at difference in electronegativity?

Answer 27

0% - covalent
25% - predominately covalent
50% - polar covalent
75% - predominantly ionic
100% - ionic

Question 28

How do you calculate the % difference in electronegativity?

Answer 28

Difference in electronegativity divided by 3.3 multiplied by 100

Question 29

When do you get Van Der Waals forces?

Answer 29

When the molecules are non polar (have the same electronegativity or less than 0.4)

Question 30

Describe the van der waals attraction between forces

Answer 30

Since electrons are always moving the molecules create temporary dipoles which indices a dipole in neighbouring molecules (because of the slight charges)

Question 31

What is the relation between van der waals forces and boiling points?

Answer 31

The more that there are or the stronger they are the higher the boiling points

Question 32

What are 2 factors which increase the strength of van der waals forces?

Answer 32

How many electrons there are (more = stronger)

The size of the molecule ( large = more forces )

Question 33

Why does a higher number of electrons increase the strength of can der waals forces?

Answer 33

It means that there is greater opportunities for and induced dipole to be seto up

Question 34

Why do straight chain alkanes have stronger van der waals forces than branched alkanes?

Answer 34

They are packed closer together therefore it creates more points of contact between molecules which allowed for more dipoles to be indices resulting in more and stronger forces

Question 35

When do permanent dipole dipole forces happen?

Answer 35

Only occurs in polar molecules (electronegativity difference is higher than 0.4 or is 0.4)

Question 36

When do you get permanent dipole dipole forces and van der waals forces together?

Answer 36

When the polar molecule has an overall permanent dipole (asymmetrical)

Question 37

Describe the attraction in permanent dipole dipole forces

Answer 37

The unequal distribution of charge is permanent as the more electronegative atom always has a higher share of electrons

Question 38

What are the conditions for hydrogen bonding?

Answer 38

There must be hydrogen present
The hydrogen must be directly covalently bonded to either oxygen, fluorine or nitrogen

Question 39

How do you draw a hydrogen bond?

Answer 39

A dotted line between the lone pair of electrons of the central molecule and the hydrogen with the delta plus charge

Question 40

Define a permanent dipole dipole force

Answer 40

Electrostatic force of attraction between polar molecules

Question 41

What are 2 properties of simple molecular substances?

Answer 41

Low melting and boiling point
Can’t conduct electricity

Question 42

Why is water more dense than ice

Answer 42

In ice all the water molecules are hydrogen bonded and hydrogen bonds tend to be long so the h20 molecules are further apart
In water not all hydrogen bonded so close together which causes higher density