Bonding And Structure

Question 1

What does a polar covalent bond look like?

Answer 1

There is a difference in electronegativity so bonding electrons are shared unequally between 2 atoms and there are partial charges on atoms

Question 2

What should occur for a molecule to be considered polar?

Answer 2

-must contain polar bonds
-dipoles on the bonds shouldn’t be cancelled out through symmetry(molecule must be non symmetrical)

Question 3

What is ionic bonding?

Answer 3

The electrostatic attraction between oppositelt charger ions

Question 4

What are solid ionic compounds arranged in

Answer 4

A giant lattice

Question 5

What is an ionic lattice

Answer 5

A structure with a repeating pattern of oppositely charged ions

Question 6

What are some key points for dot and cross diagram

Answer 6

-Ions have square brackets around them
-charges must be shown

Question 7

Define covalent bonding

Answer 7

Electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms

Question 8

What is the 8 electron rule?

Answer 8

-The elements C,N,O and F always end up with 8 electrons in their outer shell. This is the most stable arrangement for them
-many elements can have more than 8 electrons in their outer shell

Question 9

What is a dative(co ordinate bond) covalent bond?

Answer 9

A covalent bond where both of the shared electrons come from the same atom

Question 10

What does each added lone pair reduce the bond angle by?

Answer 10

2.5°

Question 11

What does electronegativity refer to?

Answer 11

-the ability of an atom to attract a bonding pair of electrons in a covalent bond

Question 12

What is the general trend in periodic table for electronegativity?

Answer 12

-elements get more electronegtauve from left to right and from bottom to top
-fluorine is the most electronegative

Question 13

What are some factors that affect electrostatic attraction?

Answer 13

-charge on the nucleus
-shielding
-distance between the nucleus and the electrons in the bond

Question 14

Describe the charge on the nucleus trend in periodic table

Answer 14

-As we go from left to right across a period, the charge on the nucleus increases(more protons are added to the nucleus)
-hence the attraction between the nucleus and the bonding electrons increases
-hence the electronegativity increases
-charge on nucleus increases aa you go down group but electronegativity does not increase due to shielding

Question 15

Describe the trend in shielding in periodic table

Answer 15

-increases down the group
-reduces attraction between the nucleus and bonding electrons

Question 16

Describe the distance between nucleus and bonding electrons

Answer 16

-across a period(left to right) distance between nucleus and bonding electrons descreases(increasing nuclear charge same shielding so increased attraction between them)
-down a group(top to bottom) distance between nucleus and bonding electrons increases(more shells)

Question 17

What us a non polar covalent bond

Answer 17

-same electronegativity
-bonding electrons are shared equally between 2 atoms
-no charges on atoms

Question 18

What are the 3 intermolecular forces

Answer 18

-London forces(Van der Waals forces)
-Permanent dipole-dipole interactions
-hydrogen bonds

Question 19

how are london forces created

Answer 19

-movement of electrons produces a changing dipole in a molecule.
-an instantaneous dipole will exist but its position is constantly shifting
-the instantaneous dipole induces a dipole on a neighbouring molecule
-the induced dipole induces further dipoles on neighbouring molecules which then attract one another

Question 20

How do London forces get stronger?

Answer 20

-the more electrons there are, the stronger the London force get

Question 21

why do the london forces get stronger as there are more electrons?

Answer 21

-can create a larger transient dipole which creates larger transient dipoles on other molecules
-larger dipoles mean a stronger force of attraction between molecules

Question 22

How can a substance be evaporated?

Answer 22

-intermolecular forces must be broken
-the stronger the intermolecular forces, the more energy required to break them
-so the higher the boiling point

Question 23

What forces do all molecular substances have?

Answer 23

-London forces of attraction
-usually very weak and don’t require much energy to overcome
-other types of IMF are usually stronger

Question 24

Permanent dipole-dipole forces

Answer 24

-if molecules posses an overall permanent dipole, these dipoles can interact

Question 25

Which forces are stronger, London forces or permanent dipole dipole forces?

Answer 25

Permanent dipole dipole forces tend to be much stronger

Question 26

when does hydrogen bonding occur?

Answer 26

-occurs between a hydrogen atom which is bonded to O, N or F and the lone pair of electrons on the very electronegative atom(o,N of F)

Question 27

What unique properties does hydrogen bonding give to water?

Answer 27

-surface tension
-excellent solvent
-liquid at room temperature

Question 28

Hydrogen bonding-ice

Answer 28

-each water molecule is bonded to 4 others in a tetrahedral formation
-volume is largee than the liquid
-when ice melts the structure collapses slightly and the molecules come closer which is why ice floats

Question 29

Why do ionic compounds have high melting points?

Answer 29

-strong ionic bonds which require a lot of energy to overcome

Question 30

Why can ionic compounds dissolve in water?

Answer 30

-water is polar therefore can form electrostatic forces of attraction to the dissolved ions

Question 31

define a lattice

Answer 31

-regular repeating pattern of particles

Question 32

what is a simple molecular lattice?

Answer 32

-regular repeating pattern of molecules

Question 33

What forces must be broken to melt(or evaporate) a simple molecular lattice

Answer 33

-London forces

Question 34

Why do simple molecular substances have low melting points?

Answer 34

-lattice is held together by relatively weak intermolecular forces, which don’t require much energy to overcome

Question 35

What molecules will polar solvents dissolve

Answer 35

-polar molecules

Question 36

what molecules will non polar solvents dissolve

Answer 36

-non polar molecules

Question 37

why do non polar solvents only dissolve non polar molecules?

Answer 37

-they only have london forces acting between them so they can form the same weak interactions with a non polar solvent

Question 38

Why don’t polar solvents dissolve non polar molecules?

Answer 38

-polar solvents have stronger permanent dipole dipole interactions between the molecules so mixing non polar molecules in with this will disrupt these forces, so non polar substances do not dissolve in polar solvents

Question 39

Why don’t simple molecular substances conduct electricity as a solid, liquid or solution

Answer 39

-they do not contain mobile electrons or ions so they cannot conduct electricity