Bonding

Question 1

Define ionic bonding

Answer 1

Ionic bonding occurs between metals and non-metals. The oppositely charged ions are held together by strong forces of electrostatic attraction within a giant ionic lattice.

Question 2

The greater the ionic charge …

Answer 2

The greater the ionic charge, the stronger the electrostatic attraction and therefore the stronger the ionic bond.

Question 3

The smaller the ionic radius …

Answer 3

The smaller the ionic radius, the more tightly packed the atoms can be and therefore the stronger the ionic bond

Question 4

The higher the charge density

Answer 4

the stronger the ionic bond

Question 5

When are cations formed?

Answer 5

when elements lose electrons to become stable.
Generally, this happens to metals in groups 1, 2 and 3, each losing their respective number of electrons to become positively charged

Question 6

When are anions formed?

Answer 6

when elements gain electrons to become stable.

Generally, this happens to non-metals in groups 5, 6 and 7, each gaining 3, 2 or 1 electron(s) respectively to become negatively charged

Question 7

Why does ionic radius increase down a group?

Answer 7

Because extra electron shells are added

Question 8

What are isoelectronic ions?

Answer 8

Those that have the same electronic configuration

Question 9

Explain why for a set of isoelectronic ions, the atomic number increases, the ionic radius then decreases

Answer 9

due to the positive nucleus attracting the electrons more strongly hence drawing them nearer

Question 10

What is the melting and boiling points of ionic substances like?

Answer 10

High

Oppositely charged ions are held together with strong forces of electrostatic attraction within a giant ionic lattice

Question 11

Do ionic substances conduct electricity?

Answer 11

When solid, the ions are held in fixed positions within the lattice, but when molten/dissolved they are free to move and hence can carry a charge to form a current.

Question 12

Ionic substances- brittle

Answer 12

When put under strain, the lattice is disrupted and cations could be put over cations, and anions over anions. They would hence repel each other and the lattice would break.

Question 13

Ionic substances- solubility

Answer 13

Only soluble in polar substances like water, because the ions are charged so can be pulled apart by polar molecules but not by non-polar molecules

Question 14

What is the migration of ions?

Answer 14

Copper Chromate solution is dropped onto damp filter paper
Crocodile clips are connected to a power source and can then be connected to both sides of the paper
Electrolysis occurs causing the negative chromate anions to move to the positive anode, whilst the positive copper cations move to the negative cathode
The solution is green: blue colouring shows the copper ions, yellow colouring shows the chromate ions.
Ions must therefore be charged and able to move/’migrate’ whilst in aqueous solution

Question 15

Define covalent bonding

Answer 15

Covalent bonding occurs between non-metals only (usually). The positively charged nuclei and negatively charged shared pair of electrons between them are held together by strong forces of electrostatic attraction. This can be within a giant or simple covalent structure

Question 16

The shorter a bond…

Answer 16

the higher its bond enthalpy

Question 17

Explain electron density on bond length

Answer 17

In covalent bonding, there are attractive forces between the nuclei and shared electrons. There are also repulsive forces between the two nuclei and shared electrons in themselves

Hence, the distance between the two nuclei is a balance of all of these forces acting opposingly and this is what is defined as the bond length.

So therefore the bond will be shorter if there is more electron density of if the atom’s involved are smaller.

Question 18

Explain Valence Shell Electron Pair Repulsion Theory

Answer 18

All electrons are negatively charged. Therefore, their repulsion about a central atom determines the shape of simple molecules and ions because repulsive forces are so that they are kept to a minimum.

Lone pair-Lone pair > Lone pair-Bonding pair > Bonding pair-Bonding pair

Question 19

What do lone pairs cause bond angles to do?

Answer 19

Decrease by 2.5

Question 20

Describe the linear shape?

Answer 20

2 bonding pairs & 0 lone pairs 180˚ angles

Question 21

Describe the trigonal planar

Answer 21

3 bonding pairs & 0 lone pairs 120˚ angles

Question 22

Describe the angular shape?

Could also be described as bent or v shaped

Answer 22

2 bonding pairs & 1 lone pair

<120˚ *(119˚) angles

Question 23

Describe the tetrahedral shape

Answer 23

4 electrons and 0 lone pairs

109.5 angles

Question 24

Describe the trigonal pyramidal shape (tetrahedral shape)

Answer 24

3 bonding pairs & 1 lone pair

<109.5˚ *(107˚) angles

Question 25

Tetrahedral angular shape

Answer 25

2 bonding pairs & 2 lone pairs | <109.5˚ *(104.5˚) angles

Question 26

Trigonal Bipyramidal shape

Answer 26

5 bonding pairs & 0 lone pairs | 120˚ and 90˚ angles

Question 27

Seesaw shape

Answer 27

4 bonding pairs & 1 lone pair | *87˚ and 102˚ angles

Question 28

Distorted t shape

Answer 28

3 bonding pairs & 2 lone pairs | *87.5 angles

Question 29

Linear trigonal Bipyramidal

Answer 29

2 bonding pairs & 3 lone pairs | 180˚ angles

Question 30

Octahedral

Answer 30

6 bonding pairs & 0 lone pairs | 90˚ angles

Question 31

Square pyramidal

Answer 31

5 bonding pairs & 1 lone pair | *90˚ and 81.9˚ angles

Question 32

Square planar

Answer 32

4 bonding pairs & 2 lone pairs | 90˚ angles

Question 33

(Distorted) T-shaped | Octahedral

Answer 33

3 bonding pairs & 3 lone pairs No stable molecules known to exist

Question 34

Linear | Octahedral

Answer 34

2 bonding pairs & 4 lone pairs No stable molecules known to exist

Question 35

How to predict the shapes and bond angles of simple molecules and ions

Answer 35

1. First draw the Lewis structure of the ion/molecule. 2. Next the steric number (number of lone pairs add the number of atoms bonded to a central atom) can easily be identified from this. 3. This can be used to work out the electron distribution (2 = linear, 3 = trigonal planar, 4 = tetrahedral, 5 = trigonal bipyramidal, and 6 = octahedral) 4. Now the number of lone pairs should be taken into account to work out the final geometry of the ion/molecule.

Question 36

What is electronegativity?

Answer 36

Electronegativity is the ability of an atom to attract the bonding pair of electrons in a covalent bond. Informally, it can be described as ‘electron-pulling power’.

Question 37

How is electronegativity measured

Answer 37

It is measured on the Pauling scale with fluorine being the most electronegative element, followed by oxygen, chlorine and then nitrogen.

Question 38

Trends of electronegativity across a period and up a group

Answer 38

Increase

Question 39

What happens in purely covalent substances VS polar covalent substances

Answer 39

In purely covalent substances, the bonding electrons are shared completely equally between the two atoms In polar covalent substances, the bonding electrons are shared unequally between the atoms, which therefore have partial charges on them

Question 40

What happens in purely ionic substances?

Answer 40

In purely ionic substances, one or more electrons are transferred completely from one atom to another, and therefore the atoms have full charges

Question 41

What is the general rule for electronegativity

Answer 41

a difference in electronegativity less than 0.4 results in pure covalent bonds; between 0.4 and 1.7 results in polar covalent bonds, and above 1.7 results in ionic bonds

Question 42

What is a dipole

Answer 42

A dipole is a difference in charge between the two atoms in a polar bond caused by a shift in electron density in the bond towards the more electronegative element.

Question 43

What does being a polar molecule depend on

Answer 43

The presence of polar bonds | The geometry/symmetry of the molecule

Question 44

If polar bonds are present and the molecule is symmetrical is the molecule present?

Answer 44

NO

Question 45

If polar bonds are present and the molecule is asymmetrical, is the molecule polar?

Answer 45

YES

Question 46

What are instantaneous dipole-induced dipole bonds called?

Answer 46

London forces

Question 47

Explain the existence of instantaneous dipole-induced dipole bonds

Answer 47

Electrons move around quickly and randomly and can be thought of as a cloud of charge about the nucleus. At any particular point in time, it is unlikely that the electrons will be evenly distributed and rather that they are more likely to be found on one side This is an instantaneous dipole where the area concentrated with electrons is partially negative and the area with an absence is partially positive This dipole is able to induce a dipole in a neighbouring atom/molecule

Question 48

How can dipoles be created/destroyed instantaneously?

Answer 48

because the particles are moving constantly as well as the electrons, causes an overall electrostatic force of attraction

Question 49

London forces are the ...

Answer 49

weakest type of intermolecular force and affects all atoms/ molecules

Question 50

Where do permanent dipole-permanent dipole bonds occur

Answer 50

in molecules that contain polar bonds but are asymmetrical There is electrostatic attraction between the poles of neighbouring molecules. This occurs in addition to instantaneous dipoles

Question 51

Are permanent dipole-dipole bonds stronger than London forces?

Answer 51

Yes but not stronger than hydrogen bonding

Question 52

What does Hydrogen bonding affect?

Answer 52

Hydrogen bonding affects molecules in which hydrogen is covalently bonded to either fluorine, oxygen, or nitrogen – all highly electronegative elements

Question 53

How does hydrogen bonding occur?

Answer 53

The highly electronegative element attracts electrons away from the hydrogen and forms a polar bond. There is electrostatic attraction between hydrogen and the electronegative elements. The hydrogen has an extremely high charge density and forms weak bonds with the lone pair(s) of electrons on the other element

Question 54

Hydrogen bonding is the ...

Answer 54

strongest type of intermolecular force

Question 55

Explain the hydrogen bonding in oxygen

Answer 55

The oxygen has a partially negative charge as it is highly electronegative, and hence attracts the electron pair away from the hydrogen, which is therefore partially positive. Hydrogen bonds form between the oxygen atoms (and its two lone pairs) and hydrogen atoms of neighbouring molecules.

Question 56

Explain the bonding in ammonia

Answer 56

The nitrogen has a partially negative charge as it is highly electronegative, and hence attracts the electron pair away from the hydrogen, which is therefore partially positive. Hydrogen bonds form between the nitrogen atoms (and its lone pair) and hydrogen atoms of neighbouring molecules.

Question 57

Explain the bonding in hydrogen fluoride

Answer 57

The fluorine has a partially negative charge as it is highly electronegative, and hence attracts the electron pair away from the hydrogen, which is therefore partially positive. Hydrogen bonds form between the fluorine atoms (and its three lone pairs) and hydrogen atoms of neighbouring molecules.

Question 58

Why is water able to do hydrogen bonding while the other group 6 hydrides can not?

Answer 58

Oxygen is electronegative However the other group 6 hydrides do permanent dipole-permanent dipole bonding instead, however the trend from H2S to H2Te is due to London forces - the dipole becomes greater due to more electrons

Question 59

Hydrogen bonding in ice vs liquid

Answer 59

In ice, each water molecule is bonded to 4 other water molecules in a tetrahedral geometry through covalent bonding and hydrogen bonding. This leads to a relatively open hexagonal 3D structure with several holes between molecules, which therefore lead to a lower density. In liquid water however, the molecules are able to slide over each other because the particles have more kinetic energy. This leads to their being closer together, which is why ice floats in water

Question 60

Predicting the presence of hydrogen bonding in molecules

Answer 60

Hydrogen must be bonded to a small highly electronegative element There must be at least one lone pair of electrons on the highly electronegative element

Question 61

In terms of intermolecular forces describe the trends in boiling temperatures of alkanes with increasing chain length

Answer 61

chain length increases --> more total electrons and therefore a bigger ‘electron cloud’ and increase in volume around the molecule. More more likely to be a more uneven distribution of (more) electrons leading to a greater instantaneous dipole (with more partial charge). This will induce greater dipoles and therefore there will be more electrostatic attraction between molecules, leading to increasingly high boiling points for greater chain lengths.

Question 62

Explain, in terms of intermolecular forces, the effect of branching in the carbon chain on the boiling temperatures of alkanes

Answer 62

Linear molecules- higher boiling points than branched chain molecules because they are able to align themselves closer together by lying parallel to each other. Which makes the electrostatic attraction between dipoles stronger. Larger surface areas allows for more opportunity for dipoles to exist and therefore more places where molecules can be attracted to each other. Hence giving linear molecules higher boiling points

Question 63

How is volatility determined?

Answer 63

By boiling point where high boiling points denote a low volatility. Alkanes are non-polar molecules and as such can only do instantaneous dipole-induced dipole bonding. Alcohols, in addition, are able to do hydrogen bonding due to their hydroxyl group.

Question 64

Alcohols will have a higher... / lower... than alkanes of the same size

Answer 64

boiling point | viscosity

Question 65

Why is hydrogen bonding less significant amongst longer chain alcohols

Answer 65

due to the main intermolecular force acting is London dispersion due to the non-polar hydrocarbon chain

Question 66

Why does HF have the highest boiling point

Answer 66

it is able to form hydrogen bonds between molecules

Question 67

What characterises the boiling points frim HCl to HI

Answer 67

London dispersion forces. Due to the increase in electrons, greater dipoles form and there is a stronger electrostatic attraction between molecules

Question 68

What has to happen in order for a substance to be able to dissolve?

Answer 68

The solute particles must become surrounded by the solvent particles The intermolecular forces formed between the solute and solvent particles must be strong enough to overcome the forces between the solute particles and solvent particles respectively. If the enthalpy change is about 0 then the process is neither energetically favourable nor unfavourable so entropy will facilitate the process.

Question 69

What happens when an ionic compound is dissolved in water?

Answer 69

the positive ions are attracted to the partially negative oxygen atoms and the negative ions are attracted to the partially positive hydrogen atoms.

Question 70

What happens during the hydration stage when an ionic compound dissolved in water

Answer 70

the ions are pulled out of their giant ionic lattice and surrounded by water molecules The ionic bonds in the lattice are therefore broken as well as the hydrogen bonds between water molecules. This is an endothermic process and requires energy. o New hydrogen bonds are formed between the ions and water molecules. This is an exothermic process and gives out energy.

Question 71

What happens to NaCl so dissolution can occur

Answer 71

The total enthalpy change is 0, however is still positive (exothermic/ unfavourable), so dissolution occurs because of entropy.

Question 72

Why is Al2O3 insoluble

Answer 72

It has strong ionic bonds due to Al3+'s high charge density. | Entropy is not strong enough to drive the process

Question 73

What are the factors that influence the choice of solvents in terms of hydrogen bonding

Answer 73

Alcohols are polar substances due to their hydroxyl groups Hydrogen bonds between the water molecules and the alcohol molecules break and new hydrogen bonds form between the water and alcohol molecules collectively. For longer alcohol molecules, the hydrogen bonding is 'diluted' by the instantaneous dipole-induced dipole bonding performed by the carbon chain, hence the longer the carbon chain, the less soluble an alcohol will be

Question 74

Why are halogenoalkanes insoluble

Answer 74

The strongest intermolecular force between halogenoalkane molecules is permanent dipole-permanent dipole bonding. Therefore hydrogen bonding can't be formed. The hydrogen bonding in water is stronger than the permanent dipole-permanent dipole bonding that would form between water and halogenoalkanes, hence they are insoluble. And entropy isn't enough to make this process favourable because it's too endothermic.

Question 75

What does non aqueous mean

Answer 75

refers to any solvent that is not water

Question 76

Why are cyclohexanes and heptanes often used?

Answer 76

'like dissolves like' Non polar molecules- the strongest intermolecular forces present are instantaneous dipole-induced dipole bonding so non-polar substances will usually dissolve readily in each other.

Question 77

What is metallic bonding?

Answer 77

Metallic bonding occurs between metals only. The metal atoms lose their outer electrons, which become delocalised and they themselves become positive metal ions.

Question 78

How are giant metallic lattices held together?

Answer 78

The giant metallic lattice is held together by the strong electrostatic attraction between the positive metal ions and the delocalised (negative) sea of electrons.