Topic 4: Chemical Bonding and Structure

Question 1

Ionic vs covalent

Answer 1

Both two main classes of compounds
Ionic: NM + M
Covalent: NM + NM

Elements far away from each other tend to form ionic bonds
Elements close together tend to form covalent bonds

Question 2

How are positive and negative ions usually formed?

Answer 2

Positive ions are usually formed by metallic elements by the loss of valence electrons.
Ex. Mg - 2e- = Mg2+

Negative ions are usually formed by non metallic elements by the gain of electrons
Ex. O+2e- = O2-

Question 3

Why do elements in the main groups of the periodic table (group 1, 2, 13 (to a certain extent), 15, 16, 17) form ions?

Answer 3

Electrons gained or lost electrons configuration of the nearest noble gas. That is, electrons are gained or lost to make an ion that is isoelectronic (same number of electrons) with the nearest noble gas.

Another way of saying: To achieve full outer shell of electrons.

Question 4

Common ions to remember:
NH4+
OH-
O2-
NO3-
HCO3 2-
CO3 2-
SO4 2-
PO4 3-

Answer 4

Ammonium
Hydroxide
Oxide
Nitrate
Hydrogen carbonate
Carbonate
Sulfate
Phosphate

Question 5

What in the periodic table can form more than one ion?

Answer 5

Transition metals
ex. Iron an form iron(II), Fe2+, and iron (III), Fe3+

Question 6

What determines the number of electrons lost or gained?

Answer 6

The electron configuration of an atom

Question 7

Electrons cannot be created or destroyed, therefore…

Answer 7

The total number of electrons lost must also equal the total number gained.

Question 8

What is an ionic bond?

Answer 8

An ionic bond is an electrostatic attraction between oppositely charged ions

Question 9

what is an electrostatic attraction?

Answer 9

Attraction between oppositely charged ions

Question 10

What holds a crystal of sodium chloride together?

Answer 10

Sodium chloride consists of a giant lattice of NA+ and CL- ions. The electrostatic attraction between the oppositely charged ions hold crystals together. These electrostatic forces are so strong, so it is difficult to break apart the lattice structure.

Question 11

Do ionic compounds have high or low melting and boiling points?

Answer 11

Ionic compounds usually have high melting point and boiling points. This means that ionic substances are usually solids at room temperature.

Question 12

Why do ionic compounds have high melting and boiling points?

Answer 12

It is due to the strong electrostatic forces between the oppositely charged ions. When an ionic solid is melted, the electrostatic forces throughout the giant lattice must be broken, because they are so strong, a lot of energy is required.

Question 13

Why does magnesium oxide has a much higher melting point than sodium chloride?

Answer 13

Because the electrostatic attraction between the 2+2 minus ions in magnesium oxide lattice are much stronger than those between the 1+ and 1- ions in sodium chloride.

Question 14

What are examples of physical properties?

Answer 14

Examples include melting boiling point, solubility, electrical conductivity, etc. Chemical properties are how substances reacts.

Question 15

What is meant by volatility and how is it for ionic solids?

Answer 15

Volatility refers to how readily a substance evaporates. Ionic solids have low lower volatility because the electrostatic forces between the ions are strong.

Question 16

Can ionic substances conduct electricity?
Solid and liquid

Answer 16

Ionic substances do not conduct electricity when solid. In the solid-state, the ions are held tightly in position in the lattice structure so that they are not free to move around (other than vibrate).

When an ionic substance is melted the isles were able to move freely throughout the liquid. Positive ions can move towards a negative electrode and negative ions towards a positive electrode so allowing the conduction of electricity.

Question 17

What is ionic compound solubility in water?

Answer 17

Ionic substances are often soluble in water. Water is a polar solvent, and energy is released when the ions are hydrated by being surrounded (ion-dipole attractions) by water molecule. This energy pays back the energy required to break apart the ionic lattice.

Question 18

What is the electrical conductivity in ionic solutions?

Answer 18

Aqueous solutions (solutions made with water) Ionic substances conduct electricity. This is because the ions are free to move around.

Question 19

Are ionic solids soluble in non-polar solvents? Why?

Answer 19

Ionic solids are not usually soluble in non-polar solvent such as hexane. This is because a great deal of energy is required to break apart the ionic lattice and this is not paid back by the energy released when the non-polar solvent form interaction with the ions (London forces).

Question 20

Where is the electrostatic attraction between covalent bonds?

Answer 20

There’s electrostatic attraction between a shared pair of electrons and the nuclei of the atom that are bonded

Question 21

What are the pairs of electrons in outer shell of atoms that are not involved in covalent bonds called?

Answer 21

Lone pairs

Question 22

What holds atoms together in a covalent bond?

Answer 22

The covalent bond is the electrostatic attraction between positively charged nuclei of both atoms and the shared power of electrons.

Question 23

why are triple bonds shorter than double bonds which are shorter than single bonds?

Answer 23

Because there is a stronger attraction between the bonding electrons and the nuclei when there are more electrons in a bond.

Question 24

What happens to the bond length and energy as it goes down the periodic table?

Answer 24

The bond between the elements get weaker as a bond gets longer. This is because, that the atoms get bigger, the electron pair and a covalent bond is further away from the nuclei of the atom making up the bond. The electron pairs further away from the nuclei, it is less strongly attracted and a covalent bond is weaker.

Question 25

What are the most electronegative elements in the periodic table?

Answer 25

Nitrogen, oxygen, fluorine, chlorine

Question 26

What are molecules called when the atoms attract electron pair unequally in a covalent bond?

Answer 26

Polar molecules

Question 27

What determines the polarity of a molecule?

Answer 27

The difference in electronegativity of the atoms.

Question 28

What is electornegativity a measure of?

Answer 28

of the attraction of an atom in a molecule for the electorn pair in the covalent bond of which it is a part

Question 29

what determines how strongly the electrons are attracted?

Answer 29

Depends on the size of the individual atoms and the nuclear charge

Question 30

What does it mean when the fluorine is more electronegative than hydrogen in HF?

Answer 30

It means that fluorine attracts electrons in the H-F bond more strongly than a hydrogen atom does. The electrons in a bond like closer to the fluorine down to the hydrogen.

Question 31

Why don't noble gases have electronegativity values?

Answer 31

Because they do not form compounds

Question 32

Which has higher electronegativities: non-metals or metals?

Answer 32

non-metals

Question 33

What's the trend in electronegativity in the periodic table?

Answer 33

Electronegativity generally decreases down a group and increases across a period

Question 34

What's the pattern between electronegativity with covalent and ionic bonds?

Answer 34

Atoms with **similar electronegativities** will form **covalent bonds**. Atoms with **widely different electronegativities** will form **ionic bonds**. The difference in electronegativity can be taken as a guide to how ironic or how covalent bond between two atoms as likely to be.

Question 35

Do nonmetals have a higher or lower electronegative than metals?

Answer 35

Nonmetals have a higher electronegativity than metals

Question 36

What value of electronegativity represent a covalent and ionic bond?

Answer 36

If the difference more than 1.7, the bonding between two elements is ironic. If the difference is less than 1.7, the bonding between two elements is covalent.

Question 37

What is the difference between electrostatic attraction and electronegativity?

Answer 37

Electrostatic attraction is the force between two oppositely charged ions and electronegativity is the ability to attract electrons to an atom.

Question 38

What is the octet rule?

Answer 38

The concept that atoms and covalent bonds have a tendency to have a full valence shell of a total of eight electrons.

Question 39

What is a coordinate covalent bond or dative covalent bond?

Answer 39

They coordinate covalent bond is a type of covalent bond in which both electron come from the same atom. Once a coordinate covalent bond has been formed, it is identical to an ordinary covalent bond.

Question 40

explain the dative covalent bond in NH4+

Answer 40

H+ does not have any electrons with which to form a covalent bond, but NH3 has a long pair of electrons that can be used to form a covalent bond.

Question 41

What is the bond situation in carbon monoxide?

Answer 41

Both atoms can attain an octet if the oxyen atom donates a pair of electrons to carbon in the formation of a coordinate covalent bond there is now a triple bond between the two atoms, made up of two 'ordinary' covalent bonds and one coordinate covalent bond. both atoms have a lone pair of electrons

Question 42

What is it called when two molecules are bonded together?

Answer 42

An adduct

Question 43

What is meant by resonance structure

Answer 43

Individual structures that differ only in the position of the double bond

Question 44

How to determine central atom in lewis structure?

Answer 44

Usually it is the element with only one atom, or its the least electronegative atom

Question 45

What is simliar about O3 and NO2-?

Answer 45

they are isoelectronic and has the same lewis stucture

Question 46

How are NO2+ and CO2 isoelectronic?

Answer 46

same lewis structure

Question 47

What does the valence shell electron pair repulsion (VSEPR) theory tell us?

Answer 47

It allows us to predict the shapes of molecules

Question 48

What is the VSEPR theory?

Answer 48

Pairs of electrons in the valence shell of an atom repel each other and will therefore take up positions in space to minimize these repulsion – to be as far apart in space as possible. Can be bonding pairs or non-bonding pairs (lone pairs)

Question 49

What does the shape of a molecule depend on?

Answer 49

It depends on the number of electron pairs in the outer shell of the central atom.

Question 50

Why do we use electron domains instead of number of bonds?

Answer 50

Because a double or triple bond behaves as if it were just one electron pair.

Question 51

Why does a multiple bond count as a single electron pair?

Answer 51

Because the electrons are constrained to occupy the same region of space

Question 52

What is the shape and bond angle of molecules with 2, 3, 4 electron domains?

Answer 52

2: Linear and 180˚ 3: Trigonal planar and 120˚ 4: Tetrahedral and 109.5˚

Question 53

Basic and actual shapes of some specific molecules

Answer 53

Question 54

What is the angle of bent and trigonal pyramidal?

Answer 54

Bent: 105˚ if two lone pairs 117˚ if one Trigonal pyramidal: 107˚

Question 55

Do lone pairs contribute to overal shape?

Answer 55

Yes, it just cannot be seen

Question 56

What is the order of repulsion strength for pairs of electrons? and Why

Answer 56

lone pairs-lone pairs > lone pairs-bonding pair > bonding pair-bonding pair Because the lone pairs are held closer to the central nucleus than are bonding pairs. (Long pairs are in the outer shell of the central atom, whereas bonding pair can be imagined as being, on average, halfway between the bonded atoms.

Question 57

What does the presence of long pairs result in bond angles?

Answer 57

lone pairs repel bonding pairs of electrons more than the bonding pairs repel each other therefore the presence of lone pairs result in a closing up of bond angles.

Question 58

Why do we call some bonds polar?

Answer 58

Because the electronegativity difference between two atoms covalently bonded together results in the electrons lying more towards one atom than the other. For a molecule to be polar and must have a positive and a molecule and a negative end.

Question 59

How can some individual bonds be polar but a molecule is non-polar?

Answer 59

Because of the symmetry of the molecule, the dipole moment of the individual bonds canceled out.

Question 60

Why is CCl4 for non-polar？

Answer 60

Although each individual bond is polar due to the difference in electronegativity of the atoms, because of the symmetry of the molecule, the dipoles cancel.

Question 61

What are allotropes of carbon?

Answer 61

Different forms of the same element. Diamond, graphite, graphene and fullerenes are all allotropes of carbon. They all contain only carbon atoms, but these atoms are joined together differently in each structure.

Question 62

What is the structure of diamond and graphite and how do they differ? (structure, shape, bonds)

Answer 62

Diamond and graphite has a giant covalent (macromolecular) structure. Diamond: There are no individual molecules – the whole structure, continuing in 3 dimensions, represents one giant molecule. Each carbon atom is drawn to for others, in a tetrahedral array, by covalent bonds. Graphite: it has a layer structure. Each C is covalently bonded to three other layers in a trigonal planner array. There are covalent bonds between the C atoms within a layer but only London forces between the layers. The presence of weak forces between the layers is usually given as the explanation that graphite is a good lubricant.

Question 63

What are the properties of diamond? (MP/BP, conductivity, solubility)

Answer 63

Diamond has a very high melting and boiling point because a lot of energy must be supplied to break covalent bonds. Has the highest thermal conductivity. Diamond is very hard for the same reason. Diamond is the hardest naturally occurring substance. Diamond does not conduct electricity because all electrons are held strongly in covalent bonds and are therefore not free to move around in the structure. Diamond is not soluble in water or organic solvents because the forces between the atoms are too strong. The energy to break these covalent bonds would not be paid back on the C atoms were solvated.

Question 64

What are the properties of graphite? (MP/BP, bonds, conductivity,

Answer 64

Graphite has a very high melting/boiling point because covalent bonds within the layers must be broken when it is melted/boiled. Because of the strong covalent bonds between atoms, graphite is not soluble in water or non-polar solvents. Graphite conduct electricity because each C atom forms only 3 covalent bonds - the extra electrons not used in these bonds are able to move within layers. The free electron is called delocalized electron.

Question 65

What are substances of giant structures called?

Answer 65

Network solids

Question 66

What are the properties of graphene? (Structure, strength, MP/BP, bonds, heat and electrical conductivity)

Answer 66

Graphing consists of a single layer of graphite. Only very small pieces happen forms so far. It has a very high tensile strength and would be expected to have a very high melting point because covalent bonds need to be broken to break the sheet. It is a very good electrical and thermal conductor through to the delocalised electron from C only forming 3 bonds.

Question 67

What are the properties of C60 fullerene (buckminsterfullerene)? (structure, bonds, solubility, conductivity)

Answer 67

It is considered a molecular rather than a giant structure. It consists of individual C60 molecules, with covalent bonds within the molecule and London forces between the molecules. C60 is insoluble in water but soluble in some organic solvents such as benzene. The energy to overcome the London forces between the C60 molecules is paid back by the energy released when London forces are formed between the C60 molecules and the solvent. C60 does not conduct electricity. Although each C forms 3 bonds in the C60 molecule, so that there is delocalisation of electricity over the molecule, the molecular structure means that electrons are not able to move from one molecule to the next.

Question 68

Properties of silicon dioxide?

Answer 68

SiO2 has a giant covalent structure. Silicone atom is bonded to 4 oxygen atoms in a tetrahedral array. Each oxygen is bonded to two silicon atoms. Due to the two lone pairs on each oxygen atom, the basic shape about each Si-O-Si unit is bent. The oxide has high melting and boiling points, how is covalent bonds between atoms must be broken in order to melt/boil it and it requires a lot of energy.

Question 69

Diamond vs graphite vs fullerene boiling and melting point.

Answer 69

Diamond and graphite are giant structures but fullerene is a molecular structure. Diamond and graphite must break covalent bond to be melted Fullerene only breaks intermolecular forces (London forces) when melted. Covalent bonds are must stronger than intermolecular forces, therefore more energy is required for diamond and graphite to melt.

Question 70

What's the difference between intramolecular forces and intermolecular forces?

Answer 70

Intramolecular forces are forces within a molecule (covalent, ionic, metallic bonding) Intermolecular forces are forces between molecules (Van der Waals' forces)

Question 71

Which one is stronger: intermolecular forces or covalent bonds

Answer 71

Covalent bonds are much stronger than intermolecular forces

Question 72

Where can you find London forces? And where does it come from?

Answer 72

London forces are present between all molecules in a solid and liquid states. It is found between non-polar atoms/molecules. London forces or temporary instantaneous dipoles–induced dipole interactions because electrons in an atom are in constant motion and at any one time they will not be symmetrically distributed about the nucleus. This results in a temporary instantaneous dipoles in the atom which will induce an opposite dipole in a neighbouring atom. These tables will attract each other so that there's an attractive force between atoms.

Question 73

What are the Van der Waals' forces?

Answer 73

Van der Waals' forces is the collective name given to the forces between molecules and includes London (dispersion) forces, dipole-dipole interactions and dipole–induced dipole interactions.

Question 74

How does the strength of London forces increase?

Answer 74

In general, London forces get stronger as a relative molecular mass increases or the number of electrons in molecules increase.

Question 75

What forces are present in polar molecules?

Answer 75

London dispersion and dipole dipole forces

Question 76

What do dipole dipole forces due to polar molecules?

Answer 76

They cause melting point and boiling points to be higher

Question 77

What's the difference between polar vs nonpolar molecules with similar relative molecular mass?

Answer 77

Polar molecules have higher melting and boiling points and non-polar molecules

Question 78

Why does Br, a non-polar molecules, have a higher boiling point than some other polar molecules?

Answer 78

The highest boiling point as a result of its highest relative molecular mass and therefore strongest London force

Question 79

why is H2O then what would be expected from a relative molecular mass?

Answer 79

Just suggest that there must be intermolecular forces other than London forces between H2O molecules and these intermolecular forces are stronger than the London forces. This intermolecular force is called a hydrogen bond

Question 80

Which is stronger hydrogen bonding or covalent bonding?

Answer 80

Hydrogen bonding is the strongest of the intermolecular forces but it is still much weaker than covalent bonding.

Question 81

When does hydrogen bonding occur? How can you tell?

Answer 81

Hydrogen bonding occurs between molecules when a very electronegative atom, N, O, F, is joined to a hydrogen atom in the molecule. As long as there's N, O, F atom in a molecule there will be hydrogen bonding.

Question 82

What happens to the bonds when melted or boiled?

Answer 82

Only intermolecular forces are broken when covalent molecular substances are boiled – covalent bonds are not broken.

Question 83

What is the weakest to strongest intermolecular forces and why it causes differences in melting and boiling points?

Answer 83

London < permanent dipole – dipole < hydrogen bonding The stronger the intermolecular force the more energy must be supplied to break them and a higher boiling point.

Question 84

What type of intermolecular forces are in substances containing H bonded to N, O or F.

Answer 84

Hydrogen bonding, permanent dipole – dipole, London forces

Question 85

What intermolecular forces are found in polar substances?

Answer 85

Permanent dipole – dipole, London forces

Question 86

What intermolecular forces are found in non-polar substances?

Answer 86

London forces

Question 87

How does relative molecular mass influence melting and boiling points?

Answer 87

Generally substances with higher relative molecular masses have higher melting point and boiling points due a stronger London forces.

Question 88

What does 'like dissolves like' means?

Answer 88

Generally a substance will dissolve in a solvent if the intermolecular forces in the solute and solvent are similar

Question 89

What determines if a substance dissolves or not?

Answer 89

It depends (in part) on how much energy is needed to overcome intermolecular forces in the solvent and solute and then how much energy is released, to pay back the energy, when intermolecular forces are formed between solvent and solute molecules in the solution.

Question 90

What are substances with hydrogen bonding solubility in water?

Answer 90

Participate in hydrogen bonding will generally be soluble in water, because they're able to hydrogen bonds with water.

Question 91

Why can pentane dissolve in hexane but pentane cant dissolve in water?

Answer 91

Because pentane and hexane both have London forces between them but pentane does not dissolve in water because only London forces would before between pentane and water molecules

Question 92

Why is ethanol soluble in water?

Answer 92

It is very soluble in water, able to hydrogen bond to the water. The hydrogen bonding between water molecules and ethanol molecules in the solution releases energy and pays back the energy to break up hydrogen bonds in pure water and pure ethanol.

Question 93

Why are longer chain alcohol less soluble in water?

Answer 93

Although there is some hydrogen bonding between the O–H group of the alcohol and water molecules, the long hydrocarbon chain prevents water molecules on either side from hydrogen bonding to each other. Energy is needed to break the hydrogen bonds between water molecules, but this is not paid back as only London forces form between water molecules and the hydrocarbon part of the molecule

Question 94

How does ionic substances dissolve in polar solvents?

Answer 94

Aqueous solutions contain aqueous ions. Ion – dipole interactions formed between the water and the ions. Energy is required to overcome the electrostatic forces in the ionic lattice but energy is released when hydrated ions are formed. If the energy released when the hydrated ions are formed is comparable to the energy required to break apart an ionic lattice then the substance is generally soluble.

Question 95

Are ionic substances usually soluble in non-polar solvents?

Answer 95

They are not usually soluble because the interaction between ions and a non-polar solvents would be weak London forces.

Question 96

What is meant by a delocalized electrons?

Answer 96

If you look lies electron do not belong to anyone metal atom but rather are able to move throughout the structure.

Question 97

Comparison of the physcial properties of ionic and covalent molecular substances?

Answer 97

Question 98

What is metallic bonding?

Answer 98

A metallic bond is the electrostatic attraction between the positive ions in the lattice and the delocalised electrons.

Question 99

What determines the strength of a metallic bond?

Answer 99

The strength is determined by the number of the look like electrons, the charge on the cation, and the radius of the cation

Question 100

What is the trend in radius on the periodic table?

Answer 100

Radius get smaller across, due to the number of protons in the nucleus, they become stronger and pulls more electrons towards the nucleus. The radius increases as it goes down the periodic table since there are more shells

Question 101

Describe a metallic structure?

Answer 101

Metals contain a regular lattice arrangement of positive ions surrounded by a 'sea' of delocalized electrons

Question 102

Suggest reasons why magnesium has a higher melting point than sodium

Answer 102

1) Mg forms a 2+ ion compared with Na, which forms a 1+ ion. This means that the electrostatic attraction between ions and delocalized electrons is stronger in magnesium 2) magnesium ion is smaller than the sodium ion, because the delocalised electrons are closer to the nucleus of the positive ion in Mg and are more strongly attracted. 3) There are 2 delocalized electrons per atom in magnesium. Therefore there will be a stronger electrostatic attraction between ions and the delocalized electrons.

Question 103

Define lustrous

Answer 103

Shiny, when freshly scratched/cut

Question 104

Define ductile

Answer 104

Ability to be drawn out in a thin wire

Question 105

Define malleable

Answer 105

May be hammered into shape – many uses arise from the ability to easily sheet metal e.g. making car bodies

Question 106

How do metals conduct electricity?

Answer 106

Because the delocalized electrons are free to move around

Question 107

Why are metals malleable/ductile?

Answer 107

Because of the non-– directionality of the bonding. The metal ions in the lattice attract the delocalized electrons in all directions. So when two layers slide over each other, the bonding in the resulting structure it's exactly the same as in the original.

Question 108

How do metals do compared to ionic solids in malleability?

Answer 108

Metals are malleable as the resulting structure is the same as the original but ionic solids are brittle and the placement of one layer relative to the other results in like charges repelling each other causing them to fall apart.

Question 109

Define alloys

Answer 109

Alloys are homogenous mixtures of two or more metals, or of a metal with a nonmetal

Question 110

Why do alloys tend to be stronger and stiffer than pure metals?

Answer 110

The introduction of a larger atom makes it more difficult for the planes of atom/ions to slide over each other