Topic 2 Chemical bonding and structure

Question 1

State the physical properties of metals

Answer 1

• high melting temperatures
• good electrical conductivity
• good thermal conductivity
• malleability
• ductility

Question 2

What is mainly responsibly for the characteristic properties of metals?

Answer 2

delocalised electrons

Question 3

Define delocalised electrons

Answer 3

electrons that aren’t associated with any single atom or any single covalent bond

Question 4

What is metallic bonding?

Answer 4

the electrostatic force of attraction between the nuclei of metal cations and delocalised electrons

Question 5

Why do metals have high melting temperatures?

Answer 5

metals have a giant lattice structure so lots of electrostatic attractions need to be overcome

Question 6

What determines the melting temperatures of a metal?

Answer 6

• the number of delocalised electrons per cation e.g. Group 1 metals have a lower melting temp than Group 2
• size of the cation e.g. smaller cations are closer to the delocalised electrons and greater force of attraction

Question 7

Why can metals conduct electricity?

Answer 7

when a potential difference is applied across the ends of the metal, the delocalised electrons are attracted to and move towards the positive terminal

Question 8

Why are metals good thermal conductors?

Answer 8

1. Free-moving delocalised electrons pass kinetic energy along the metal
2. cations are closely packed together and pass kinetic energy from one cation to the other

Question 9

Why are metals ductile/malleable?

Answer 9

delocalised electrons can move throughout the metal structure

Question 10

Define ionic bonding

Answer 10

the strong electrostatic attraction between oppositely charge ions

Question 11

How do you determine the strength of ionic bonding?

Answer 11

by calculating the amount of energy required in one mole of solid to separate the ions to infinity so they can no longer interact

Question 12

What are the factors that determine the strength of ionic bonding

Answer 12

• the smaller the ions, the more energy required (for ions of the same charge)
• higher ionic charge, increased strength

Question 13

Name the physical properties of ionic compounds

Answer 13

• high melting temperatures
• brittleness
• poor electrical conductivity when solid but good when molten
• often soluble in water

Question 14

Why do ionic compounds have high melting temperatures?

Answer 14

-consist of a giant lattice with lots of oppositely charged ions so combined electrostatic forces is large and requires large amounts of energy

Question 15

Why do ionic compounds have poor electrical conductivity (when solid)?

Answer 15

• no delocalised electrons
• ions aren’t free to move when potential difference is applied
• molten will conduct as ions are mobile
• solid lithium nitride will conduct electricity
• aqueous ionic solutions conduct electricity

Question 16

What is the most convincing evidence for the existence of ions?

Answer 16

the ability of an ionic compund to conduct electricity and undergo electricity when moleten or in aqueous solution

Question 17

Define a covalent bond

Answer 17

a covalent bond is formed when 2 atoms share 1 or more pairs of electrons

Question 18

What are the 2 types of overlap in a covalent bond?

Answer 18

sigma and pi bonds

end on end overlap and sideways overlap

Question 19

Define bond length

Answer 19

the distance between nuclei of the 2 atoms that are covalently bonded together

Question 20

What is electronegativity?

Answer 20

the ability of an atom to attract a bonding pair of electrons

Question 21

Describe the trends of electronegatvity

Answer 21

• decreases down a group

- increases from left to right across a period

Question 22

What is a polar covalent bond?

Answer 22

a type of covalent bond between 2 atoms where the bonding electrons are unequally distributed, because of this, one atom carries a slightly positive charge and the other a slightly negative charge

Question 23

What is a discrete simple molecule?

Answer 23

an electrically neutral group of 2 or more atoms held togther by chemical bonds

Question 24

What is a displayed formula?

Answer 24

shows each bonding pair as a line drawn between the two atoms involved

Question 25

Whta is a dative covalent bond?

Answer 25

formed when an empty orbital of one atoms overlaps with an orbital containing a non-bonding/lone pair of electrons of another atom

Question 26

Give examples where dative covalent bonds occur

Answer 26

• hydroxonium ion, H3O+

- aluminium chloride, Al2Cl6

Question 27

What is the electron pair repulsion theory?

Answer 27

• the shape of a molecule or ion is caused by repulsion between the pairs of electrons surrounding the central atom (both bond pairs and lone pairs)
• the elctron pairs arrange themselves around the central atom so that repulsion between them is minimal
• lone pair-lone pair repulsion > lone pair-bond pair repulsion > bond pair-bond pair repulsion

Question 28

What shape consists of 2 bond pairs?

Answer 28

linear e.g. BeCl2, CO2(each double bond treated as an electron pair)

Question 29

What shape consists of 3 bond pairs?

Answer 29

trigonal planar e.g. BCl3

Question 30

What shape consists of 4 bond pairs?

Answer 30

tetrahedral e.g. CH4

Question 31

What shape consists of 5 bond pairs?

Answer 31

trigonal bipyramidal e.g. PCl5

Question 32

What shape consists of 6 bond pairs?

Answer 32

octahedral e.g. SF6

Question 33

What shape consists of 3 bond pairs and 1 lone pair?

Answer 33

trigonal pyramidal e.g. NH3

Question 34

What shapes consists of 2 bond pairs and 2 lone pairs?

Answer 34

v-shaped e.g. H2O

Question 35

Bond angle for linear shape e.g. BeCl2

Answer 35

180 degrees

Question 36

Bond angle for trigonal planar shape e.g. BCl3

Answer 36

120 degrees

Question 37

Bond angle for tetrahedral shape e.g. CH4

Answer 37

109.5 degrees

Question 38

Bond angle for trigonal pyramidal NH3

Answer 38

107 degrees

Question 39

Bond angle for v-shaped e.g. H2O

Answer 39

104.5 degrees

Question 40

Bond angle for octahedral e.g. SF6

Answer 40

90 and 180 degrees

Question 41

Why are ionic compounds brittle?

Answer 41

• layers of ions slide over one another when stress is applied
• ions of same charge are next to each other and repel one another which breaks crystal apart

Question 42

Why are ionic compounds soluble in water?

Answer 42

-positive and negative ions both attracted to water molecules due to polarity that water possesses

Question 43

What’s a dipole?

Answer 43

exists when 2 charges of equal magnitude but opposite signs are separated by a small distance

Question 44

Define a hydrogen bond

Answer 44

an intermolecular interaction between a hydrogen atom of a molecule bonded to an atom which is more electronegative than hydrogen and another atom in the same or a different molecule

Question 45

How do London forces occur?

Answer 45

• the electron density of a non-polar molecule fluctuates due to kinetic energy
• this causes an induced dipole in the next molecule which causes a London force

Question 46

When does the force of a London force increase?

Answer 46

• when there are more electrons in the molecule, it causes there to be greater fluctuations in electron density so the induced dipoles and instantaneous dipoles are larger
• more points of contact, the larger the London forces e.g. shape and size of molecules

Question 47

When are London forces present?

Answer 47

in every molecule- permanent dipole or not

Question 48

When are permanent dipoles present?

Answer 48

if the molecule is polar- the electronegativities -differ

Question 49

When does hydrogen bonding occur?

Answer 49

when the atom bonded to hydrogen is more electronegative than hydrogen, mainly with oxygen, nitrogen or fluorine