COVALENT AND METALLIC BONDING

Question 1

define covalent bond

Answer 1

a covalent bond is the bond formed by sharing of electrons between 2 atoms

Question 2

explain the formation of H2(bonds)

Answer 2

H2 is formed by a single covalent bond b/w the 2 hydrogen atoms.

• each hydrogen atom has 1 valence electron in its outermost shell.
• it needs one more electron to attain the stable duplet electronic configuration.
• a pair of electrons is shared between the 2 hydrogen atoms
• a single covalent bond is formed and both hydrogen atoms have attained the stable noble gas configuration

Question 3

explain the bond in O2

Answer 3

O2 is formed by double covalent bonds between 2 oxygen atoms

• each oxygen atom has 6 valence electrons in its outermost shell.
  it needs 2 more electrons to attain the noble gas configuration.
• thus 2 pairs of electrons are shared between the oxygen atoms
• a double covalent bond is formed, and each oxygen atom has attained the noble gas configuration

Question 4

explain the bonds in N2

Answer 4

N2 is formed by triple covalent bonds between the 2 nitrogen atoms
- each nitrogen atom has 5 valence electrons in its outermost shell
it needs 3 more electrons to achieve the noble gas configuration
thus 3 pairs of electrons are shared between the 2 nitrogen atoms
- a triple covalent bond is formed
- each nitrogen atom has achieved the stable noble gas configuration

Question 5

describe the formation of bonds in H2O

Answer 5

1. the oxygen atom shares 2 valence electrons with the 2 hydrogen atoms
2. each hydrogen atom shares its 1 valence electron with the oxygen atom
3. oxygen atom achieves the stable octet electronic configuration
4. each hydrogen atom achieves the stable duplet electronic configuration
5. the sharing of 4 electrons between oxygen atom and 2 hydrogen atoms, results in the formation of 2 single covalent bonds

Question 6

describe the formation of bonds in CO2
- draw dot ad cross first

Answer 6

1. the carbon atom shares its 4 valence electrons with the 2 oxygen atoms .
2. each oxygen atom shares its 2 valence electrons with the carbon atom
3. both carbon and the 2 oxygen atoms attain the stable octet electronic configuration
4. the sharing of 8 electrons results in the formation of 2 double covalent bonds in the CO2 molecule

Question 7

describe the formation of bonds COCl2
- draw dot and cross diagram first

Answer 7

1. the carbon atom shares its 4 valence electrons with 2 chlorine and one oxygen atom
2. the oxygen atom shares 2 valence electrons with the carbon atom
3. each chlorine atom shares 1 valence electron with the carbon atom
4. resulting in the carbon, oxygen and 2 chlorine atoms in achieving the stable octet electronic configuration
5. by the sharing of 2 electrons, a single covalent bond is formed between both chlorine and carbon atom
6. by sharing 4 valence electrons, a double covalent bond is formed between the carbon and oxygen atom.

Question 8

describe the bonding and structure of simple molecular structure

atoms are molecules

Answer 8

• atoms are held together by strong covalent bonds
• molecules are held together by weak intermolecualr forces of attraction

- it has covalent bonding

Question 9

physical properties of simple molecular substance (3)

Answer 9

• low mp/bp
• insoluble in H2O, soluble in organic solvents (except alcohol)
• don’t conduct electricity (except HCl, SO2, NH3 when dissolved in water)

Question 10

why do simple molecular substances have low mp/bp?

Answer 10

a little amount of energy is needed to overcome the weak intermolecular forces of attraction between the molecules

- thus gas/volatile liquid at rtp mostly

Question 11

why don’t simple molecular substances conduct electricity in any state?
Why do NH3,HCl,SO2 conduct electricity when dissolved in water?

Answer 11

• simple molcular substances do not have mobile ions or electrons to conduct electricity
• HCl,SO2,NH3 when dissolved in water have form ions, that carry the charge and conduct electricity

Question 12

define a giant molecular structure

Answer 12

a giant molecular structure is a structure that is made up of a giant network of atoms that are covalently bonded

Question 13

3 physical properties of giant molecular structure

Answer 13

1. high mp/bp
2. insoluble in H2O and organic solvents
3. dont conduct electricity(except graphite)

Question 14

why do giant molecular structure has high mp/bp?

Answer 14

giant molecular structure are made up of a giant network of atoms that are held together by strong covalent bonds.
it is very difficult to break these bonds
thus a large amount of energy is required to overcome the strong covalent bonds

Question 15

why are giant molecular structure insoluble in H2O and organic solvents?

Answer 15

the atoms in giant molecular structure are held together by very strong covalent bonds.
the solvent molecules are not strong enough to break these strong covalent bonds

Question 16

why don’t giant molecular structure conduct electricity ?

Answer 16

the outer most electrons in the giant molecular structures are used for making bonds
thus there are no mobile electrons to move freely throughout the structure and conduct electricity

except grahite

Question 17

list and explain the properties of diamond

2 of them

Answer 17

1. hard and has high mp/bp
   - each carbon atom of diamond, is covalently bonded to 4 other carbon atoms to form a three-dimenionsal structure.
   - a lot of energy is required to overcome the strong covalent bonds
2. cannot conduct electricity
   - all the valence electrons are used for making covalent bonds
   - there are no mobile electrons to move freely throughout the structure and conduct electricity

Question 18

structure of graphite and its accountance for its physical properties

Answer 18

1. graphite is a allotrope of carbon
2. each carbon atom is covalently bonded to 3 other carbon atoms
   - this form a continuous layer of hexagons

high mp/bp
- a lot of energy is needed to break the strong covalent bonds between the carbon atoms

soft and slippery
each carbon atom layer is held together by weak intermolecular forces of attraction
its easy for one layer to slide over another when force is applied

conduct electricty
- each carbon atom has 1 free valence electron not used for bonding
- this electron can move freely through graphite and conduct electricty

this electron is said to be delocalised( doesn’t belong to any carbon)

Question 19

structure of silicon dioxide and its physical properties

Answer 19

high mp/bp
- each silicon atom is covalently bonded to 4 oxygen atom. each oxygen atom is covalently bonded to 2 silicon atom. this forms a three-dimensional structuree
- the strong covalent bonds are difficult to break

doesn not conduct electricty
- no mobile electrons to conduct electricity

• similar structure as that of diamond

Question 20

define metallic bonding

Answer 20

metalic bonding refers to the forces of attraction between positively charged ions and “sea of mobile electrons”

Question 21

explain structure of metals.

how is it positive metal ions surrounded by ‘sea of mobile electrons’

Answer 21

1. in a metal lattice, metal atoms lose their outermost electrons, to form positively charged ions
2. the outer electrons no longer belong to any metal atom and are said to be delocalised.
3. the outer electrons move freely between the metal ions like a cloud of negative charge
4. hence the metal structure is described as a lattice of positive ions surrounded by a ‘sea of mobile elctrons’

Question 22

list and explain 4 properties of metals

Answer 22

1. good conductors of electricity
   - outer electrons are free to move within the metal lattice.
   - mobile electrons carry charge, allowing metal to conduct electricity

good conductors of heat
- movement of mobile electrons within the metal lattice allows heat energy to be transffered easily.

high density , mp, bp
- atoms are packed tightly close together and held together by strong metallic bonds
- a large amount of energy is needed to break these bonds.

malleable and ductile’
malleable:- hammered into different shapes
ductile:- drawn into thin wires without breaking

before a force is applied, the metal atoms form an orderly and rigid arrangement
when a force is applied, one layer of metal ions slides over the other through the “sea of mobile electrons”