Covalent & Metallic Bonding

Question 1

Define covalent bond

3 pts

Answer 1

• a bond formed by the sharing of electrons between 2 atoms
• when atoms combine by sharing atoms, molecules are formed
• covalent bonds can be formed between atoms of same elements and different elements

Question 2

How are elements arranged in molecules of elements?

Answer 2

• some elements exist as molecules
• e.g. hydrogen, chlorine&oxygen exist as diatomic molecules
• each made up of 2 atoms joined tgt by sharing electrons and by a covalent bond

Question 3

Molecule of elements example: Hydrogen

4 pts

Answer 3

• a H atom has 1 outer electron
• needs 1 more electron to attain stable duplet configuration
• a H atom shares its outer electron with another H atom
• a pair of electrons is shared between both H atoms so a single covalent bond is formed

Question 4

Molecule of elements example: Chlorine

Answer 4

• a Cl atom has 7 outer electrons
• needs 1 more electron to attain stable octet configuration
• a Cl atom shares 1 of its outer electrons with another Cl atom
• a single covalent bond is formed

Question 5

Simple molecular structures

Answer 5

• e.g. bromine

- exist as simple molecules

Question 6

Physical properties of simple molecular structures

Answer 6

• low bp and mp
• generally insoluble in water, soluble in organic solvents
• most do not conduct electricity in any state

Question 7

Simple molecular structures (low mp and bp)

Answer 7

• e.g. bromine mp of 7, bp 59
• within the bromine molecules, bromine atoms held tgt by strong covalent bonds
• between bromine molecules held by weak intermolecular forces
• weak intermolecular forces can be easily overcome
• volatile (evaporate easily)

Question 8

Simple molecular structures (insoluble in water, soluble in organic solvents)

Answer 8

e.g. alcohol, methylated spirits, petrol

Question 9

Simple molecular structures (do not conduct electricity in any state)

Answer 9

-do not have any free-moving ions or electrons to conduct electricity

Question 10

Giant molecular structures

Answer 10

• exist as a giant network of atoms that are covalently bonded
• e.g. diamond, graphite, silicon dioxide
• diamond and graphite are allotropes of carbon (diff forms)

Question 11

Giant molecular structures physical properties

Answer 11

• high mp and bp
• do not conduct electricity (except graphite)
• insoluble in both water and organic solvents

Question 12

Giant molecular structures (high mp, bp)

Answer 12

• consists of a large number of atoms held tgt by strong covalent bonds
• to melt or boil substance, these bonds need to be broken
• requires large amt of energy

Question 13

Giant molecular structures (do not conduct electricity except graphite)

Answer 13

• all outer electrons of atoms used to form covalent bonds

- no free electrons that move thru structure to conduct electricity

Question 14

Giant molecular structures (insoluble in both water and organic solvents)

Answer 14

• atoms held tgt by strong covalent bonds
• any forces of attraction between giant molecular structure and solvent molecules are not strong enough to break strong covalent bonds

Question 15

Diamond

Answer 15

• one of allotropes of carbon
• is hard and has a high mp
• does not conduct electricity

Question 16

Diamond (hard and high mp)

Answer 16

• each carbon atom is covalently bonded to 4 other carbon atoms, which are also bonded to 4 other carbon atoms, forming a 3D structure
• difficult to bring these strong covalent bonds

Question 17

Diamond (does not conduct electricity)

Answer 17

• all outer electrons of carbon atoms used for bonding

- no free electrons to move thru structure to conduct electricity

Question 18

Graphite

Answer 18

• an allotrope of carbon
• soft, slippery, fairly unreactive, good conductor of electricity
• high mp and bp
• soft and slippery
• conducts electricity

Question 19

Graphite (high mp and bp)

Answer 19

• each carbon atom is covalently bonded to 3 other carbon, which are in turn bonded to 3 other carbon atoms
• forms a continuous layer of hexagons
• difficult to break these bonds

Question 20

Graphite (soft and slippery)

Answer 20

• layers of carbon held loosely by weak intermolecular forces of attraction
• layers of carbon atoms can slide over each other when force is applied

Question 21

Graphite (conducts electricity)

Answer 21

• each carbon atom has one outer electron that is not used to form covalent bonds
• these electrons can move freely along layers of one carbon atom to the next
• said to be delocalised
• free-moving electrons allow graphite to conduct electricity

Question 22

Silicon dioxide

Answer 22

• found in sand
• used to make glass due to it hardness and high mp
• has high mp and bp
• does not conduct electricity

Question 23

Silicon dioxide (high mp,bp)

Answer 23

• each silicon atom is bonded to 4 oxygen atoms, each oxygen atom bonded to 2 silicon atoms, forming a 3D structure
• strong covalent bonds are difficult to break

Question 24

Metallic bonds

Answer 24

• in a metal lattice, metal atoms lose outer electrons, become positively-charged ions
• outer electrons no longer belong to any metal atom, said to be delocalised
• outer electrons move freely between metal ions like a cloud of negative charge
• metal lattice structure described as a lattice of positive ions surrounded by a ‘sea of mobile electrons’
• a metallic bond is the force of attraction between positive metal ions and the ‘sea of mobile electrons’

Question 25

Physical properties of metals

Answer 25

• good conductors of electricity
• good conductors of heat
• metals usually have high densities, mp and bp
• malleable and ductile

Question 26

Physical properties of metals (good conductors of electricity)

Answer 26

• atoms of metal are tightly packed
• outer electrons of atoms can break away easily from atoms, able to move freely within the metal lattice
• mobile electrons allow metal to conduct electricity

Question 27

Physical properties of metals (good conductors of heat)

Answer 27

• due to movement of mobile electrons within metal lattice

- heat energy transferred easily by mobile electrons in the structure

Question 28

Physical properties of metals (high densities, mp, bp)

Answer 28

• atoms in metal packed tightly in layers, held tgt by strong metallic bonds
• large amt of energy required to overcome these metallic bonds
• result in high densities, bp, mp

Question 29

Physical properties of metals (malleable and ductile)

Answer 29

• can be hammered into diff shapes (malleable),
• drawn into wires (ductile) without breaking
• when force applied to metal, layers of metal atoms can slide over each other thru the ‘sea of electrons’
• metallic bonding not disrupted