bonding, structure and properties

Question 1

Describe the properties of a covalent molecular substance

Answer 1

Low Mp and Bp
Soluble in a non-aqueous solvents (white spirit)
Never conductive
Made of molecules (neutral)
Liquid or gas at room temp (weak intermolecular forces)

Question 2

what are the 4 shapes of molecules

Answer 2

linear, angular, trigonal pyramidal and tetrahedral

Question 3

what is a molecule

Answer 3

a group of atoms held together by covalent bonds

Question 4

what is a covalent bond

Answer 4

bond between two non metals
strong bond formed between atoms as a result of electrostatic attraction between the positive nuclei and the pairs of negative elections which are shared
only the outer electrons are involved in bonding

Question 5

what and why are noble gases

Answer 5

group 8 of the periotic table

they are unreactive element due to their full outer shell of electrons

Question 6

what are the rules of electron shells/ energy levels

Answer 6

the first level can only have 2 electron, the others can have up to 8 - only draw the outer shell when drawing the bonds between atoms

Question 7

why do atoms form bonds

Answer 7

to gain or loose outer electrons to get a full outer shell - to reach the same stable outer electron arrangement as a noble gas

Question 8

what is a valency

Answer 8

the valency is the number of bonds an atom can make

Question 9

what are the 2 possible structures for a covalent substance

Answer 9

covalent networks or covalent molecular substances

Question 10

explain what a covalent network is

Answer 10

when all atoms in the substance are connected together by covalent bonds e.g. diamond & graphite
due the strong covalent bonds

Question 11

explain what a covalent molecular substance is

Answer 11

covalent molecules are atoms connected by covalent bonds. The molecules are separate to each other and held together by (usually weak) intermolecular bonds/forces
strong bonds within the molecule

Question 12

what do the terms aqueous, solvent and solute mean

Answer 12

aqueous = dissolvible in water
solvent    = dissolver 
solute     = dissolved

Question 13

what is the solubility of covalent compounds like ?

Answer 13

most covalent compounds dissolve in non-aqueous solvents

Question 14

what is electricity

Answer 14

electricity is the flow of charged particles (electrons) around a circuit from negative - to positive =

Question 15

what is the conductivity of covalent substances

Answer 15

most covalent substances don’t conduct (graphite does)

Question 16

what charge will a metal ion have

Answer 16

positive charge (loses electrons)

Question 17

what charge will a non-metal ion have

Answer 17

negative (gains electrons)

Question 18

what is an ionic compound / what is an ionic bond

Answer 18

ionic compounds contain both metal (positively charged) and non-metal (negatively charged ions)
Ionic bonding is the electrostatic attraction between the positive (metal) and negative (non-metal) ions

Question 19

what structure is a ionic compound arranged in?

Answer 19

a lattice (non-metal/negative ions are bigger, metal/positive ions are smaller)

Question 20

what does variable valency mean ? and what group does the term apply to?

Answer 20

the transition metals (group 2) - the amount of outer electrons can vary

Question 21

what state and why are ionic compounds at room temperature

Answer 21

solid because lots of energy is required to break the strong ionic bonds (electrostatic forces/attraction) between the positively and negatively charged ions.

Question 22

describe the solubility of ionic compounds or salts

Answer 22

when ionic compounds or salts dissolve in water the ionic lattice breaks up to give ions that are free to move and are surrounded by water molecule
these compounds dissolve in water to give an aqueous solution

Question 23

describe the conductivity of ionic compounds

Answer 23

ionic compounds conduct electricity when in an aqueous solution, they also conduct when melted (liquid)
They can conduct when molten or as a solution as the ions (charged particles) are free to move

Question 24

What is electrolysis?

Answer 24

the process of passing electricity through an ionic melt/solution to split the elements - used in chemical industry for extracting an purifying metals from their ores
the solution/melt is called the electrolyte

Question 25

how do metals conduct electricity?

Answer 25

by allowing the free electrons to move between the atoms

Question 26

Describe the properties of a covalent network

Answer 26

High MP and BP (strong bonds)
cannot dissolve in water 
Never conductive (expect graphite)
Made of molecules (neutral)
Solid at room temp (carbon, silicon dioxide)

Question 27

Describe the properties of an ionic compound

Answer 27

very High MP and BP
Soluble in water 
Only conducts when melt or solution (charged particles - ions are free to move) 
Solid at room temp 
Made of ions