S2.1 The Ionic Model

Question 1

what is an ion

Answer 1

a charged particle
- it has a charge as the number of protons do not equal the number of electrons
- forms when an atom gains or loses electrons

Question 2

what is a cation

Answer 2

a positively charged ion
- forms when a metal atom loses electrons

Question 3

what is an anion1

Answer 3

a negatively charged ion
- forms when a non-metal gains electrons

Question 4

what is ionic bonding

Answer 4

the electrostatic attraction between oppositely charged ions in a lattice

Question 5

what is a formula unit

Answer 5

the empirical formula for an ionic compound

Question 6

ammonium + charge

Answer 6

NH4+

charge: +1

Question 7

hydroxide + charge

Answer 7

OH-

charge: -1

Question 8

nitrate + charge

Answer 8

NO3-

charge: -1

Question 9

hydrogencarbonate + charge

Answer 9

HCO3-

charge: -1

Question 10

carbonate + charge

Answer 10

CO3 2-

charge: 2-

Question 11

sulfate + charge

Answer 11

SO4 2-

charge: 2-

Question 12

phosphate + charge

Answer 12

PO4 3-

charge: 3-

Question 13

what is the lattice enthalpy

Answer 13

• strength of the electrostatic attraction between ions in an ionic compound

the enthalpy change when one mole of a solid ionic compound breaks down to form individual gaseous ions

Question 14

the larger the lattice enthalpy…

Answer 14

the stronger the ionic bond

Question 15

the lower the lattice enthalpy…

Answer 15

the weaker the ionic bond

Question 16

physical properties of ionic compounds

Answer 16

• high melting point
• soluble in water
• conducts only when molten or in solution
• low volatility
• brittle

Question 17

explain why ionic compounds have high melting points

Answer 17

• melting an ionic compound involves breaking the electrostatic forces between oppositely charged ions in the lattice
• a lot of energy required to do so due to the strength and the number of electrostatic attractive forces between ions

Question 18

what is volatility

Answer 18

the tendency of a substance to undergo evaporation

Question 19

explain low volatility of ionic compounds

Answer 19

• high melting point
• do not easily evaporate

Question 20

what defines the solubility of an ionic compound

Answer 20

strength of the attraction between the ions and water along with the strength of the ionic bond

Question 21

when is an ionic compound insoluble in water

Answer 21

when it does not form a homogeneous mixture when added to water

Question 22

what is electrical conductivity

Answer 22

the ability of charges species to move through a region of space

Question 23

why are solid ionic compounds not electrically conductive

Answer 23

because the lattice structure in the solid state prevents movement of the charged ions

Question 24

why are molten ionic compounds electrically conductive

Answer 24

• the ionic bonds holding oppositely charged ions begin to break
• cations and anions are allowed to move throughout the liquid

Question 25

why aqueous ionic compounds are electrically conductive

Answer 25

- ions surrounded by water - ions no longer in fixed positions, so they are free to move throughout the solution

Question 26

why are ionic compounds brittle

Answer 26

- when stress is applied, layers within the lattice shift - as layers shift, ions become adjacent to like charges, so they experience an electrostatic repulsion and the layers separate from one another