s2.1 - ionic model

Question 1

define ionic bonding

Answer 1

electrostatic attraction between oppositely charged ions. metals lose electrons and the electrons are transferred to non-metals

Question 2

define covalent bonding

Answer 2

electrostatic attraction between a shared pair of electrons and the positively charged nuclei

Question 3

define metallic bonding

Answer 3

electrostatic attraction between a lattice of positive ions and delocalised electrons

Question 4

what is an ion?

Answer 4

an ion is an electrically charged species that is formed after an atom gains or loses electrons. they obtain the same electron configuration as the stable noble gases

Question 5

define isoelectronic

Answer 5

sharing the same electron configuration

Question 6

what are cations?

Answer 6

cations (positive ions) form when electrons are lost. the energy associated with this is known as ionisation energy

Question 7

what are anions?

Answer 7

anions (negative ions) form when electrons are gained. the energy associated with this is known as electron affinity

Question 8

what are transition metal ions?

Answer 8

transition elements can form more than one positive ion. this is because they lose their electrons from the 4s subshell first

Question 9

how do you name binary ionic compounds?

Answer 9

the cation is listed first (same as the neutral element)
the anion is listed second (suffix changes to -ide)

Question 10

what is a polyatomic ion?

Answer 10

a group of covalently bonded ions

Question 11

list all the polyatomic ions

Answer 11

ammonium - NH₄⁺
hydroxide - OH⁻
nitrate - NO₃⁻
hydrogen carbonate - HCO₃⁻
carbonate - CO₃²⁻
sulphate - SO₄²⁻
phosphate - PO₄³⁻

Question 12

what is electronegativity?

Answer 12

electronegativity is a measure of the ability of an atom to attract a pair of electrons. electronegativity values can also be used to determine whether an ionic compound will result from two specific elements reacting together. it is generally recognised that a difference of 1.8 units or more on the pauling scale will give a compound that is predominantly ionic

Question 13

what is the structure of ionic compounds?

Answer 13

the structure of ionic compounds is a giant ionic lattice. each ion is surrounded by oppositely charged ions. these ions attract each other from all directions (meaning it is non-directional)

Question 14

what is lattice enthalpy?

Answer 14

lattice enthalpy (ΔHθₗₑ) is the enthalpy change when 1 mole of an ionic lattice is broken down into it’s gaseous ions under standard conditions (273.15K and 100kPa)
the enthalpy change is positive, so ionic lattice breakdown is endothermic

Question 15

what do lattice enthalpy values mean?

Answer 15

lattice enthalpy values indicate the relative strength of ionic bonds (more endothermic lattice enthalpy values means stronger ionic bonds)

Question 16

how does ionic size impact lattice enthalpy?

Answer 16

ΔHθₗₑ decreases with increasing ionic radius. as the ionic size increases, there is weaker electrostatic attraction between the ions, so the lattice enthalpy will be less endothermic

Question 17

how does ionic charge impact lattice enthalpy?

Answer 17

ΔHθₗₑ increases with increasing ionic charge. increased ionic charge will result in a stronger electrostatic attraction. this will result in a more endothermic lattice enthalpy and a higher melting point

Question 18

why do ionic compounds have a high melting point?

Answer 18

ionic compounds have high melting and boiling points due to having strong ionic bonding so ionic compounds are solid at room temperature. a larger ionic charge or a smaller ionic radii produces stronger ionic bonds, which results in a higher melting point

Question 19

why are ionic compounds brittle?

Answer 19

ionic compounds are brittle as when a force is applied, the layers of the lattice move and similar charged ions will be next to each other, causing a repulsion split

Question 20

do ionic compounds conduct electricity?

Answer 20

ionic compounds do not conduct electricity when solid as the ions are not mobile. however, ionic compounds do conduct when molten or in aqueous solution as the ions become mobile and conduction takes place

Question 21

why are ionic compounds soluble?

Answer 21

solvents like water are called polar solvents because they have partial charges so ionic compounds can dissolve in them. non polar solvents (e.g. hexane) do not have partial charges and therefore cannot dissolve ionic compounds
when an ionic compound is added to water, the water molecules position themselves so that their partial charges attract the oppositely charged ions in the compound
ionic compounds are insoluble in water when the electrostatic attraction between the cation and the anion is stronger than between the ion and the water