Metallic + Ionic Bonding

Question 1

Bonding v Structure

Answer 1

B: forces between species - specifically electrostatic attraction between a + & -

S: arrangement of atoms into molecules or giant lattices
*molecules - simple covalent structures

Question 2

Metallic bond definition?

Answer 2

the electrostatic force of attraction between + metal ions (cations) and sea of delocalised electrons

Question 3

Melting temperatures of metals?

Answer 3

to melt metal, necessary to overcome electrostatic forces of attraction between nuclei of cations & delocalised sea of electrons so - cations free to move around structure
- giant lattice structure so where many of forces must be overcome - large energy

Question 4

Factors affecting melting temps of metals?

Answer 4

• the more electrons atom can donate to delocalised system, the higher mp/no. delocalised electrons per cation (G1<G2<d-block)
• the size of the cation/ionic radius (so-greater density): the smaller, the closer delocalised electrons to nucleus of cation - increase in forces of attraction…

Question 5

High electrical conductivity of metals?

Answer 5

• electrons in the delocalised sea of electrons r free to move/mobile & so carry electrical charge so - current

Question 6

Thermal conductivity of metals?

Answer 6

• free-moving delocalised electrons pass K.E. along metal
• cations r closely packed & pass K.E. from one cation to another

Question 7

Malleability (hammered/pressed) & ductility (drawn into wire) of metals?

Answer 7

• cation layers can slide when stress & still retain attraction between ions & delocalised electrons
• since delocalised electrons free moving - move w cations & prevent strong forces of repulsion forming between cations in 1 layer and cations in another

Question 8

Metallic structure?

Answer 8

• lattice of cations surrounded by sea of delocalised electrons
  *lattice = repeating arrangement

Question 9

Ionic bonding definition?

Answer 9

the electrostatic force of attraction between 2 oppositely charged ions
- involves electron transfer usually to form an electron configuration like noble gas

Question 10

Molecular ions & their formulae?

Answer 10

• hydroxide OH-
• nitrate NO-
• ammonium NH4+
• sulphate SO4 2-
• CO3 2-

Question 11

Giant ionic structure?

Answer 11

lattice of alternating anions & cations
- ‘rock salt structure’ aka each anion is surrounded by 6 cations & each cation surrounded by 6 anions
- regular structure
- cubic shape
- giant repeating pattern
- electrostatic attractions>electrostatic repulsions (between ions of same charge)
- electrostatic interaction is non-directional - direction of bonding doesn’t affect bond (all that matters is distance between 2 ions)

Question 12

Determining the strength of ionic bonding?

Answer 12

by calculating amount of energy required, in 1 mol of solid, to separate the ions to infinity (i.e. gas phase) (infinity dis from 1 another: ions can no longer interact)

Question 13

Factors affecting the strength of ionic bonding… size of ions

Answer 13

• size determines how closely packed ions are in lattice
• for ions of same charge (e.g. F- & Cl-): smaller the ions, the more energy required to overcome the electrostatic interactions between ions & separate them

Question 14

Factors affecting the strength of ionic bonding… the size of charge

Answer 14

• the larger the charge on ion, the stronger ionic bond aka electrostatic attraction
• when both cation & anion are 2 charged - energy even greater than e.g. Li+ & O2-

Question 15

Charge density?

Answer 15

• the smaller the ion + the higher the charge, the stronger the electrostatic attraction so - the higher the mp
• (big charge + small ion - higher charge density)
• (small charge + big ion - smaller charge density)

Question 16

Trends in ionic radii?

Answer 16

(* vary according to ion environment e.g. how many oppositely charged ions r touching it/nature of ions - should come from same source e.g. website)
- as you go down each group, ions have more electron shells, so - radius increases
- as you go across each period (no. protons increases) ionic radius decreases (electrons r attracted more strongly so - pulled closer to nucleus)

Question 17

Isoelectric ions?

Answer 17

different atoms that have same no. electrons
- ionic radius decreases as atomic no. increases because: attractive form from nucleus increases (more protons) - pulls in outer electron shell more
* outer shell the same for all isoelectric ions

Question 18

Most ionic compounds are soluble in water…

Answer 18

• water molecules r polar so - attract + & - ions & break up structure
• O end of water molecules attracted to + ions
• H end of water molecules attracted to - ions

Question 19

Electrical conductivity of ions…

Answer 19

• solid ionic compounds don’t - no delocalised electrons & ions not free to move
• molten (& aq) will - ions mobile & will migrate to electrodes of opp sign when pd (if dc - electrolysis & ions discharged as electrodes)

Question 20

High melting temperatures of ionic compounds…

Answer 20

• many strong electrostatic forces between oppositely charged ions - lots of energy needed to overcome these forces (for ions to break free from lattice & slide over e/o)

Question 21

Brittleness of ionic compounds?

Answer 21

• if stress applies to crystal of ionic solid - layers of ions may slide over e/o…
• ions of same charge now side by side & repel one another so - crystals break apart

Question 22

Evidence for the existence of ions

Answer 22

• the ability of an ionic compound to conduct electricity & undergo electrolysis when molten/ in aqueous solution
• movement of ions demonstrated by: passing dc thru GREEN copper(II) chromate(VI) solution…
• aq Cu 2+ ions = blue, aq CrO4 2- ions = yellow
• Cu 2+ migrate towards - cathode & solution around electrode turns blue
• CrO4 2- migrate towards + anode - solution around turns yellow
• or CuCrO4 placed on wet filter paper & electricity passed thru - ions start to separate