Bonding v Structure
B: forces between species - specifically electrostatic attraction between a + & -
S: arrangement of atoms into molecules or giant lattices
*molecules - simple covalent structures
Metallic bond definition?
the electrostatic force of attraction between + metal ions (cations) and sea of delocalised electrons
Melting temperatures of metals?
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
Factors affecting melting temps of metals?
- 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…
High electrical conductivity of metals?
- electrons in the delocalised sea of electrons r free to move/mobile & so carry electrical charge so - current
Thermal conductivity of metals?
- free-moving delocalised electrons pass K.E. along metal
- cations r closely packed & pass K.E. from one cation to another
Malleability (hammered/pressed) & ductility (drawn into wire) of metals?
- 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
Metallic structure?
- lattice of cations surrounded by sea of delocalised electrons
*lattice = repeating arrangement
Ionic bonding definition?
the electrostatic force of attraction between 2 oppositely charged ions
- involves electron transfer usually to form an electron configuration like noble gas
Molecular ions & their formulae?
- hydroxide OH-
- nitrate NO-
- ammonium NH4+
- sulphate SO4 2-
- CO3 2-
Giant ionic structure?
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)
Determining the strength of ionic bonding?
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)
Factors affecting the strength of ionic bonding… size of ions
- 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
Factors affecting the strength of ionic bonding… the size of charge
- 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-
Charge density?
- 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)
Trends in ionic radii?
(* 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)
Isoelectric ions?
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
Most ionic compounds are soluble in water…
- 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
Electrical conductivity of ions…
- 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)
High melting temperatures of ionic compounds…
- 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)
Brittleness of ionic compounds?
- 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
Evidence for the existence of ions
- 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
