The Periodic Table
Patterns in groups
- Ionization energy: Passing down a group, nuclear charge increases, the outer electrons are further
away from the nucleus and are better screened from its attraction by the increased number of
electrons. Hence ionization energy fall.
- increase in metallic character
- similar maximum oxidation state
Group I elements and their compounds
- alkali metal
- s-block elements because have 1 outermost s-electron
- colour: Li (crimson), Na (golden yellow), K (lilac), Rb and Cs (violet-blue)
- electronegativity are very small; large electronegativity between 2 atoms; ionic bond
- reactivity increase down the group because the ease of electron loss increase
- high electrode potential
- strong reducing agent
- store the first 3 elements under paraffin
- compound of alkali metals: crystalline white solid of high melting point that dissolve in water
(a) Oxides: extremely basic, dissolve in water
(b) hydroxide: deliquescent in air, very soluble in water
(c) carbonate: soluble in water and stable to heat (except Li2CO3)
(d) chloride: highly ionic transparent cubic crystals dissolve in water easily
(e) nitrate: evolve oxygen on further heating
- uses:
(a) NaOH: manufacture of soap, detergent etc. and make organic compound e.g. phenol
(b) Na2CO3: sewage treatment, metal refining, textile dying, production of sodium silicate
(c) Potassium compound:
KNO3 - fertilizers, explosive, glass
K2CO3 - glass, soft soap
potassium phosphate - 'builder' to enhance the surfactant performance of detergents
(d) Lithium compound:
Lithium carbonate - antidepressant drug
Lithium hydroxide - ventilation systems of submarines
Group IV elements and their compounds
- electrical conductivity:
diamond (non-conductor), graphite / tin / lead (conductor), silicon / germanium (semiconductor)
- structural changes: from giant molecules lattices to metallic lattices
- first ionization energy: from C to Si, decrease considerably; then fall relatively little afterwards
- oxidation state: +2, +4
- simplified table 1:
| ¡@ | CO2 | SiO2 | GeO2 | SnO2 | PbO2 |
| Preparation |
Direct combination of element and oxygen |
electrolytic oxidation of lead ions (aq) |
|||
| Structure | Simple molecular | Giant molecular | Intermediate between giant molecular and ionic | ||
| Nature | acidic | amphoteric | |||
| Thermal Stability | stable even at high temperature | decomposes on warming | |||
- simplified table 2:
| ¡@ | CO | SiO | GeO | SnO | PbO |
| Preparation | CO2 + C --> 2CO | exist at high temperature | reduction of GeO2 with Ge | heat hydroxide or nitrate | |
| Structure | simple molecular | perdominantly ionic | |||
| Nature | neutral oxide | amphoteric oxide | |||
| Thermal stablity | readily oxidized to dioxide | stable | |||
Group VII elements and their compounds
- electron configuration: ns2np5
- inability to conduct electricity
- oxidizing agent: (strong) F >> Cl > Br > I (weak)
- reaction of halogens with water and base:
(1) fluorine with water: 2 F2 + 2 H2O ---> 4 HF + O2
(2) Disproportionation of Cl, Br and I: a chemical change in which one molecule is simultaneously
oxidized and reduced. e.g. Cl2 (0) + H2O (0) ---> HCl (-1) + HOCl (+1)
(94/4(b)(i)) (97/(13(a)(iv)(1))
(3) Cl and Br have to be stored in brown bottle because the decomposition of halic (I) acid is
accelerated by light. (95/1(a)
- Some uses of halogen- containing compounds in everyday life in everyday life include photographic
film, bleaching agents and tooth pastes.
Patterns in Period
- across the period, melting point of compounds and their electrical conductivity in the liquid state
generally fall.
Transition metal
- general properties:
(1) little change in atomic radii because slightly increase in effective nuclear change
(2) decrease in ionic radii
(3) increase in electronegative
(4) ionization energy increase from Scandium to zinc
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