A201 L01 Atoms

ATOMIC RADIUS

  • Increases as group descend

ATOMIC STRUCTURE

  • Neutron
  • Proton (+)
  • Electron (-)
  • Arrangement of electron: Electron configuration
  • inner shell (2) valence shell (8)
  • Electrons in inner shells have stronger attraction

Octet rule:

  • Atoms have tendency to have 8 outer electrons,
  • Atoms will lose, share, gain electrons just to fulfill this rule
  • Duplet rule (2 valence electrons, similar)

Isotopes

  • Isotope: different neutron no. , same proton & electron no.
  • Most elements have 2/more isotopes

Relative atomic mass: (isotope mass X %) + (other isotope mass X %) + ,,,,,

  • Moving down the group, increase in valence shells
  • Electrons are further and shielded by electron shells
  • Outermost shell weaker attraction to nucleus
  • Valence electrons not held tightly, increase atomic radius
  • Decreases across period
  • Across period, proton no. increase
  • Nuclear charge increase
  • However, valence shell no. remain constant
  • Experience relative similar shielding effect
  • Valence electron stronger attraction to nucleus
  • Reduce atomic radius

IONIZATION ENERGY

Refers to the removal of 1 mole of valence electron from 1 mole of gaseous atom to produce 1 mole of cation (1+)

Process can repeated,

  • however, more energy is needed as atomic radius decrease,
  • increasing attraction between electron and nucleus

I.E. increases across the grp

  • Across period, proton no. increase, while valence shell no. remain
  • Increase positive charge , and valence electrons have stronger attraction
  • More energy needed to overcome the attraction to remove 1 mole of valence electron

I.E. decreases down the grp

  • Down the group, increase in valence shells
  • Increase shielding effect due to increase inner electrons
  • Valence electrons have weaker attraction to nucleus
  • Less energy needed to overcome the attraction to remove 1 mole of electron

ELECTRON AFFINITY

GROUP 2 METALS

GROUP 1 METALS

GROUP 17 HALOGENS

GROUP 18 NOBLE GAS

Energy released when 1 mole of electron added to 1 mole of gaseous atom to form 1 mole of anion (1-)

The higher the energy release, the more the affinity (love) for electron

Metal and non-metal:
Metals: lower E.A., easier to lose electron due to low valence electron no.
Non-metals: higher E.A. easier to gain electron, valence electron shell closer to nucleus, easier to attract electron

Across the period, electron affinity increase

Down the group, electron affinity decrease

  • Down the group, increase in valence shells
  • Increasing shielding effect due to increase in no.of inner electrons
  • Valence electrons have a weaker attraction to nucleus
  • Lesser attraction to electrons
  • Across period, proton no. increase, while valence shell no. remain
  • Increase positive charge and valence electrons have stronger attraction
  • Electrons are more attracted to the atom, increase electron affinity

Alkali metals.

  • Soft metals
  • Low density
  • Low BP, MP
  • Lowest I.E.
  • Higher reactivity
  • Reactivity increases down the grp

React vigorously with oxygen to form metal oxides
4Na + O2 --> Na2O

React vigorously with water to form metal hydroxides and Hydrogen gas
2Na + H2O --> 2NaOH + H2

All alkali metals react with non-metal to form ionic compound, losing 1 electron (cation 1+)
2Na + Cl2 --> 2NaCl

All reactions are exothermic

Alkaline earth metals

  • Harder, more dense than grp 1
  • Higher BP, MP than grp 1
  • Higher I,E,
  • Less reactive
  • Reactivity increases down the grp

React with non-metals to form ionic compounds, losing 2 electrons (2+)
Ca + Cl --> CaCl

React with water to from metal hydroxides and hydrogen gas
Mg + 2H2O --> Mg(OH)2 + H2

React with with oxygen to form metal oxides
2Ca + O2 --> 2CaO

  • Diatomic molecules
  • High E.A.
  • Forms anions (1-)
  • Reactivity decreases down the group
  • Increase BP, MP down the group
  • Increase in colour down the group

React with metals to from ionic compounds
2Na + Cl2 --> 2NaCl

React with hydrogen gas to from hydrogen halides
Dissociates in water to form acids
H2 + Cl2 --> 2HCL

Reacts slowly with water to oxidize water (fluorine & chlorine)
3F2 + 2H2O --> 6HF + O3 (ozone)
Cl2 + H2O --> HCl + HOCl (hypochlorous acid)

  • Completely filled valence electron shell
  • High I.E.
  • Highly UNREACTIVE
  • Inert gas