T1W6L2

next assessment is first week back term 2

patterns in the periodic table §

• looked at subshells, orbitals.
• apply fundamental knowledge/situations to reactivity of elements and their physical properties.
• valence electrons: outermost electrons of the outermost shell. the electrons engaged in bonding.
• 2 properties of elements:
  • chemical properties.
    • element completely changing it’s appearance when bonding with another element.
  • physical properties.
    • element doesn’t change, it’s physical appearance does.
    • $H2O(l)\rightleftharpoons H2O(s)$
• reactivity of group 1 metals increases as there are more valence electron shells.
• ionisation energy is the name of energy which changes the energy level of electrons.

• trends down the group: §

  • the number of outer shell electrons is the same;
  • the number of complete electron shells increases by one.
  • the atomic radius of the element increases down the group.
  • number of protons increases, and shielding increases down the period (+9, +11, +19)
  • effective nuclear charge therefore remains approximately constant.

The number of a group is the same as the number of eletrons in the outer shell of elements in that group, except for group 0.

• trends across the period §

  - the number of outer shell electrons increases by one;
  - the number of complete electron shells stay the same.
  - the point at which a new period starts is the point at which electrons begin to fill a new shell.
  - atomic radius decreases across the period. the outer electrons are in the same shell but the increasing net nuclear attraction pulls the other electrons closer to the nucleus. this is due to shielding of inner electrons.
  - the increase in radius is due to higher principle energy levels being filled, and valency energy level is located further from the nucleus.
  

  element	Na	Mg	Al	Si	P	S	Cl	Ar
  number of (protons) nuclear charge	+11	+12	+13	+14	+15	+16	+17	+18
  electron configuration	2,8,1	2,8,2	2,8,3	2,8,4	2,8,5	2,8,6	2,8,7	2,8,8
  shielding	10e	10e	10e	10e	10e	10e	10e	10e
  nuclear attraction	+1	+2	+3	+4	+5	+6	+7	+8

• valency §

  • valency is the combining power of an atom and is equal to the number of hydrogen atoms it could combine with or displace from a compound. (hydrogen has a valency of 1)
  • valency is NOT the same as the number of valence electrons. E.g. Nitrogen has 5 valence electrons but it’s valency is 3.

• electronegativity §

  • “ability of an atom to attract bonding pair of electrons in covalent bonds” - miss pilling
    • this definition will serve you well.
  • in a covalent bond between two different elements, the electron density is not shared equally.
  • $C{l}_2$ has bonding pair of electrons, shared equally.
  • HCl has 10 electron shielding, and has effective nuclear charge of 7+. 7+ is more than +, so Hydrogen electrons and HCl electrons are not shared equally.
    • Chlorine is more electronegative.
    • Chlorine has a greater ability to attract a bondy pair of electrons not shared equally than carbon.
    • ${}^{\delta +}H:C{l}^{\delta -}$