Periodic Table and Periodicity - Summary

History of the Periodic Table

  • Brief history.

Periodic Table

  • Period: Horizontal rows (series).
  • Group: Vertical columns (families).
  • Elements in the same group have similar properties; groups are numbered 1-18.
  • Elements in the same period do not have similar properties, but they have the same number of occupied energy levels; periods are numbered 1-7.
  • Common names for specific groups:
    • Group 1: Alkali metals
    • Group 2: Alkaline earth metals
    • Group 17: Halogens
    • Group 18: Noble gases

Metals vs. Nonmetals

  • Metals (left of staircase):
    • Lustrous (shiny)
    • Malleable (hammer into thin sheets)
    • Ductile (make into thin wire)
    • Good conductors of heat and electricity
  • Nonmetals (right of staircase, including hydrogen!):
    • Non-lustrous (dull)
    • Brittle (breaks easily)
    • Poor conductors (good insulators)

Metalloids (Semi-metals)

  • Touch the staircase and have properties of both metals and nonmetals.
  • Semiconductors: Normally do not conduct electricity but will conduct at high temperatures or when certain substances are added.

Ionization Energy (I.E.)

  • The amount of energy required to remove an electron from a gaseous atom.
  • Depends on:
    • Distance between valence electron and nucleus
    • Effective nuclear charge (# of protons)

Periodic Table Trends

  • Trends include atomic radius, ionization energy, electron affinity, metallic character, and nonmetallic character.

Group 2 | Alkaline Earth Metals

  • Fairly soft metals with fairly high melting and boiling points.
  • Atoms have 2 valence electrons.
  • React by losing electrons to form positively charged cations.
  • Ease of ionisation increases moving down the group.
  • Reactivity with oxygen, water, and dilute hydrochloric acid increases moving down the group.

Reactions

  • Magnesium (Mg): Reacts slowly with air, vigorously with dilute hydrochloric acid, and very slowly with cold water.
  • Calcium (Ca): Reacts readily with air, vigorously with cold water and dilute hydrochloric acid.
  • Barium (Ba): Reacts very readily with air, very vigorously with cold water and violently with dilute hydrochloric acid

Group 7 | Halogens

  • Exist as diatomic molecules and are poisonous.
  • Generally soluble in non-polar solvents and slightly soluble in water.
  • Low melting and boiling points.
  • Atoms have seven valence electrons and readily accept an electron to form negatively charged non-metal anions.

Physical Properties of first four elements in group VII

  • Fluorine: pale yellow gas
  • Chlorine: yellow-green gas
  • Bromine: red-brown liquid
  • Iodine: grey-black solid, sublimes into purple vapor
  • Ease of ionisation and reactivity increases moving up.
  • Oxidizing power increases moving up.

Displacement Reactions

  • A more reactive element will displace a less reactive element.
  • Oxidizing power is determined by how easily one atom takes electrons from another.

Period 3 Trends

  • Metallic nature decreases, and non-metallic nature increases from left to right.
  • Ease of ionisation and reactivity of metals decreases from left to right.
  • Ease of ionisation and reactivity of non-metals increases from left to right.
  • Silicon does not usually ionise (reacts by sharing electrons).
  • Argon does not ionise and is chemically unreactive.
  • Atomic radius decreases moving from left to right due to the increase in the number of positive protons.