Periodicity

• Metalloids

  The elements found along the stepped line are known as metalloids or semi-metals. They have a combination of metallic and non-metallic properties.
• Metallic bonding

  • Metals are bonded in giant lattice structure held together strong electrostatic force of attraction between positive ions and free electrons.
  • The strength of metallic bonding depends on: Number of protons, Number of free electrons, Size of ion.
  • Electrical conductivity increases with number of free electrons.
• Covalent bonding

  • Silicon has four valence electrons and due to its giant covalent structure, there are no free electrons. Hence, the electrical conductivity of silicon is less than that of metals.
  • Carbon also has four valence electrons and is available in the form of diamond and graphite.
• The periodic table is arranged in order of increasing atomic number.
• Periodic table blocks

  • s-block, p-block, d-block and f-block
• Helium

  Helium is placed above the Nobel gases. It fits the pattern of chemical reactivity however it is not a p-block element. Its electronic structure is 1s2.
• Reactivity of p-block elements

  Non-metal (p-block) elements get less reactive going down the group.
• Lanthanides

  Metals that are rarely encountered. They form 3+ ions and have similar reactivity.
• Actinides

  Radioactive metals. Most occur in only trace amounts on Earth, apart from Thorium and Uranium.
• First ionisation energy

  The energy required to remove one electron from each atom in one mole of atoms of the element in its gaseous state to form gaseous 1+ ions.
• Factors affecting ionisation energy

  • Size of nuclear charge, Distance of valence electrons from the nucleus (atomic radius), Shielding of inner electrons
• Periodic trend in ionisation energy down a group

  The ionisation energies decrease down the group, despite the increase in nuclear charge. The valence (outer) electrons are shielded by the filled orbitals. The distance between the valence electrons and nucleus also increases down the group, making it easy to remove valence electron.
• Successive ionisation energies

  Removing more than one electron from an atom requires more energy each time. As you move down a main energy level (shell) of electrons, there is a jump in the ionisation energy as the electron is closer to the nucleus and so it is more strongly attracted.
• Trend in melting point and boiling point across period 3

  1. Increases from Na to Si due to increase in strength of metallic bonding.
  2. MP decreases from Si to Ar. Si has highest melting point because of the giant molecular structure.
  3. The covalent bonds of non-metals are strong, the molecules (P4, S8, Cl2) held together by weak van der waals forces. These forces require less energy to break. Thus, gives a relatively much lower melting point than metals.
  4. Argon exists as single atoms held together by weak van der waals forces. This is the reason why argon has the lowest melting point.
• Periodicity is repeating patterns on the periodic table.
• Groups

  • Vertical column of elements.
  • Similar properties
  • Same number of electrons in their highest energy level.
• Reactivity of s-block elements

  • S-block elements get more reactive going down the group.
• Identify the element in Period 4 with the largest atomic radius. Explain your answer. (3)

  Potassium

  • smallest number of protons/smallest nuclear charge
  • similar shielding/same number of shells
• Explain why the atomic radii of elements decrease across period 3 from sodium to chlorine (2)

  • number of protons increases/nuclear charge increases
  • attraction between nucleus and electrons increases
• Periodic trends in ionisation energy

  • The first ionisation energy increases across the period.
  • The nuclear charge increases with the addition of another proton.
  • Each new electron is added to the same electron shell as for the previous element.
  • The atomic radius decreases across the Period.
  • So overall ionisation energy increases as there is a stronger attraction between the valence electron and the nucleus, with no increase in shielding effect.