Bonding and Periodic Table: Quick Notes

Atom stability and valence electrons

  • Atoms are most stable when their outer electron shell is full (octet rule for most elements; Hydrogen needs 2 in its first shell).
  • Noble gases have filled shells; this stability guides bonding.
  • For main-group elements, valence electrons roughly equal the group number: valence electrons=group number.\text{valence electrons} = \text{group number}. Example: Na (group 1) → 11 valence electron; Cl (group 17) → 77 valence electrons; O (group 16) → 66 valence electrons.
  • Full outer shell leads to low reactivity; atoms will react to achieve a full shell.

Predicting bonding from the periodic table

  • Metals on the left tend to lose electrons; nonmetals on the right tend to gain electrons.
  • Large differences in electronegativity favor ionic bonding (transfer of electrons).
  • When a metal and a nonmetal bond, electrons are transferred, forming charged ions that attract.

Ionic bonds

  • Electron transfer creates ions: Na+, Cl−\mathrm{Na^+},\ \mathrm{Cl^-}.
  • The electrostatic attraction between oppositely charged ions forms an ionic bond.
  • Example: NaCl\mathrm{NaCl} (sodium chloride).

Covalent bonds

  • Nonmetals share electrons to fill outer shells.
  • Hydrogen and oxygen example: water, H2O\mathrm{H_2O}.
    • Oxygen has valence 66 and needs 22 more; each hydrogen has 11 and needs 11, forming two single covalent bonds (H–O–H).
  • Carbon dioxide: CO2\mathrm{CO_2} with two double bonds (O=C=O).
    • A single covalent bond = 2 shared electrons (one bond pair).
    • A double covalent bond = 4 shared electrons (two bond pairs).
  • Carbon can form up to four covalent bonds because its valence is 44: it can form single, double, or triple bonds.

Metallic bonds

  • In metals, valence electrons are delocalized as a "sea" of electrons around positively charged metal ions.
  • These metallic bonds give properties like malleability and electrical conductivity (e.g., iron, Fe).

Carbon and organic molecules

  • Carbon (atomic number 6) has 66 electrons; outer shell can hold up to 88; valence 44.
  • Carbon forms up to four covalent bonds, enabling diverse structures: chains, branches, rings.
  • Methane: CH4\mathrm{CH_4} (C bonded to 4 H).
  • Carbon dioxide: CO2\mathrm{CO_2} (C double-bonded to two oxygens).
  • Carbon backbones create organic molecules; more than 10710^7 known organic compounds.