chemistry

• if outermost shell is full, atom is stable and unreactive
• group 18- noble gases

  group 17- halogens

  group 1- alkali metals
• duplet electronic configuration is ..2, octet electronic configuration is 2,..., 8
• to achieve full valence shells, atoms chemicaly combine to form bonds, through

  • loss of electrons
  • gain of electrons
  • sharing of electrons
• ions are formed when atoms gain/lose electrons. metals usually form cations by losing electrons and non metals usually form anions by gaining electrons.
• ions of opposite chargers can join by ionic bonding.
• ionic bonding is the mutual electrostatic attraction between ions of opposite charges.
• what are ionic compounds held together by?

  ionic bonds
• in most cases, ionic bonds form between metals and nonmetals.
• what is a giant crystal lattice?

  3D structure of alternating anions and cations regularly spaced held together by ionic bonds
• ionic structures-

  • cations and anions exert electrostatic forces all around themselves
  • cations already attached to anions will continue electrostatically attracting anions
• covalent bonding?

  is the sharing of electrons.
• valency refers to number of electrons that must be lost, gained or shared to attain noble gas electronic configuration.
• In covalent bonding, since atoms are shared so closely, covalent bonds hard to break.
• covalent molecules are mostly simple molecules with countable number of atoms in a fixed ratio.
• some covalent substances exist as giant molecules which have practically uncountable no. of atoms in each molecules
• metallic bonding- how metals are held together.
• in solid state, metal atoms form a giant metallic lattice structure.
• • metal atoms lose outermost electrons and become cations
  • these unbonded electrons are delocalised
  • they are mobile, move freely between ions
• the metallic bond is the mutual electrostatic attraction between cations in a metal and the " sea of delocalised electrons"
• draw sodium chloride, chlorine (2), sodium