ELECTRONS,BONDING AND STRUCTURE

ELECTRONS,BONDING AND STRUCTURE

1. ELECTRONIC STRUCTURE

   • Electrons move around the nucleus in shells (sometimes called energy levels)
     • These shells are all given numbers known as principal quantum number
       • Shells further from the nucleus have a greater energy level than shells closer to the nucleus
       • The shells contain different types of subshells. These subshells have different numbers of orbitals, which can hold up to 2 electrons
         • An orbital is the bit of space that an electron moves in
   • ELECTRON CONFIGURATION
     • Electrons fill up the LOWEST energy sub-shells first
     • The 4s sub-shell has a lower energy level than the 3d sub-shell, even though its principal quantum number is bigger. This means the 4s sub-shell fills up first
     • Electrons fill orbitals singly before they start sharing
     • For the configuration of ions from the s and p blocks of the periodic table, just remove or add the electrons to or from the highest - energy occupied sub-shell E.g. Mg2+ = 1s^2 2s^2 2p^6, Cl- = 1s^2 2s^2 2p^6 3s^2 3p^6
   • The s block element (Group 1 and 2) have 1 or 2 outer electrons. These are easily lost to form positive ions with a inert gas configuration E.g. Na: 1s^2 2s^2 2p^6 3s^1 --> Na+ : 1s^2 2s^2 2p^6
   • The elements in Group 5,6 and 7 (in the p block) can gain 1,2 or 3 electrons to form negative ions with an inert gas configuration E.g. O: 1s^2 2s^2 2p^4 --> O2-: 1s^2 2s^2 2p^6

2. IONISATION ENERGIES

   • Ionisation is the removal of one or more electrons
   • The FIRST IONISATION ENERGY is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atom to form 1 mole of gaseous 1+ ions
     • Equation for the first ionisation of oxygen: O(g) --> O+ (g) + e-
       • You must use the gas state symbol,(g)
     • The second ionisation energy is the energy needed to remove 1 electron from each ion in 1 mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions
       • Equation for the first ionisation of oxygen: O+(g) --> O2+(g) + e-
   • FACTORS AFFECTING IONISATION ENERGY
     • NUCLEAR CHARGE: The more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the elctrons
     • DISTANCE FROM THE NUCLEUS: Attraction falls off very rapidly with distance.An electron close to the nucleus will be much more strongly attracted than one further away
     • SHIELDING: As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feels less attraction towards the nuclear charge. The lessening of the pull of the nucleus by inner shells of electrons is called shielding
   • SUCCESIVE IONISATION ENERGIES SHOW SHELL STRUCTURE
     • The big jumps in ionisation energy happens when a new shell is broken into - an electron is being removed from a shell closer to the nucleus

3. ionic bonding

   • AN IONIC BOND IS AN ELECTROSTATIC ATTRACTION BETWEEN TWO OPPOSITELY CHARGED IONS
   • COMPOUND IONS
     • NITRATE - NO3-
     • CARBONATE - CO3 ^2-
     • SULFATE - SO4 ^2-
     • AMMONIUM - NH4^+

4. COVALENT BONDING

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