Chapter 5 electrons

Chapter 5 electrons

1. Electron structure

   • Shells are regarded as energy levels
     • Energy increases as shell number increases
       • This is called the principal quantum number
   • Atomic orbitals
     • An atomic orbital is a region around the nucleus that can hold up to two electrons with opposite spins
     • s-orbitals
       • Each shell from n = 1 contains one s-orbital
         • One s-orbital = 2 electrons
     • p-orbitals
       • In the shape of dumb-bells
       • Each shell from n = 2 contains three p-orbitals
         • Three p-orbitals = 6 electrons
     • d-orbitals
       • Each shell from n=3 has 5 d-orbitals
         • So 10 electrons
     • Each shell from n=4 contains 7 f-orbitals
       • So 14 electrons
   • REMEMBER 4S FILLS BEFORE 3D

2. Ionic bonding

   • This is the electrostatic attraction between positive and negative ions. It holds together cations and anions in ionic compounds
   • Metal to non-metal
   • Electrons move
   • Structure of ionic compounds
     • Because ions attracted oppositely charged ions in all directions, they form giant ionic lattice structures
     • Properties of ionic compounds
       • Melting and boiling points
         • High temperature is needed to provide lots of energy that is needed to overcome the strong electrostatic attraction between the ions
         • High
       • Solubility
         • Many ionic compounds dissolve in polar solvents
         • Polar water molecules break down the lattice and surround each ion in solution
         • The ionic lattice must be broken down
           • Water molecules must attract and surround the ions
       • Electrical conductivity
         • In a solid state an ionic compound does not conduct electricity due to fixed position of ions in giant ionic lattice
           • There are no mobile charge carriers

3. Covalent bonding

   • The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
   • This is localised
     • ie no giant ionic lattice formed
   • Electrons are shared
   • Paired electrons that are not shared are called lone pairs
   • Dative covalent bonds
     • This is a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only
   • Bond enthalpy
     • This serves as a measurement of covalent bond strength, the larger the value the stronger the covalent bond