 Electrostatic attraction between pairs of atoms or ions  Why do chemical compounds form?  A chemical bond will form if a combination of atoms has a lower energy state than the individual atoms.  2 options  Transfer of electrons = ionic bonding (e.g. NaCl, LiF)  Sharing of electrons = covalent bonding (two types)

 Main group metals (I and II)  Lose electrons to have an outer electron configuration like the nearest Noble Gas  Non-metals  Gain electrons to fill their outer shell  Resembles the nearest Noble Gas

 Show only the outer shell (valence) electrons (Roman numerals under Group #)  Also called electron dot diagrams  The element symbol represents (e.g. Na)  The nucleus (protons and neutrons)  The inner electrons

1. Draw the element symbol 2. Electrons are placed on all 4 sides of the symbol It doesn’t matter what side you start on ie. Are all correct!!! 3. Place one electron on each side first and then doubling them until all electrons are placed Remember: Group # = valence electrons, if there are 2 digits, use the 2 nd. Eg. Group 17 = 7 valence electrons

 Draw Lewis diagrams for the following elements: Ca, Mn, Au, Al, P, Ar, O, H

 Walter Kossel  Hypothesized that elements form compounds to reach a more stable electron configuration.  For this to happen we need a donor electron  Who gains and who loses?

 Elements with low ionization energies lose  Where are these located on the periodic table?  Elements with high electron affinities gain electrons  Where are these located on the periodic table?  The resulting ionic compounds are held together by electrostatic attraction  Opposites Attract

Note: Each ion ends up with a valence electron configuration like the nearest Noble Gas.

 Ionic compounds form a 3-dimensional array called a crystal lattice.  Alternating positive and negative ions

 The ionic radius of a cation is less than that of the corresponding atom.  Why?  Remember, cations have lost their outer electrons.  The ionic radius of an anion is greater than that of the corresponding atom.  Why?  Remember, anions have gained electrons in their outer shell

 Compounds that conduct electricity in a molten state (melted) or in solution.  Ionic compounds are electrolytes.  As solids the ions are held together, in liquids they can flow and conduct electricity.