Valence electrons are important because…  They are the electrons in the outermost shell  They are the same for each element in a group (column).  Want to follow the octet rule of having 8 electrons in the outer shell.  They are the electrons that are involved in bonding.

 How many electrons would carbon want? gain 4  How many electrons would nitrogen want? gain 3  How many electrons would oxygen want? gain 2

Lewis Structures show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule How do we write them? 1. Write the symbol of the element. 2. Find its number of valence electrons 3. Starting at the right, draw a dot to represent each of the valence electrons and continue counter clockwise until you have used them all up. 4. Each side of the element can only have two dots, because each orbital can only hold 2 electrons 5. Lone electrons tell you how many bonds will form

 Write the symbol for the element, carbon  It is in group 4 so it has how many valence electrons?  Starting at the right, put one dot on each side until you run out of electrons  Count the number of lone electrons to know how many bonds will form C

 Mg  B  O  Ar How many bonds will each element form?

An attractive force between atoms or ions that binds them together Two types of bonds: Ionic bond: bond formed between two ions by the transfer of electrons Covalent bond: bond formed by sharing electrons

 When a metal (+) and a non-metal (-) combine  Oppositely charged ions attract  Soluble in water  Conducts electricity when dissolved

 Found to the right of the staircase  Between two non-metals of similar electronegativity Electronegativity – the ability of an atom of an element to attract electrons when the atom is in a compound

The sharing of electrons can be looked at as a sort of tug- of-war between the nucleus’ of the two atoms involved If that’s the case then who wins? -nonpolar covalent bond – when the atoms in the bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally -polar covalent bond (polar bond) - a covalent bond between atoms in which the electrons are shared unequally. The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.

Difference in electronegativity determines bond type  Above 1.7 = ionic  0.3 – 1.7 = polar covalent  = non-polar covalent Look at periodic table in CRM p.13 Find the difference between the two numbers Which is the more polar covalent? (larger # = more polar) O-O or O-H

Review Ionic- Metal with nonmetal Covalent – Nonmetal with nonmetal What about two metals? Metals do not combine with metals. They form alloys, which is a solution of a metal in a metal Examples: steel, brass, and bronze However Atoms of metal are still held together with…

Metallic bond – bond found in metal; holds metal atoms together very strongly Formed between atoms of metallic elements Good conductors at all states, lustrous, very high melting points