Post on 03-Jan-2016
Valence Electrons
Electrons in the outermost energy shell Na has 1 valence electron Mg has 2 valence electrons
Electrons involved in chemical reactions and form chemical bonds with other atoms. Gained or lost by atoms in a reactions
***Except for transition elements, the number of valence electrons for an atom = group number in the periodic table !!!!
Octet Rule
Main group atoms gain/lose electrons in order to achieve a
total of 8 electrons in their outermost electron shell.
Therefore, 8 valence electrons = satisfied atom.
Noble Gases = full octet, not reactive since they don’t need to gain/lose electrons.
Lewis Dot Structures
Named for G.N. Lewis, who developed the octet rule.
Method of representing valence electrons for an atom.
Valence electrons are represented by dots around an element symbol
Electrons shown in pairs, any unpaired electrons are available to be gained/lost in a chemical reaction
Element symbol – nucleus and inner electrons around the atom
Used to describe chemical bonding.
Cations/Anions
What kind of atoms LOSE electrons and become positive?
What kind of atoms GAIN electrons and become negative?
Diatomic Molecules
Always exist in a chemical bond with another atom, even if the atom is of the same element
H2 , N2 , O2 , F2 , Cl2 , Br2 , I2
Lewis Theory of Chemical Bonding
1) Valence electrons participate in chemical bonding.
2) Ionic Bonds form between metals and nonmetals. Valence electrons are transferred to nonmetals and ions are formed.
3) Covalent Bonds form between nonmetals. Bond involves the sharing of valence electrons
4) Most atoms aspire to noble gas configurations Octet rule– 8 valence electrons Exceptions: transition elements, H/Li/Be satisfied with 2
Electronegativity
Ability of an atom to draw electrons to it from another atom
Increase electronegativity, increase electron attraction for that atom
How does this characteristic relate to atomic radii?
Basic Trend: (why? )
What does this atomic characteristic have to do with
chemical bonding? Difference in electronegativity between 2 atoms determines
type of covalent bond. Small/no difference—nonpolar covalent Slight difference—polar covalent Huge difference—ionic bond