Intro to Agriculture AAEC – Paradise Valley Fall 2014 Chemical Bonds Intro to Agriculture AAEC – Paradise Valley Fall 2014

CHEMICAL BONDING Occurs when 2 or more atoms combine by sharing or transferring electrons. Can be from the same element (O2) or different elements (NaCl) Atoms combine so that they each have a total of 8 valence electrons (full octet)

Valence electrons Chemical bonds are formed only between the electrons in the highest unfilled energy level. These electrons are called valence electrons.

Lewis Dot Diagrams A picture that represents an atom’s valence electrons. Helpful for determining what atoms will bond to form compounds. Element symbol with dots around it for each valence electron (go around once before you pair up dots)

Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 18 H He:            Li Be  B   C   N   O  : F  :Ne :                    Na Mg  Al  Si  P S :Cl  :Ar :        

Practice Problems A. X would be the electron dot formula for  A. X would be the electron dot formula for 1) Na 2) K 3) Al   B.  X  would be the electron dot formula 1) B 2) N 3) P

Chemical Bonding (cont.) 2 types of Chemical Bonds: Ionic Bonds Covalent Bonds

Ionic Bonds Occur when atoms gain or lose electrons to form ions Oppositely charged ions are attracted to each other and form a bond Occur only between metals and nonmetals

Ionic Bonds (cont.) Na+  Cl- forms NaCl Metals form Positive (+) ions because they give away electrons Nonmetals form Negative (-) ions because they gain electrons Opposites Attract: Na+  Cl- forms NaCl

CO2, H2O, NO2 Covalent Bonds Occur when atoms share electrons Rather than lose or gain electrons atoms share their electrons to make a full octet. Only occur between nonmetals. CO2, H2O, NO2

Chemical formulas A molecule’s chemical formula tells you the ratio of atoms of each element in the compound.