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

2. 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)

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

5. 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)

8. Electron Dot Structures
Symbols of atoms with dots to represent the valence-shell electrons
H He:
          
Li Be  B   C   N   O  : F  :Ne :
       
          
Na Mg  Al  Si  P S :Cl  :Ar :
       

9. 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

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

11. 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

12. 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

14. 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

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