When two or more atoms really
love each other… they bond 
Chemical Bonds
 Attractions arising from the sharing or transfer of
valence electrons.
 Bonds can be INTER-molecular or INTRA-molecular
 Intramolecular: within a molecule
 Covalent – sharing
 Ionic – transferring
Covalent Bonds
 Sharing of a pair of valence electrons.
 2+ atoms covalently bonded = MOLECULE
 Pure substances vs. Compounds
 H2

H2O
More on covalence…
 Electronegativity: attraction of a particular atom for
the electrons of a covalent bond.


Nonpolar covalent bonds: when electrons share equally
Polar covalent bonds: when electrons are not shared equally
Ionic Bonds
 Occurs when there’s an imbalance in electrons
 When electrons are transferred, ions are formed
Types of ions
 Ions = charged particles

Cation = positive ion


 Break down these ions:
Na+
Anion = negative ion

Cl-

MgO

K2O

CaCl2
Ionic Compounds = Salts
 Environmental conditions impact strength of ionic
bonds.

Dry conditions: Ionic bonds are stronger

In water: ions dissociate (water = universal solvent)
Weaker Chemical Bonds
 Hydrogen bonds: Attraction of “charged” hydrogen
bonded with another atom to another different atom
nearby.
Weaker Chemical Bonds
 Van der Waals Interactions: Electrons distribute
unevenly creating slightly positive and negative
regions.
Molecular Shape and Function
 Molecular shape dictates their function in ALL of
biology!
 Ex: Proteins, hormone receptors, blockers
Chemical Reactions
 Formation and destruction of
chemical bonds are called
chemical reactions.
 Reactants: starting materials
 Products: materials after
chemical conversion
Photosynthesis & Cellular Respiration
 Photosynthesis:
 6CO2 + 6H2O  C6H12O6 + 6O2
Photosynthesis & Cellular Respiration
 Photosynthesis:
 6CO2 + 6H2O  C6H12O6 + 6O2
 Cellular Respiration:
 C6H12O6 + 6O2  6CO2 + 6H2O + ENERGY!!!!!
Chemical reactions are reversible! These are examples!