1. Chemistry Review
Chemical Bonds Elements form bonds in order to gain, lose or share electrons so that they have a full outer energy level.

2. Magnesium: Atomic number 12
1st energy level holds up to 2 electrons 2nd energy level holds up to 8 electrons 3rd energy level is stable with 8 in 1st 2 sublevels (holds 18 total electrons)
Magnesium: Atomic number 12

4. 2 Types of Chemical Bonds
Ionic Bond:
Transfer of electrons
Forms charged ions
Atom that gains an electron becomes a negative ion.
Atom that loses electron becomes a positive ion.
Ions held together by attraction of opposite charges.
Covalent Bond:
Atoms share electrons

5. Nonpolar covalent bond:
Covalent bonds may be either polar or nonpolar.
Nonpolar covalent bond:
Electrons are shared equally between the atoms.
Example: methane (CH4)
Polar covalent bond:
Unequal sharing of electrons because one element has a stronger electronegativity.
The unequal sharing causing the molecule to have charged poles. (Negative on the side with the stronger attraction to the electrons.)
Examples:
Water (H2O)
Ammonia (NH3)

6. Water is a polar molecule.
Oxygen has a greater attraction to the shared electron than the hydrogen does.
Oxygen pole is negatively charged
Hydrogen pole is positively charged

7. Hydrogen bonds: the attraction between opposite poles of two polar molecules.
Example: forms between + hydrogen pole of 1 water molecule and – oxygen pole of another water molecule.
Hydrogen bonds: the attraction between opposite poles of two polar molecules.
Example: hydrogen bonds form between + hydrogen pole of 1 water molecule and – oxygen pole of another water molecule.
Note: hydrogen bonds are attractions between molecules (or distant parts of a large molecule)
They are not the bonds that hold together a molecule.

8. Hydrogen Bond Animation

9. Ionic Covalent Polar Nonpolar Molecular Bonds
Hydrophilic: Hydrophobic: “Water loving” – attracted to charged poles of H2O “Water fearing” Soluble or affinity to water Insoluble
Ionic
Covalent
Polar
Nonpolar

10. Special Properties of H2O
Water is cohesive (attraction between like particles)
Water molecules are held together by hydrogen bonds.
Surface Tension
Water is adhesive (attraction between different particles). Due to its charged poles, water is attracted to other polar molecules.
Capillary Action

11. Water resists temperature change.
Water has a high specific heat which means it takes extra energy to heat compared to other substances, and it also cools down more slowly.
This property is due to the fact that it takes extra energy to break the hydrogen bonds.
Coastal areas often have milder climates due to this property.

12. Water is a good solvent. (A solvent is a substance that is capable of dissolving a solute.
Many ionic (such as salt) and polar (such as
sugar) substances dissolve in water.

14. pH Scale The pH scale ranges from 0 to 14.
A pH of 7 is neutral H+ = OH-
A pH below 7 is acidic greater H + (H+ > OH-)
A pH above 7 is basic greater OH- (H+ < OH- )
Each step in pH scale is a 10 fold change (logarithmic scale)

16. How does a pH of 5 compare to a pH of 7? It is 2 x more acidic
It is 2 x less acidic
It is 20 x less acidic
It is 100 x less acidic
Answer = C 100 x more acidic
10x 10 = 100 x

17. CH4 + 2O2 CO2 + 2 H2O Reactants Products
Chemical Reactions
CH4 + 2O2 CO2 + 2 H2O Reactants Products
Subscript :
The number below the symbol for an element in the formula of a molecule. It represents the number of atoms of that element found in the molecule.
Subscripts
CH4 + 2O CO2 + 2 H2O
Coefficients
Coefficient:
The number in front of a formula for a molecule, in a chemical equation. It indicates the number of molecules that involved in the chemical reaction.

19. Balancing Chemical Equations
Equations must be balanced:
The number/type of atoms on the reactants side must be equal to that on the products side.
Atoms are not created or destroyed in a reaction.
C6H12O6 + __O ___CO2 + __ H2O
(6 carbons, 12 hydrogen, 18 oxygen on each side)

20. Metabolism: All of the chemical reactions that happen in an organism
Metabolism: All of the chemical reactions that happen in an organism. These reactions build up or break down molecules that are important for the functioning of the organism.

21. Special Properties of Water
Water is a polar molecule:
Unequal sharing of electrons. Oxygen pole has partial negative charge and hydrogen pole has partial positive charge.
Water is a good solvent:
Ionic and polar molecules are attracted to charged poles.
Polarity of water molecules cause them to form hydrogen bonds
Hydrogen bonds:
Weak attractions between two polar molecules
Water is cohesive (sticks together) due to hydrogen bonds.
Water resists temperature change (high specific heat= more energy required to raise its temperature.) Due to extra energy required to break hydrogen bonds.