1. The Chemical Basis of Life
Chapter 2

2. Matter Substance that has mass and takes up space
Compose all living things
Generally found in 1 of 3 states
Composed of 1 or more elements

3. Elements 92 occur naturally on Earth
4 make up 96% of the human body (CHON)
Composed of atoms

4. Atoms Smallest particles that retains properties of an element
Made up of subatomic particles:
Protons (+) in nucleus
Electrons (-) orbits nucleus
Neutrons (no charge) in nucleus
Protons and neutrons
Mass of about 1
Electrons
Mass is negligible (1/2000)

5. Reading A Periodic Table
Elements differ depending on the number of subatomic particles
Atomic symbol
1st letter or 2 (usually)
Atomic number
Determined by number of protons
Element specific
Mass number
Determined by number of protons + neutrons

6. Isotopes Atoms with different number of neutrons
Effects mass number how?
Effects atomic number how?
Can be stable or unstable (radioactive)
Behave the same as respective element (electrons are key)
Occur naturally as a mix in elements
Living cells can’t distinguish between them
Applications
Dating fossils
Biological tracers
Brain scanning
Cancer treatments
Dangers
Radioactive atoms give off energy that destroys chemical bonds when they collide

7. Chemical Properties of Atoms
Electrons are key
Move in orbitals called shells
Repel one another, but attracted to protons
Electron shells
Outermost determines chemical properties
Closer to the nucleus = lower energy and are filled first
Holds up to 2 or 8 electrons
Filled are unreactive
Unfilled are reactive
Number differs between atoms

8. Electron Shell Models HYDROGEN 1p+ , 1e- HELIUM 2p+ , 2e- CARBON
OXYGEN
8p+ , 8e-
SODIUM
11p+ , 11e-
CHLORINE
17p+ , 17e-
NEON
10p+ , 10e-
electron
proton
neutron

9. Chemical Bonds Hold 2 or more atoms together
Complete outer shells
By sharing, donating, or receiving electrons
Form molecules (H2, I2, and O2) or compounds (H20, NaCl, C6H12O6)
Demonstrates emergent properties
2 H+ (gas) + O- (gas) = H2O (water)
Na+ (metal) + Cl- (poisonous gas) = NaCl (table salt)

10. Ionic Bond One atom loses electrons  cation (charge?)
Another atom gains these electrons  anion (charge?)
Charge difference attracts the two
Very weak bond
Table salt (NaCl)
cation anion

11. Covalent Bond Atoms share outer pair or pairs of valence electrons
Single, double, or triple covalent bond
Non-polar covalent
Electrons shared equally
E.g.: hydrogen gas/ H2/ H-H
Polar covalent
Electrons spend more time near most electronegative nucleus
E.g.: water/ H20
electrons more attracted to O nucleus than to either H nuclei

12. Hydrogen Bond
Positive charge on H attracts negative charge on another atom
Individually weak, but often numerous = strong
Important to many biological compounds
E.g. water
Makes up 70 – 90% of all living things
Bonds create unique properties

13. Properties of Water Solubility Polarity Solvent: dissolving agent
Solute: substance that is dissolved
Solution: liquid mix of 2+ substances
Aqueous solution when water is solvent
Polarity
‘Like dissolves like’
Hydrophilic
Sugar or salt and water
Hydrophobic
Oil and water

14. Properties of Water (cont.)
Water movement
Cohesion
Creates surface tension
Overfilling a glass, a ‘belly flop’, or beading of water
Adhesion
Water moves up plants against gravity or paper towels
Temperature stabilization
Molecule mov’t affects temp
Hard to change H-bonds
Increase  ice formation
Reduce  evaporation
Vary  internal temp.

15. 0---------------------7-------------------14
pH Scale
Measures [H+] of a solution (acidity)
Change of 1 on scale means 10X change in [H+] (logarithmic scale)
Highest H Lowest H+
Acidic Neutral Basic

16. pH Scale (cont.) Acids Bases Neutrals Increase [H+] pH less than 7
Decrease [OH-]
pH greater than 7
Neutrals
Equal [H+] and [OH-]
pH of 7.0

17. Buffer Systems Minimize shifts in pH
Can accept H+ when in excess and donate H+ when depleted
Form water
Common in biological fluids
Human blood at 7.4, slight deviations can be deadly

18. Making and Breaking Bonds
Chemical reactions are often reversible
Chemical equilibrium: forward and reverse reactions occurring at the same rate (no net change)
Starting materials are reactants, ending are products
# of atoms are conserved
1st law of thermodynamics
Label the parts of this reaction