1. PowerPoint by Kim Foglia Division High School Levittown, NY Modified by Kathleen Crawford Science Hill High School Johnson City, TN

2. The Chemistry of Life Domains of Study Domain of BioMolecules
Domain of Cells
Domain of Organisms
Domain of Populations
Domain of Communities
IB Biology

3. I. Why are we studying chemistry?
Chemistry is the foundation of biology.

4. Everything is made of matter Matter is made of atoms
Hydrogen
1 proton
1 electron
Oxygen
8 protons
8 neutrons
8 electrons
Proton +
Neutron
Electron –

5. The World of Elements Different kinds of atoms =different elements H CNa Mg P S K Ca
Different kinds of atoms =different elements

6. II. About 25 elements are essential for life
Four elements make up 96% of living matter:
• carbon (C) • hydrogen (H)
• oxygen (O) • nitrogen (N)
III. Five additional elements are important in living things:
• phosphorus (P) • calcium (Ca)
• sulfur (S) • iron (Fe)
sodium (Na)

7. IV. Role of some elements in living things:
Sulfur – Used in some amino acids
Calcium – Found in bones/teeth
Iron – Found in haemoglobin (hemoglobin) in animals
Sodium – Needed for a nerve impulse
Phosphorus – Found in cell membrane
structures

8. V. Bonding properties Effect of electrons
Electrons determine chemical behavior of an atom.
Depends on number of electrons in atom’s outermost shell
or energy level.
Valence shell is another
name for outer shell.
How does this atom behave?

9. Bonding properties Effect of electrons
What’s the magic number?
Bonding properties
Effect of electrons
Atoms are stable when outer shell is full or has 8 electrons (Octet rule)
Sulfur on the LEFT
Magnesium on the RIGHT
How does this atom behave?
How does this atom behave?

10. VI. Elements & their valence shells
Elements in the same row have the same number of energy levels.
Moving from left to right, each element has a sequential addition of electrons (and protons)

11. Elements & their valence shells
Elements in the same column have the same valence and similar chemical properties
Remember
some food chains were built on reducing O to H2O
& some on
reducing S to H2S
Oxygen has medium electronegativity so doesn’t pull electrons all the way off hydrogen whereas chlorine would.
So oxygen forms a polar covalent bond.
Carbon has only a weak electronegativity so forms a nonpolar covalent bond

12. VII. Chemical reactivity
Atoms tend to
complete a partially filled valence shell or
empty a partially filled valence shell
This tendency drives chemical reactions…
and creates chemical bonds – –

13. Weak bonds Strong bonds VIII. Bonds in Biology Hydrogen bond
H2O
Weak bonds
hydrogen bonds
attraction between + and –
hydrophobic & hydrophilic interactions
van derWaals forces
ionic bonds (sometimes weak)
Strong bonds
covalent bonds- share electrons
ionic bonds - transfer electrons;
(sometimes strong)

14. Covalent bonds Why is this a strong bond? Forms molecules
Two atoms share a pair of electrons
Both atoms holding onto the electrons
Very stable
Forms molecules H
Oxygen – H O
H — H
H2 (hydrogen gas)
H2O (water)

15. Multiple covalent bonds
2 atoms can share >1 pair of electrons
double bonds
2 pairs of electrons
triple bonds
3 pairs of electrons
Very strong bonds
More is better! H
H–C–H –

16. Polar covalent bonds Pair of electrons shared unequally by 2 atoms
Water = O + H
Oxygen has stronger “attraction” for the electrons than hydrogen
Oxygen has high electronegativity
Water is a polar molecule
“+” and “–” poles
Leads to many interesting properties of water… + – H
Oxygen – – – +

17. Hydrogen bonding Polar water creates molecular attractions Weak bond
Positive H atom in one water molecule is attracted to negative O in another water molecule.
Also can occur wherever an -OH exists in a larger molecule.
Weak bond
Typical strength of 5.0
kcal/mol, but it varies.
APBio/TOPICS/Biochemistry/MoviesAP/03_02WaterStructure_A.swf
Weak bonds are still
important!

18. Oxygen – Significantly larger nucleus
Greater charge (+8)
Hydrogen – Smaller nucleus
Charge of (+1)
Electron pair found closer to the oxygen nucleus than the hydrogen nucleus.
Oxygen carries a small negative dipole,
and hydrogen carries a small positive dipole.