1. The Chemistry of Life

2. Why are we studying chemistry?
Chemistry is _______________________

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

4. Different kinds of atoms = elements
The World of Elements H C N O Na Mg P S K Ca
Different kinds of atoms = elements

5. Life requires ~25 chemical elements
About 25 elements are essential for life
Four elements make up 96% of living matter:
• __________ • hydrogen (H)
• oxygen (O) • ___________
Four elements make up most of remaining ____:
• phosphorus (P) • calcium (Ca)
•__________ • potassium (K)

6. How does this atom behave?
Bonding properties
Effect of electrons
electrons determine chemical behavior of atom
depends on number of electrons in atom’s outermost shell
_______________
How does this atom behave?

7. Bonding properties Effect of electrons
What’s the magic number?
Bonding properties
Effect of electrons
________________________________________________________________________
Sulfur on the LEFT
Magnesium on the RIGHT
How does this atom behave?
How does this atom behave?

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

9. Elements & their valence shells
Elements in the same column have the same valence & similar chemical properties
Remember
some food chains are 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

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

11. Bonds in Biology Weak bonds Strong bonds Hydrogen bond
H2O
Weak bonds
___________________
attraction between + and –
hydrophobic & hydrophilic interactions
interaction with H2O
________________
(ionic)
Strong bonds
covalent bonds
H2O
Covalent bond –
H2 (hydrogen gas)

12. Covalent bonds Why are covalent bonds strong bonds? Forms molecules
_______________________________
both atoms holding onto the electrons
very stable
Forms molecules H
Oxygen – H O
H — H
H2 (hydrogen gas)
H2O (water)

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

14. Nonpolar covalent bond
Pair of electrons _____________by 2 atoms
example: hydrocarbons = CxHx
methane (CH4 )
balanced, stable, good building block

15. Polar covalent bonds Pair of electrons ____________by 2 atoms
example: water = H2O
oxygen has stronger “attraction” for the electrons than hydrogen
oxygen has higher ________________
water is a _____________
+ vs – poles
leads to many interesting properties of water… H
Oxygen + – – – – +

16. Let’s go to the videotape!
Hydrogen bonding
Polar water creates molecular attractions
attraction between positive H in one H2O molecule to negative O in another H2O
also can occur wherever an -OH exists in a larger molecule
_____________ H H O
Let’s go to the videotape!