1. The Chemical Context of Life
Chapter 2:
The Chemical Context of Life

2. Chemical Context of Life
Matter (has volume & mass)
Element; compound
The atom
Atomic number (proton #); mass number (protons + neutron)
Isotopes (different # of neutrons); radioactive isotopes (nuclear decay)
Energy (ability to do work); energy levels (electron states of potential energy)

3. Chemical Bonding Covalent Double covalent Nonpolar covalent
Ionic
Hydrogen
van der Waals

4. Covalent Bonding Sharing pair of valence electrons
Number of electrons needed to complete an atom’s valence shell determines how many bonds will form
Ex: Hydrogen & oxygen bonding in water; methane

6. Polar/nonpolar covalent bonds
Electronegativity: attraction for electrons
Nonpolar covalent
electrons shared equally
Ex: diatomic H (H2) and O (O2)
Polar covalent
1 atom more electronegative than other(s)
Creates partial charges
Ex: water

7. Polar/nonpolar bonds

8. Ionic bonding
High electronegativity difference strips valence electrons away from another atom
Electron transfer creates ions (charged atoms)
Cation (positive ion); anion (negative ion)
Ex: Salts (sodium chloride)

9. Hydrogen bonds
H atom is covalently bonded to 1 electronegative atom (N,O,F)
It is also attracted to an electronegative atom (N, O, F) on a separate molecule
Is not a real bond, is an intermolecular attraction (weaker than bond)

11. van der Waals interactions
Weak interactions between molecules or parts of molecules
Due to localized charge fluctuations
Caused by electrons constant motion
At any given instant, ever-changing “hot spots” of negative or positive charge may develop from electron’s locations