Chapter 2- Water and Carbon: The Chemical Basis of Life
Chemical evolution: Early in earth’s history, simple chemical compounds in the atmosphere and
ocean combined to form larger more complex substances.
2.1 Building Blocks of Chemical Evolution
H, C, N, O make up 96 percent of all matter found in organisms today.
-atomic number: protons. Subscript of each element
-isotopes: forms of an element with different numbers of neutrons.
-mass number: protons plus neutrons
-orbital: electrons move around nuclei in specific regions. 2 electrons. Grouped into electron
-valence: number of unpaired electrons in an atom.
-Atom is most stable when valence shell is filled.
-covalent bonds: share electrons; form molecules.
-nonpolar covalent bond: equal sharing of electrons. Symmetrical
-polar covalent bonds: asymmetric sharing of electrons. Some atoms hold electrons in covalent
bonds much more tightly than do other atoms—electronegativity.
Electronegativities: O >> N > C= H
Ionic bonds: electrons transferred. Gives resulting atom full shell. Cation- loses electron.Anion-
-Mass of one mole of any molecule is the same as its molecular weight expressed in grams.
Molecular weight is the sum of the mass numbers of all elements in a molecule.
-Molarity is the number of moles of the substance present per litre of solution
-Water is polar meaning the overall distribution of charge is asymmetrical.
-ions and polar molecules are hydrophilic. Uncharged and nonpolar are hydrophobic.
-Hydrogen bonding makes it possible for almost any charged or polar molecule to dissolve in
-Properties of water
1. forms hydrogen bonds
2. solvent 3. cohesion- binding between like molecules. Water stays together because of hydrogen bonds
between the molecules.
4. adhesion- Binding between unlike molecules. Water adheres to surfaces that have any polar or
5. surface tension- any force that depresses