Ch. 2 Notes
Mr. Lesar
Fall ‘14
Name ________________
2-1 and 2.2: The Chemistry of Life
Atom – The basic unit of matter
 Protons
(p+)
positively charged particles which are located in the nucleus.
STRONG FORCES BIND THESE TWO TOGETHER
TO MAKE UP THE NUCLEUS
PROTONS + NEUTRONS = ATOMIC MASS UNIT
# PROTONS = ATOMIC MASS NUMBER


Neutrons
Electrons
(no)
(e-)
neutrons carry no charge but are located in the nucleus.
electrons carry a negative charge and are in constant
motion in the space surrounding the nucleus.
Element – A pure substance that consists entirely of one type of atom. Elements are represented
by a one-or two-letter symbol.
Isotopes – Atom of an element that has a number of neutrons different from that of other atoms
of the same element.
Compounds – A substance formed by the chemical combination of two or more elements in
definite proportions. H2O CO2
C6H12O6



Water - H2O – is composed of 2 hydrogen atoms and 1 oxygen atom
Carbon dioxide - CO2 – Is composed of one carbon atom and 2 oxygen atoms
Glucose - C6H12O6 - Is composed of 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen
atoms.
Chemical Bonds

Ionic bonds are formed when one or more electrons are transferred from one atom to
another.
Covalent Bonds are formed when electrons are shared between atoms.
o
Molecules – The structure that results when atoms are joined together by covalent
bonds is called a molecule. A molecule is the smallest unit of most compounds.
2-2 Properties of water
1. Like all molecules, a water molecule, H2O is neutral. The positive charges on its 10
protons balance out the negative charges on its 10 electrons.
2. With 8 protons in its nucleus, an oxygen atom has a much stronger attraction for
electrons that does the hydrogen atom with a single proton in its nucleus.
a. Thus at any given moment there is a greater probability of finding the shared
electrons near the oxygen atom than near the hydrogen atom.
i.
As a result, the oxygen end of the molecule has slight negative
charge and the hydrogen end of the molecule has a slight positive
charge.
ii.
A molecule in which the charges are unevenly distributed is called a
polar molecule.
iii.
Hydrogen Bonds: Because of their partial positive and negative
charges, polar molecules can attract each other. The attraction between
the hydrogen atom on one water molecule and the oxygen atom on
another water molecule is an example of a hydrogen bond.
iv.
Cohesion: The attraction between molecules of the same substance.
Water is an example
v.
Adhesion: The attraction between molecules of different substances.
Water and a graduated cylinder – the meniscus.
vi.
Mixture: A material composed of two or more elements or compounds
that are physically mixed together but not chemically combined.
1. Homogeneous: A mixture that is the same throughout. Think of
milk.
2. Heterogeneous: A mixture that is not the same throughout. Oil
and water.
Solution: A mixture of two or more substances in which the components are evenly distributed throughout
the solution
Solute: The substance that is dissolved.
Solvent: The substance in which the solute dissolves.
Suspensions: Mixtures of water and non-dissolved materials.
Acids Bases and pH
The pH scale:
 The pH scale indicates the concentration of H + ions in solution.
 The scale ranges from 0-14.
 At a pH of 7 a substance is said to be neutral.
 Solutions below 7 are called acidic.
 The lower the pH, the greater the acidity.
 Solutions above 7 are called basic.
 The higher the pH the more basic the solution.
 Each step on the pH scale represents a factor of 10. A solution with a pH of 4 has 10 times as
many H+ ions as a solution with a pH of 5. (Assuming equal volumes)
 Buffers are weak acids or bases that can react with strong acids or bases to prevent sharp
sudden changes in pH
Acids and acidic solutions: An acid is any compound that forms H+ ions in solution. Acidic
solutions have higher concentrations of H+ ions than pure water and have pH values below 7
Bases and basic (or alkaline) solutions: A base is a compound the produces hydroxide ions
(OH-) in solution. Basic or alkaline solutions contain lower concentrations of H+ ions then pure
water and have pH values above 7.