CHEMISTRY REVIEW NOTES
I. ATOMIC LEVEL
A. Atom
1. Definition - smallest unit of an element that retains all of the element's properties
2. Structure
a. protons (+) - nucleus
b. neutrons - nucleus
c. electrons (-) - outside nucleus, in orbitals
B. Changes in...
1. # of neutrons - is then called an isotopes
- often radioactive
2. # of electrons - this is the most common change
- are then called ions
C. Stability of the atom
1. valence - # of electrons an atom must share, lose, or gain to complete a stable outer electron shell
2. to become more stable, all atoms try to complete the number of electrons in their outer orbitals
3. to become more stable, atoms interact with other atoms
a. through sharing electrons, taking electrons away from, or giving electrons to other atoms
b. this interaction is called bonding
II. BONDS
A. General information
1. Strength of a bond is measured in terms of the energy required to break it/form it
2. Three kinds - ionic, covalent, hydrogen
B. Ionic – Definition = loss and gain of electrons to create charged particles called ions
1. Example: NaCl
2. is caused by electrostatic attractions between 2 ions (one is +, the other is -)
3. is soluble (will dissolve) in water
4. is polar (see description below)
5. one end of the molecule is positive, and the other end is negative
C. Covalent
1. Definition - sharing of electron pairs between two or more atoms
2. Two kinds - nonpolar and polar
a.. Nonpolar - the average position of electron is about midway between the two atomic nuclei;
equal sharing of electron pairs
1). Example: F2
2). is insoluble in water
3) Is important in organic systems - chains of covalent bonds create organic molecule of life
4) It causes the molecule to have no charge
b. Polar - unequal sharing of electron pairs
1). is caused by electronegativity (how strongly an atom attracts electron) - one atom
attracts the electron more strongly than the other atom
2). Example: H20
CHEMISTRY REVIEW, P. 2
3). Example: HCl
4). this type of bond is able to share more electron for longer period than nonpolar - is
stronger
5) One end of the molecule has a partial positive charge, and the other end a partial
negative charge
6) is soluble in water
D. Hydrogen
1. weak and often transient electrical attraction between 2 atoms bearing partial electrical charges
2. example = the attraction between a hydrogen of one water molecule and the oxygen of another water
molecule
E. Van der Waals Interactions
1. Electrons temporarily concentrated in one end of the molecule
2. Temporary charged region
3. Very weak – only work when molecules are very close
F. Weak Bonds are important to life because they give cells the opportunity to pass substances between them
G. Importance of Shape
1. Many molecules are 3-dimensional and/or angular
2. They must have an EXACT shape, or they can’t perform their function
3. Think “Lock and Key”
4. Form follows function – they are a certain shape because they have a certain function
III. COMPOUNDS AND MOLECULES
A. Molecule - 2 or more elements held together by covalent or ionic bonds
Compound - made of molecules composed of 2 or more different kinds of atoms in definite proportions
B. Molecular formula - shows types and # of atoms
1. example- C6H12O6
2. example- H20
3. example- NaCl
4. example- CO2
C. Structural formula - shows physical arrangement
1. example2. exampleE. Solutions
1. Def'n - compound dissolved in water
2. solute - substance that is dissolved
3. solvent - does dissolving, what solutes are dissolved in
IV. CHEMICAL REACTIONS
A. Energy dependent
1. Endothermic - energy must be added to the reaction
2. Exothermic - releases energy
B. Three major types of reactions
1. combination reaction
CO2 + H2O
H2CO3
2. dissociation reaction
NaCl
Na+ + Cl3. exchange reaction
AgNO3 + NaCl
AgCl + NaNO3
CHEMISTRY REVIEW, P. 3
V. Importance of pH
A. Important because nearly all of life’s chemistry occurs near pH 7 (usually 7.3-7.5)
B. Acid - substance that releases H+ when it dissociates in H2O ; has a pH lower than 7
Example –gastric fluid, HCl, lemon juice
C. Base - (alkali) substance that releases OH- in H2O or accepts H+ ; has a pH higher than 7
Example – NaOH, egg white, sea water
D. Buffer - substances that tend to keep the pH constant by taking up or releasing H+ or OH1. Excess H+ or OH- can alter how biological molecules function
2. Examples:
a. Your body could have excess H+ because of not breathing, having diarrhea, drinking acidic.
In this case, in your cells, the bicarbonate ion (HCO3) acts as a buffer by bonding with
the H+. This then becomes carbonic acid.
H+ + HCO3H2CO3
b. Your body could have excess OH- because of vomiting, fast breathing, or exercise.
In this case, in your cells, carbonic acid (H2CO3) acts as a buffer, bonding with
the excess OH-, becoming water and bicarbonate
OH- + H2CO3
H2O + HCO3
E. Salt
1. Definitions
a. any compound that dissolves easily in H2O and releases ions OTHER THAN H+ or OHb. substance in which the H+ of an acid has been replaced by other positively charged ions
2. Example - NaCl