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Essential Chemistry
CE4000
All living organisms are composed of chemicals. To understand life, we must understand the structure, function,
and properties of these chemicals.
The smallest fundamental units of matter are called atoms.
Matter that is made up of the same type of atoms is called an element. There are 92 naturally occurring elements.
However, only a few of them are biologically important.
96% of the human body is composed of 4 elements; oxygen (65%), carbon (18.5%), Hydrogen (9.5%), Nitrogen
(3.2%).
The other 4% include the elements calcium, phosphorous, potassium, sulfur, sodium, chlorine, magnesium, iodine,
and iron.
Element
Abbv
H
C
O
P
N
S
K
I
Ca
Element Name
Functions
hydrogen
carbon
oxygen
phosphorus
nitrogen
sulfur
potassium
iodine
calcium
component of water and most other compounds in body
found in all organic compounds
essential for respiration; component of water and other compounds
found in bones, teeth, DNA, RNA, and ATP (energy)
found in proteins, DNA, RNA, and other organic compounds
found in many proteins
nerve impuses, muscle contractions
component of thyroid hormones (regulate metabolism)
found in bones and teeth; important for nerve impulses, muscle
contraction, and blood clotting
needed for oxygen transport and energy capture
important for membrane function, nerve impulses, and muscle
contraction
important for membrane function, and water absorption
cofactor for several enzymes
Fe
Na
iron
sodium
Cl
Mg
chlorine
magnesium
The specific characteristics and reactivity of each element is derived from the number of protons, neutrons, and
electrons that make up each atom.
Atom structure
Nucleus: central part of the atom which contains closely packed Protons which have a positive electrical charge
and Neutrons which lack an electrical charge.
Orbital: Electrons have a negative charge and orbit the nucleus of the atom, continually moving around the nucleus.
The volume of space where there is a 90% chance of finding a particular electron is called its orbital.
Each Orbital holds a maximum of 2 electrons each and come in a variety of shapes, which are represented by
probability clouds. Several orbitals may be the same average distance from the nucleus and thus contain electrons of
the same energy. Such electrons are said to occupy the same energy level or shell.
The number of electrons in an atom determine its chemical reactivity. Chemical reactivity is a function of an atom’s
valence shell - the outermost energy level or that portion of it containing chemically reactive electrons. The valence
of an atom is its combining capacity, the number of extra or deficient electrons in the outermost shell. This can be
determined by using the rule of eights - Except for the 1st shell, which is filled with two electrons, all atoms tend to
interact is such a way that they will have 8 electrons in their valence shell.
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Element: a substance composed of only one type of atom (all the atoms have the same number of protons). The
atoms may occur signally, or they may be joined to form molecules. The smallest unit of an element that retains the
properties of the element is an atom. e.g. hydrogen
Molecule: a unit composed of two or more atoms joined together by chemical bonds:
Molecular formula or chemical formula: tells us what types of atoms and how many of each are joined together.
Structural formula: shows us the actual arrangement of the atoms.
Compound: a substance composed of 2 or more elements that have been joined by chemical bonds. The smallest
unit of a compound that retains the properties of the compound is a molecule. e.g. water
Mixture: a combination of 2 or more substances that do NOT chemically combine and retain their individual
properties. e.g. sugar mixed with salt
Atoms join together in ways that give each atom a stable outer shell of electrons: If the first shell is the outer shell, it
is stable with 2 electrons. If any other shell is the outer shell, it is stable with 8 electrons.
How can an atom obtain a stable outer shell of electrons if it doesn’t already have one?
Gain electrons
Lose electrons
Share electrons
TYPES OF MOLECULAR BONDS
Ionic bond - Atoms gaining or losing electrons resulting in a positive/negative attraction. If an atom loses or gains
one or more electrons, it becomes positively or negatively charged and is then called an ion (an atom with a charge)
or an electrolyte.
Atoms lose or gain electrons when another atom of the right kind is nearby to accept or donate electrons.
Because one loses and one gains, both become ionized. Depending on the surroundings, the 2 ions go their separate
ways or stay together through the attraction of opposite charges.
Covalent bond - atoms sharing 1 or more pairs of electrons in their outer shells. Sometimes an attraction between 2
atoms is almost, but not quite enough for 1 atom to pull electrons away from the other atom. Thus, the atoms end up
sharing electrons and this is how both atoms fill their outermost shells. When have 2 atoms sharing a pair of
electrons then a covalent body is formed. Covalent bonds are stronger than ionic bonds, i.e. it takes more energy to
break the bonds.
Hydrogen bond - The weak attraction between a covalently bound H atom with a slight positive charge and
another covalently bound atom with a slight negative charge. May occur between different molecules or between
different parts of the same molecule due to polarity
CHEMICAL REACTIONS
Atoms and molecules are in constant motion; either vibrating (solids) or moving freely and randomly (fluids).
Sometimes they collide with one another and interact by undergoing chemical reactions. The rate at which atoms
collide and react with each other depends on the following factors
1. concentration
2. speed
3. energy (energy of activation)
4. orientation
Chemical reactions take place whenever chemical bonds are formed, rearranged, or broken. There are four basic
types of reactions that can occur.
1. Synthesis reactions- atoms or molecules combine to form a product
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2. Decomposition reactions - molecules breakdown into smaller molecules or atoms
3. Exchange reactions - molecules exchange constituent components (swap partners)
4. Reversible reactions - the product of a previous reaction can revert to the original reactants.
Often, the products of chemical reactions form compounds. Compounds can be classified as either inorganic
compounds and organic compounds.
Important inorganic molecules include water, oxygen, carbon dioxide, and many salts, acids, and bases.
ORGANIC CHEMISTRY
Inorganic molecules: Relatively small, simple molecules that usually lack C (a few have one C atom). Examples:
CO2, NH3, H2O, O2, H2
Organic chemistry is the science of molecular compounds involving carbon. All organic compounds contain
carbon, but many also contain hydrogen, oxygen, nitrogen, sulfur, phosphorus, salts, and other elements.
Organic molecules are large, complex molecules whose structure is based on a backbone of C atoms (always contain
C as a major part of their structure). Examples: C6H12O6, C2H5COOH
Living organisms are composed of both inorganic and organic molecules
Carbon has an atomic # of 6. How many valence electrons does it have? nCarbon can form 4 strong covalent bonds
with up to 4 other atoms. Carbon atoms can form strong covalent bonds with each other to produce unbranched
chains, branched chains, and rings.
Versatility:
- Carbon rings can join with each other to form interlocking rings or chains of rings.
- Carbon can form single, double, or triple covalent bonds with other atoms.
- Isomers are molecules that have the same molecular formula (same number and type of atoms) but which have
different properties because the atoms are arranged differently.
Organic compounds are specifically those carbon compounds in which the principle bonds are carbon-to-carbon
and carbon-to-hydrogen.
Functional groups are specific groups of atoms that are responsible for most of the characteristic chemical
properties of an organic compound, examples include:
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