Chapter 2
The Chemical Level of Organization
Everything on our planet is made of atoms and molecules.
Two important generalizations:
1. Even though living things are diverse; their chemical composition and
metabolic processes are similar.
e.g. this is why studying bacteria and rats can be beneficial to studying
humans.
2. The physical and chemical principles governing living systems are the same
as those governing non-living systems.
e.g. carbon atoms act the same way (have the same physical properties) in
both humans and piece of paper.
Chemistry – the science of the structure and interaction of matter.
- All things are made up of matter.
Matter – occupies space and has weight or mass.
Mass – the amount of matter in any given object that does not change or is invariable.
Weight – the force of gravity acting on matter.
- weight is variable or changing
Chemical Elements
States of Matter – matter exists in three states: 1. Solid – have definite shape and
volume.
e.g. teeth and bones
2. Liquid – have definite volume but
takes on shape of container.
e.g. blood plasma
3. Gas – have neither a definite shape nor
volume and fill their container.
e.g. air
Samples of Matter:
Steam (G)
Blood (L)
Sand (S)
Water (L)
Mercury (L)
Aspirin (S)
Ice (S)
Oxygen (G)
Carbon Dioxide (G)
Alcohol (L)
Note: H2O can exist in all three.
Elements – are substances that cannot be broken down into simpler substances by
ordinary chemical reactions.
- there are approximately 115 elements
- 92 occur naturally
- the others form as a by-product of forced reaction.
e.g. nuclear reactor waste (plutonium); or particle acceleration
- approximately 98% of an organism’s mass is composed of just sic or 7
elements: CHONPSCa
Whatever physical state matter may assume – gas, liquid, or solid – it is composed of
units called atoms.
Atoms – the smallest portion of an element that retains its chemical properties.
Structure of the atom: the nucleus (center of atom) contains subatomic particles protons
and neutrons.
- each proton has a positive charge of (+1)
- neutrons are uncharged particles with about the same mass as
protons.
- protons and neutrons makeup almost all of the mass of an atom.
protons + neutrons = atomic mass (atomic mass units –amu)
- because of the fixed number of protons (invariable) the atom
is identified by the number of protons.
protons = atomic number
the shell (surrounding center of atom) the space outside the
nucleus contains the electrons.
- each electron carries a negative charge of (-1)
protons + electrons = the charge of the atom
- electrons are attracted by the positive charge of the protons
- the atoms of each type of element have a characteristic number of
electrons around the nucleus – the number can change during
chemical reactions.
- when the number of protons equals the number of electrons the
atom is neutral – no net charge.
Isotopes – elements that have different numbers of neutrons and thus different masses.
- isotopes of the same element have the same number of protons and
electrons but neutrons vary.
e.g. Hydrogen (H) has three isotopes: 1H (0 neutrons)
2
H (1 neutron)
3
H (2 neutrons)
- all three have the same chemical characteristics, but mass is different.
- some isotopes with an excess of neutrons are unstable and tend to break
down, or decay, to a more stable isotope.
- radioisotopes (radioactive) useful in research, cancer treatments,
and medical diagnosis.
e.g. C12 (most common)
C13
C14 (radioactive – unstable)
- radiation can also be deadly.
e.g. Chernobyl (nuclear power plant meltdown)
X-Rays (dentist office)
Sun Exposure
Periodic Table- A summary of chemical properties of different kinds of matter.
- elements are arranged in order of increasing atomic number (number of
protons). rows of the table are called periods.
- elements are also arranged in vertical columns called groups or
families. They are usually numbered by Roman Numerals and often
indicate the number of electrons in the outermost shell (ring) as well as
react similarly.
Ions, Molecules, and Compounds
Ions – atoms that have a charge (+) or (-)
- ions are the result of an ionic reaction; electrons have been lost or gained
(Ionization).
- cations – atoms with positive charge.
e.g. Ca++, K+, Na+, Mg++, Fe2+, Fe3+
anion – atoms with negative charge.
e.g. Cl-, IMolecules – two or more atoms united by a covalent chemical bond. They may be likeatoms (e.g. O2, N2) or different atoms (e.g. C6H12O6)
Compounds – formed when two or more elements are chemically combined in a fixed
ratio. e.g. H2O, NaCl, KI, CaCl
- a chemical change has occurred and the combining elements disappear and
a new substance with entirely different properties appear.
e.g. O and H alone are gases but though chemical reaction a liquid
is formed.
Note: H2O is unique – it is a molecule because it consists of 2 types of atoms
it is a compound because it has gone through a chemical change.
Mixtures – physical combinations of two or more elements, or elements and compounds,
or of two or more compounds.
e.g. a cup of coffee
Free Radicals – atoms that have 1 electron (unpaired) in its outermost shell or bonded
atoms that have 1 lone unpaired electron.
- causes instability
- destroys other molecules in the body by taking electrons.
e.g. superoxide - two bonded oxygen molecules with 1 unpaired
electron.
Bonds - atoms are joined by their electrons to form larger and more complex molecules.
3 Types of Bonds:
1. Ionic Bonds
2. Covalent Bonds
3. Hydrogen Bonds
Ionic Bonds – form when one atom donates or accepts electrons.
- the end result is an ion (ionization).
- ionic compounds exist in the body as electrolytes.
electrolytes – ions that form in solution.
e.g. bones and teeth are made stronger
The Movement of electrons is important in Ionic Bonds:
Electron Donors (cations) – atoms with fewer electrons in the outermost
ring will donate its electrons to another atom
and become an ion (cation).
e.g. Na becomes a cation Na+
Electron Acceptor (anion) – atoms with more electrons in the outermost
ring will accept electrons to become an ion
(anion).
e.g. Cl becomes an anion Cl-
Ionic Bonding between 2 or more atoms occurs due to charge of atoms –
opposites attract.
e.g. Na+ bonded to Cl- becomes NaCl
Covalent Bonds – strong, stable bonds formed when atoms share electrons.
- more complex molecules are formed.
e.g. Cl + Cl become Cl-Cl or Cl2 (chlorine gas)
Important Atoms in Living Systems and Their Bonding Requirements
Carbon (4 electrons) - requires 4 bonds
Hydrogen (1 electron) - requires 1 bond
Nitrogen (5 electrons) - requires 3 bonds
Oxygen (6 electrons) - requires 2 bonds
-atoms can have more than one bond:
Single Bonds – 2 atoms share 1 pair of electrons
Double Bonds – 2 atoms share 2 pairs of electrons
Triple Bonds – 2 atoms share 3 pairs of electrons
-covalent bonding also occurs between non-like atoms.
e.g. CH4 and H2O
Polar and Non-Polar Covalent Bonds
Covalent bonds are non-polar if the electrons are shared equally
between the two atoms.
e.g. Cl-Cl
Covalent bonds are polar if one atom has a greater affinity for
electrons than the other atom(s).
- the atom with the greater number of protons has the
greatest affinity for electrons – electronegativity.
- one or both molecules will have a partial charge.
δ=delta (partial charge) - δ- or δ+
e.g. in H2O Oxygen has a greater affinity for the electrons
of hydrogen. This causes oxygen to have a partial (-)
charge and the hydrogens to have a partial (+) charge.
Hydrogen Bonds – are relatively weak bonds formed when a hydrogen
atom in one molecule is attached to a highly electronegative element in another molecule or in another part
of the same molecule.
e.g. O or N (highly electronegative)
- another molecule: between 2 water
molecules.
- within same molecule: a water molecule or
an ammonia molecule.
- very important property in water.