Download The Nature of Molecules

The Nature of Molecules
Our study of life begins with
physics and chemistry – as life,
itself, is a chemical machine
1st, some definitions
• Matter = any substance having mass and which takes up
space; all matter is composed of atoms
• Atoms = the simplest/smallest component of matter;
composed of nucleus and electron orbital(s)
– # of protons = Atomic number
– # of protons + neutrons = Atomic mass
• Naturally-occurring atoms on Earth = 90
• Diagram of typical atomic structure:
• Atomic #/mass of: H, He, C, O, N, S, P, Ne
Fig. 2.2.a
Isotopes
• All atoms of an element contain the same
number of protons, but not the same number of
neutrons
• Atoms possessing different numbers of neutrons
are isotopes
– Ex: Carbon has 3 isotopes (99% have 6 neut’s) =
12C
there is also 13C and 14C (14C is a radioactive isotope with a
half-life of 5730 years)
• Isotopes are commonly used in research and in
medicine
Fig. 2.3
Electrons
• Negatively charged particle(s) which orbit
the nucleus
• Electrons may be lost or gained from one
atom to another to form a charged atom or
ion….e.g., Na + Cl (formation of
cation/anion)
• # of electrons determines the behavior,
hence chemical activity of an atom
Fig. 2.4
Electrons and energy levels
• There are discrete energy levels surrounding the
nucleus of an atom; one level contains only 1
orbit of electrons, others contain 4 different
orbits of electrons (each orbit is filled with 2 e-’s)
• The filling of orbitals and energy levels relates to
the chemical behavior of atoms
• The number of electrons of an atom relates to its
valence
• Valence relates to how one atom reacts with
another
Fig. 2.7
Fig. 2.5
***Inner energy shells (those closest to the
nucleus) contain electrons with lower energy
than the outer energy shells
***important concept as it will be
discussed in the Light Dependent reaction of
Photosynthesis
The elements of biology
• The large biomolecules which comprise
life are composed, primarily, of 6
elements: CHONPS (98.9%) = all having
low atomic masses….check it out……
• Examples of biomolecules:
• These elements contain valences that
dictate how they react with other atoms of
elements => through covalent bonds.
Chemical bonding
• Bonding occurs between interacting atoms
in several ways; mainly through:
– loss/gain of electron from one atom to
another = Ionic bonding (found in salts and
other crystalline molecules)
Or
-sharing of electrons between atoms = covalent
bonding (found in biomolecules)
Fig. 2.8.a
Ionic bonding of NaCl (Sodium chloride)
Sodium (Na) losses an e- and Chlorine (Cl) gains an e-; hence
charged atoms (ions) form and are attracted to one another
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Covalent bonding of some common gases
Lastly, some definitions:
• A group of at least 2 atoms joined together
by a chemical bond is called a molecule
• A molecule that contains more than one
element is called a compound