The Chemistry of Life
Chapter 2
2.1 Start with Atoms
• Atoms are the smallest units of an element
which still retain the unique properties of
that element
• What are the basic components that make
up an atom?
2.1 Start with Atoms
• The components of an atom are:
– Protons (p+) : Particles that have mass and
carry a positive charge.
– Neutrons (n): particles that carry mass but are
not charged
– Electrons (e-): Particles that have little mass
and carry a negative charge
Fig. 2.3, p. 22
2.1 Start with Atoms
• Each element has a unique atomic
number, or the number of protons in the
atom.
– The atomic number is what conveys the
unique properties of the atom or the element.
– Example: Every atom with 8 protons is
identified as an Oxygen atom. It behaves as
oxygen due to the chemical characteristics
bestowed upon it because of its 8 protons
2.1 Start with Atoms
• What would happen to an oxygen atom if
we were to knock 2 protons out of its
nucleus?
• Answer: it would turn into a carbon atom.
2.1 Start with Atoms
• Mass number is equal to the total number
of protons and neutrons
• Example: Oxygen with 8 protons and 8
neutrons would have a mass number of
16.
Electrons
• An atom has about the same number of
electrons as protons.
• Electrons which are negatively charged
are effected by both the positive charged
nucleus and the negative charge of other
electrons.
Electrons Cont• How do negatively charged electrons spend as
much time as possible near the nucleus and at
the same time keep far enough away from other
electrons?
• In order to stay as close to the positive charged
nucleus as possible but away from each other,
electrons travel different orbital paths or energy
levels around the nucleus
Electrons
• For Example, the
closest path near the
nucleus is small. It
can only hold two
electrons before they
start getting in each
others way.
HELIUM
2p+ , 2e-
Electrons
• The Next orbital path
is larger in
circumference and is
able to contain 8
electrons of higher
energy.
• The carbon atom
which has 6 electrons
places 2 in the inner
orbital and 4 in the
outer.
Electrons Cont• Oxygen’s atomic
number is 8. How
would Oxygen’s
electrons be
represented around
the nucleus?
Electrons Cont• Sodium has an
atomic number of 11.
How would sodium’s
electrons be
represented around
the nucleus?
Electrons Cont• Chlorine has an
atomic number of 17.
How would Chorine's
electrons be
represented around
the nucleus?
Electrons Bind Atoms together
• Atoms often are able to bind together to
form molecules.
– A molecule is a substance that has two or
more atoms bound together.
• There are two different types of molecules
– Elements are molecules that are made up of
two or more atoms, but the atoms are all of
the same type
– Compounds are molecules that are made up
of two or more different types of atoms
Molecules
•
Question?
–
H2O is a
A)
B)
C)
D)
E)
F)
Molecule
compound
Element
A molecule and a Compound
A molecule and an element
A element and a molecule
Electrons Bind Atoms together
• The Rule of 8
– Atoms want to have a full outer shell of
electrons
– Atoms are very reactive to other atoms until
they have a full outer orbital of electrons
– Atoms will barrow or steal or give away
electrons to other atoms to gain a complete
orbital
– In so doing they form bonds
Electrons Bind Atoms together
• There are three different types of bonds
– Ionic bonds
– Covalent bonds
– Hydrogen bonds
Ionic Bonds
SODIUM
ATOM
11 p+
11 e-
SODIUM
ION
11 p+
10 e-
electron transfer
CHLORINE
ATOM
17 p+
17 e-
CHLORINE
ION
17 p+
18 e-
Fig. 2.10a, p. 26
Click to view
animation.
animation
1 mm
Fig. 2.10b, p. 26
Hydrogen bonding
• Hydrogen bonding is bonding that occurs
between molecules not atoms
• Molecules that are made up of hydrogen
atoms bonded to larger atoms have a
polarity of charge.
– One side of the molecule is positively charged
and the other end is negatively charged
Hydrogen bonding Cont• The polarity of charge is
due to the fact that
electrons don’t spend as
much time around the
nucleus of hydrogen as
they do around the
nucleus of larger atoms.
• The hydrogen end of the
molecule is positively
charged while the
opposite end is negatively
charged
slight negative charge at this end
O
H
H
slight positive charge at this end
slight negative charge at this end
O
H
but the whole
molecule has
no net charge
( + and - balance
each other)
H
slight positive charge at this end
H +
+
_
O
H +
H
+
+
_
O
H
+
Fig. 2.13, p. 28
Important Bonds in
Biological Molecules
• Hydrogen bonds
– Electronegative atom of a molecule weakly interacts
with a hydrogen atom
Hydrogen bonds may form
between two or more molecules
Elements of life
•
•
•
•
•
•
Carbon
Hydrogen
Nitrogen
Oxygen
Phosphorus
Sulfur
• CHNOPS