Transcript Chemistry for Biology

The
Chemistry of Life
2007-2008
 Everything is made of matter
 Matter is made of atoms
Hydrogen
1 proton
1 electron
Oxygen
8 protons
8 neutrons
8 electrons
Proton
+
Neutron
0
Electron –
The World of Elements
H
C N O
Na Mg
P S
K Ca
Different kinds of atoms = elements
atoms
Atomic # = number of
protons
Atomic Mass = protons
+ neutrons
How do you figure out
how many neutrons in
an atom?
Electrons?
Practice
Symbol
Atomic
number
Mass
number
N
7
14
B
5
11
H
1
1
C
6
12
C
6
14
Protons
Neutrons
electrons
Isotopes!
 Same element
 Different number of
neutrons
 Mass number

relates to the
particular isotope
C14 and C12
Medical uses for radioactive isotopes
A PET scan is one of the
many medical uses for
radioactive isotopes
PET, short for positronemission tomography, can
detect intense chemical activity
in the body. Brightly colored
areas indicate elevated levels of
radioactively-labeled glucose
and high metabolic activity,
which is a strong indicator of
cancerous tissue.
Bonding properties
What’s the
magic number?
 Effect of electrons

chemical behavior of an atom depends on
number of electrons in its valence shell
How does this atom behave?
How does this atom behave?
Chemical reactivity
 Atoms tend to
complete a partially filled valence shell
or
 empty a partially filled valence shell

This tendency drives chemical reactions…
and creates bonds
–
–
–
Hydrogen bond
Bonds in Biology
 Covalent Bonds: atoms
H2O
share electrons (strong)
 Ionic bonds: give/take
H2O
electrons and oposites
attract
Covalent bond
 Van der Waals forces

Hydrogen Bonds!!
–
–
H2 (hydrogen gas)
Chemical Formula
A chemical formula shows the kinds and number of
atoms in a substance.
Letters are
used to
represent the
elements
Number of
molecules
Subscript is used to
represent the # of each
element (for example 2
Hydrogens) ones are
assumed
Covalent bonds
 Why are covalent bonds strong bonds?
two atoms share a pair of electrons
 both atoms holding onto the electrons
 very stable

 Forms molecules
H
–
H—H
–
H
O
Oxygen
H
H
H2 (hydrogen gas)
H2O (water)
Multiple covalent bonds
 2 atoms can share >1 pair of electrons

double bonds
 2 pairs of electrons

triple bonds
 3 pairs of electrons
 Very strong bonds
–
H
H–C–H
–
More is
better!
H
Nonpolar covalent bond
 Pair of electrons shared equally by 2 atoms

example: hydrocarbons = CxHx
 methane (CH4 )
balanced, stable,
good building block
Polar covalent bonds
 Pair of electrons shared
unequally by 2 atoms

example: water = H2O
 oxygen has stronger
+
“attraction” for the
electrons than hydrogen
 oxygen has higher
electronegativity
 water is a polar molecule
 + vs – poles
 leads to many interesting
–
Oxygen
H
properties of water…
+
–
H
–
–
Ionic Bonds
Electrons are
transferred
from one atom
to the other
making them
charged ions.
Opposites attract
All compounds have properties
that are different from the
elements that make them.
These are called Emergent
Properties
Emergent properties
+
CHEMICAL REACTIONS:
Describe the process in which elements react to
form new compounds.
 Result in the release or absorption of energy.
Ex. What does this chemical equation represent?
energy + 6CO2 + 6H2O
 C6H12O6 + 6O2
Sunlight + 6 carbon dioxide + 6 water molecules
reacts to form glucose + 6 oxygen gas molecules
He’s gonna
earn a
Darwin Award!
Any
Questions?
Do one brave thing today…then run like hell!