Transcript Chapter 2 - Chemical Context of Life

CHAPTER 2
The Chemical Context of Life
2.1 Matter is made of elements and
compounds.
Organisms are composed of matter anything that takes up space or has
mass

An element is a substance that cannot
be broken down by chemical reactions.


Fe, Ca, K
A compound is a substance consisting of
two or more elements in a fixed ratio.


NaCl, HCl, H2O2 , C6H12O6
Matter - elements and compounds

Life requires about 25 elements
 C,
O, H, and N make up 96% of all living
matter
 S, P, Ca, and K make up the remaining 4%

Trace elements are those that are
required, but only small amounts.

N and I
 Deficits
may have severe consequences
Nitrogen deficiency
- growth of plant
Iodine deficiency –
enlargement of thyroid
gland
Table 2.1
2.2 – An element’s properties depend
on its structure

An atom is the smallest unit of matter that
still retains the properties of an element.
 Similar

to a cell being the basic unit of life
Subatomic particles help us to better
understand atoms.
 Protons
(p+)
 Neutrons (n0 - no charge)
 Electrons (e-)
2.2 Properties and Structure

Atomic number is the # of p+
 In


neutral (uncharged atom) also equals e-
Mass number (Atomic mass) = p+ + n0
Isotopes are the different forms of an
element.
#
of n0 varies in the nucleus
 Often used as radioactive markers/tracers for
tests
You should be able to identify and determine
mass and atomic number for elements on the
p-table.
2.2 – Properties and Structure


The e- of an atom have different energy –
ability to do work.
e- have stored (potential)energy because
of their position in relation to the nucleus.
 1st
shell (closest to nucleus) least energy
 2nd shell more energy than 1st, etc.

Outer most shell contains valance e identified
by group number (groups ↑↓)
 # of unpaired e- indicates reactivity of
element
e- Energy Shells
Third shell (highest energy
level)
Energy
absorbed
Second shell (higher
energy level)
First shell (lowest energy
level)
Atomic
nucleus
Energy
lost
Valence e- of common elements
Hydrogen
1H
Atomic mass
First
shell
2
He
4.00
Atomic number
Helium
2He
Element symbol
Electrondistribution
diagram
Lithium
3Li
Beryllium
4Be
Boron
5B
Carbon
6C
Nitrogen
7N
Oxygen
8O
Fluorine
9F
Neon
10Ne
Silicon
14Si
Phosphorus
15P
Sulfur
16S
Chlorine
17Cl
Argon
18Ar
Second
shell
Sodium Magnesium Aluminum
12Mg
11Na
13Al
Third
shell
2.3 Chemical Bonding

Atoms will bond with other atoms to gain
stability.
 Stable
when valence shell is full.
 Covalent
bonds
 Ionic bonds
Chemical Bonding

Covalent bonds are formed when 2 atoms
share a pair or pairs of valence e-.
 Hydrogen
(H) atoms will share their e-. They
become H-H.
 H2O – H covalently bonded to O
 More
on this in Ch.3
2.3
2.3 – Chemical Bonding

Electronegativity is a measure of an atoms
ability to the attract the e- of another
atom to form a covalent bond.
 Sharing
of e- results in a strong bond.
 Two types of covalent bonds
 Nonpolar
 Polar
Covalent bonding…

Nonpolar when the e- are shared equally
 results

in no charge on either atom involved
Polar when one atom is bonded to a more
electronegative atom
 results
in charge (+/-) on one atom
Polarity of H2O
–
O
H
H
+
H2O
+
2.3 Chemical Bonding

Ionic bonds occur when two atoms are so
unequal in their attraction for e- that one
atom will strip the e- from its partner.
 These
bonds are not as strong as covalent
bonds.

An ion is a charged atom;
 Cations
have a “+” charge, ca+ion
 Anions have a “–” charge, a negative ion

Compounds formed by ionic bonds are salts.
Ionic Bonds
Na
Cl
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
Na+
Sodium ion
(a cation)
Cl–
Chloride ion
(an anion)
Sodium chloride (NaCl)
2.3 Chemical Bonding


The advantage of weak bonding is that the
contact/bond between atoms can be brief.
Hydrogen bonds occur when H is covalently
bonded to an electronegative atom and
attracted to another electronegative atom.
 Water
and ammonia
 Water and water
 Bases in DNA
Hydrogen Bonding

+
Water
(H2O)
+
Hydrogen
bond

Ammonia
(NH3)
+
+
+
Hydrogen bonding…
Hydrogen bonding…
Shape and Function

Molecules have distinct shape and size
 Related

to atoms and bonds contained within
As mentioned before shape/structure is directly
related to function
 Determines
how molecules interact and respond to each
other
 Opiates
and endorphins – chemicals with similar shapes
interact with similar receptors on the brain, causing similar
effects
2.4 – Reactions make or break
bonds.

Chemical reactions involve breaking and
making new chemical bonds.
 Start
with reactants.
 End with products.
 Coefficient
each
 What
and subscript tells you how much of
is the reverse reaction of
photosynthesis?
Chemical Reactions
2.4 – Reactions make or break
bonds.

Chemical equilibrium occurs when the
forward and reverse reactions occur at
the same rate.
 Concentrations
have stabilized
 Concentrations are NOT equal each other