Download The Chemistry of Life Chapter 2

The Chemistry of Life
Chapter 2
Why should we study
chemistry in
Life depends on chemistry!
• When you eat food or inhale oxygen,
your body uses these materials in
chemical reactions that keep you alive.
• Just as buildings are made from bricks,
steel, glass, and wood, living things are
made from chemical compounds.
• Wouldn’t you want an architect to
understand building materials? Same
idea applies to geneticists, ecologists,
zoologists, botanists, biologists, and
etc.
• The study of chemistry begins with the basic
unit of matter…the
History
• Greeks were first to try to explain chemical
reactions
• 400 BC: thought all matter composed of:
–
–
–
–
Fire
Earth
Water
Air
• Democritus first used word “atomos”, meaning
indivisible
• Atoms are composed of 3 main
particles: (subatomic particles)
– Protons (+)
– Neutrons
– Electrons (-)
Protons and Neutrons
• Strong forces bind protons and
neutrons together to form the
nucleus, which is at the center of
the atom.
• Both particles have about the
same mass.
Electron
• Electrons are negatively charged
with about 1/1840 the mass of a
proton.
• They are in constant motion in the
space surrounding the nucleus.
• Atoms have equal numbers of
electrons and protons.
• Because these subatomic particles
have equal but opposite charges,
atoms are neutral.
Elements
• Elements are the building blocks
of all matter.
• Elements cannot be decomposed
into simple matter.
Group Number:
6 7 8
1
2
3 4 5
The Elements
• 110 known elements
• 88 occur naturally
The 110 elements form a plethora of
compounds, just as 26 letters of the
alphabet make a seemingly endless
number of words.
Atomic Number
Counts the number
of
protons
in an atom
Atomic Number on the
Periodic Table
Atomic Number
Symbol
11
Na
All atoms of an element have
the same number of protons
11 protons
Sodium
11
Na
Atomic Mass
• Mass of an atom.
• Approximately equal to the number
of protons and neutrons
• Find number of neutrons by
subtracting the number of protons
from the mass.
• Review:
• An element's atomic number tells how
many protons are in its atoms.
• An element's or mass number tells how
many protons and neutrons are in its
atoms.
Learning Check 1
State the number of protons for atoms of
each of the following:
A. Nitrogen
1) 5 protons
2) 7 protons 3) 14 protons
B. Sulfur
1) 32 protons
2) 16 protons
3) 6 protons
C. Barium
1) 137 protons 2) 81 protons
3) 56 protons
Solution AT 1
State the number of protons for atoms of each
of the following:
A. Nitrogen
2) 7 protons
B. Sulfur
2) 16 protons
C. Barium
3) 56 protons
The Periodic Table
Isotopes
• Isotopes are atoms that have the
same atomic number but different
mass number.
• Most elements have two or more
isotopes.
• Same chemical properties because
the electron number does not
change.
Isotope symbols
Mass number
A
Z
Atomic number
X
Example
11
B
5
•How many protons does this have?
•How many neutrons does this have?
•Is the “5” necessary ?
More about isotopes:
• Some isotopes have unstable nuclei
which break down over time.
• They are called radioactive
isotopes
• Some radiation is harmful.
• Radiation can also be useful
Radioactive Dating
Cancer
Treatment
Tracers with X-rays
Kill bacteria
Compounds
• Two or more elements chemically
combined in specific proportions
• Examples:
– Water
– Salt
– Sugar
H2O
NaCl
C6H12O6
Chemical Formulas
are used to
represent
compounds
More About Atomic
Structure
• The center of the atom is called
the nucleus.
• Electrons live in something
called shells.
• Shells are areas that surround
the center of an atom.
• A shell is sometimes called an
orbital or energy level.
More About Electrons
• Every shell can hold only so many
electrons
• The further from the nucleus, the more
electrons a shell can hold
Valence Electrons
• The electrons on the outside edge of
the atom
• This is where the action is- where
bonding takes place
• Atoms have no more than 8 valence
electrons
The Octet Rule:
• Atoms will combine to form
compounds in order to reach eight
electrons in their outer energy level.
This is very stable!
• Atoms with less than 4 electrons tend
to lose electrons.
•Atoms with more than 4
electrons tend to gain
electrons.
Ions
• Atoms with extra electrons or
missing electrons
– Extra electrons give an ion a negative
charge
– Missing electrons give an ion a
positive charge
If they have to choose, atoms would
rather be stable than neutral.
How Does This Happen?
Some atoms have a few too
many electrons
Some atoms only need a few
electrons
What do you do if you are a sodium (Na)
atom?
Go look for an atom that
wants it!
Ionic Bonding
• Attraction that holds oppositely charged
ions together.
• Formed by the transferring of electrons
What If No One Will Give Up
An Electron?
• Atoms with less than 8 valence electrons
can move close to each other and share
their electrons
• The electrons spend their time around
both atoms.
• And they lived happily ever after!
Van der Waals Forces
• There are small attractive forces
between all atoms
• Help to hold molecules to each
other
• Ex: Gecko
Why do compounds form?
• Atoms are trying to get 8 valence electrons
How do compounds form?
• By ionic or covalent bonding
How can you tell if a compound is
ionic or covalent?
• By the types of elements in the compound
• Ionic compounds form between
metals and nonmetals
• Covalent compounds form
between 2 nonmetals
Note Question :
Indicate whether a bond between the following
would be 1) Ionic
2) covalent
____
A.
sodium and oxygen
____
B.
nitrogen and oxygen
____
C.
phosphorus and chlorine
____
D.
calcium and sulfur
____
E.
chlorine and bromine
Indicate whether a bond between the following
would be 1) Ionic
2) covalent
_1_
A.
sodium and oxygen
_2_
B.
nitrogen and oxygen
_2_
C.
phosphorus and chlorine
_1_
D.
calcium and sulfur
_2_
E.
chlorine and bromine
2-2 Water is a Polar
Molecule
• Electrons are shared unevenly between
the oxygen atom and the hydrogen
atoms
Negative end
Positive end
• This causes water to be attracted to other polar
or charged particles
– Water is attracted to ions
– Water is attracted to itself, forming hydrogen
bonds
Hydrogen Bonds In Water Are
Responsible For:
• Surface Tension
– Jesus Lizard
• Adhesion
– Attraction between molecules of
different substances
– Graduate cylinder
• Cohesion
– Attraction between molecules of
the same substance
– Drops of water on a penny
Acids, Bases, and pH
• Water molecules form ions
– H2O
– Water
H+
hydrogen ion
OH+ hydroxide ion
+
• Very few ions are formed in pure water, but
there are equal numbers of hydrogen and
hydroxide ions
• Water is neutral!
pH Scale
• Measures concentration of hydrogen
ions in a solution
• Ranges from 0 to 14
• 7 is neutral
• 0-7 have more hydrogen ions (H+)
and are acidic
• 7-14 have more hydroxide ions (OH-)
and are basic
pH of common substances
pH and Homeostasis
• Maintaining a pH between 6.5 and
7.5 is important in cells
• Dissolved compounds called buffers
control pH
– Proteins
– Phosphates
– Hydrogen carbonate
Chemical Reactions
• When 2 or more substances change
into other substances, a chemical
reaction occurs
• Bonds are either broken or formed
Chemical Equations
• Represent a reaction
• Give the types and amounts of
substances that react and form
• Reactants “yields”
Products
• 2H2 + O2
“yields”
2H2O
Evidence of a Chemical
Reaction
• Precipitate is formed
• Gas is evolved
• Change in heat or light energy
Organic
Compounds
Organic Compounds
• Make up most of living organism
• C atom is “backbone”
• C can easily bond with 4 other
elements
Carbohydrates
• Energy source
• Made of C, H, & O
– Ex: Glucose (a sugar)
– Polysaccharides: many
simple sugars linked
together like a chain
Lipids
• Store more energy than CHOs
because the chains are
longer
• Ex: Fats, oils, waxes
• Won’t dissolve in water
Proteins
• Provide structure
– Ex: Collagen- makes up your skin,
muscles & bones
• Aid chemical activities in your body
– Ex: Enzymes- work to speed up
rxns in your body
Nucleic Acids
• Store hereditary information
–Ex: DNA(deoxyribonucleic
acid)
RNA(ribonucleic acid)