Download The Chemical Basis of Life

THE CHEMICAL BASIS OF LIFE
CHAPTER 4
4.1 Life Requires…
• What are humans and other organisms made of?
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Matter
What is matter?
Anything that occupies space and has mass.
What are examples of matter?
Rock, wood, air, metal, animals.
WHAT ARE THESE?
• What is matter made of?
• Elements
• Element:
• A pure substance that can not be broken down
into other substances by chemical means.
• Are often described as the “basic ingredients”
of matter.
WHICH ELEMENTS ARE ESSENTIAL FOR
LIFE?
• Oxygen
• Carbon
• Hydrogen
• Nitrogen
• Make up 96% of the living matter in our body.
THE OTHER 4 % ARE
• Calcium, Phosphorus, Potassium, Sulfur, and few other
elements.
• These elements are called trace elements.
• Trace elements:
• Elements that make up less than .01% of your body mass, but
are still critical to have.
• Iron is a trace element (.004%)
• We need iron in our system to regulate our oxygen in our
blood.
• We get these elements in our diet.
WHAT DO YOU GET WHEN YOU MIX
SODIUM(NA) AND CHLORINE (CL)?
• Sodium chloride (NaCl)= salt!
• This is an example of a compound.
• Compound:
• Is a substance containing two or more elements that are
chemically combined in a fixed ratio.
4.2 CHEMICAL PROPERTIES
• The smallest possible particle is called an atom.
• Atom= atomos= invisible.
ATOM
• Atoms are made up of even smaller particles called subatomic
particles.
• What are the three subatomic particles?
• Protons
• Neutrons
• Electrons
WHAT KIND OF CHARGE DO THESE
HAVE?
• Protons:
• Positive electrical charge +
• Neutrons:
• No electrical charge 0
• Electrons:
• Negative electrical charge -
WHERE CAN THE PROTONS AND NEUTRONS BE
FOUND IN AN ATOM?
• Nucleus.
• Electrons (less mass than neutrons are found outside the
nucleus)
• All atoms of an element have the same number of protons.
This is called the atomic number.
• How many protons are in Carbon?
•6
• Atomic number= number of protons!
• Number of protons= Atomic number
• Number of electrons= Number of protons= Atomic
number
• Number of neutrons= Mass number – Atomic
number
HOW MANY ELECTRONS IS KRYPTON?
Mass number = (Number of protons) + (Number of neutrons)
84 = (Number of protons) + (Number of neutrons)
84 = 36 (number of neutrons)
48 number of neutrons
• Some elements have alternate forms called isotopes.
• Isotopes:
• An element that has the same number of protons but
different number of neutrons.
• Carbon 12 makes up of 99% of carbon.
• Carbon 13 and Carbon 14 are extremely rare.
• Carbon 14 is unstable and radioactive.
• Carbon 14 is a radioactive isotope.
• Radioactive isotope:
• The nucleus decays and gives off radiation.
How does an atom’s structure determine how it
reacts with other atoms?
• Electrons differ in the amount of energy they have and how
tightly they are held by the protons in the nucleus.
• An atom’s electrons belong to certain energy levels.
• Usually it is the electrons in the highest energy level that
determines how atoms react.
• The first or lowest energy level (closest to the nucleus) can
hold 2 electrons.
• The second energy level can hold 8 electrons.
• Helium has 2 electrons. Both of those electrons are found in
the lowest energy level.
• Since the lowest energy level is fully occupied it is less likely to
react.
WHAT WILL CARBONS ELECTRONS LOOK LIKE?
• Carbon has 6 electrons.
• Since 8 electrons can fit on the secondary energy level and is
not complete (stable) the outside 4 electrons are more likely
to react.
4.3 CHEMICAL BONDS
• What happens to the electrons when you mix sodium NA and
chlorine CL?
• The sodium that has one electron in its outer level
will move to the chlorine that has 7 electrons on the
outer level to make it stable.
• Now both are stable on the outside level.
• This is called an ionic bond.
• Ionic bond:
• Occurs when an atom transfers an electron to another atom.
• Now that chlorine gained an electron is has a – 1
charge.
• Sodium lost an electron so now its charge is +1.
• The two atoms are now referred to as ions.
• Ions:
• Atoms that have become electrically charged as a
result of gaining or losing electrons.
• Covalent bond:
• Forms when two atoms share electrons.
• Number of bonds: The number of bonds an atom can form is
equaled to the number of additional electrons that will fill its
highest energy level.
• How many bonds can hydrogen have?
• 1
• How many bonds can oxygen have?
• 2
• Two or more atoms held together by covalent bonds form a
molecule.
• Chemical formula: number and types of atoms in a molecule
• Structural formula: how atoms in a molecule are linked by
bonds.
• The formation of one or more new substances is called a
chemical reaction.
• Reactants: the starting materials for the reaction
• Products: the ending materials for the reaction
4.4 UNIQUE PROPERTIES OF WATER
• Water is a polar molecule. A polar molecule is
when the opposite ends have opposite electric
charges.
• The hydrogen in the water molecule is slightly
positive. The oxygen in water is slightly negative.
• Since opposites attract… two water molecules are
attracted to each other.
• Have you ever fell asleep before it rains and wake
up to go to the bus and see water covering
everything?
PROPERTIES OF WATER
• Adhesion: Water attracted to other substances.
• Cohesion: Water attracted to water.
• Objects can float because of waters surface
tension
• Surface tension: The bond between water
molecules.
• Does ice sink or float?
• Water is unique because its solid form is less dense
that its liquid form.
WATER CAN DISSOLVE OTHER
SUBSTANCES
• What happens when you mix salt in water?
• It dissolves.
• You just made a solution.
• Solution:
• A mixture of two or more substances.
• Solvent: the substance that dissolved the other substance and
is present in the greater amount.
• Solute: the substance that is dissolved and is present in a lesser
amount.
• If you take a pack of salt and mix in water… which is the solute
and solvent?
• Solute
• Salt
• Solvent
Water
ACIDS AND BASES
• Hydrogen ions (positive charge) makes things more
acidic.
• Acid:
• H+ ions added.
• Base:
• The removal of H+ ions.
PH SCALE
• pH scale:
• Describes how acidic or basic a solution is.
• Ranges from 0 (extremely acidic) to 14 (extremely
basic)
• 7 is neutral (pure water)
• Most living cells are near 7.
• Buffers:
• Substances that cause a solution to resist changes in pH.
• Human blood normally has a pH of 7.4
• When bloods pH decrease (drink lemon juice) and becomes
more acidic buffers come in and resist the blood to drop any
lower and acidic.