Transcript Chemistry of Life

Chemistry of Life
What’s the Matter?
Atom: The most basic unit of matter
• Not all atoms are the same
Elements: a pure substance that consists of one
type of atom.
• Represented by a one or two letter symbol
• 90 naturally occurring, 22 synthetic
• Of the 90 naturally occuring, only 25 are needed
by life.
• CHON makes up 96% of these 25.
• The different elements are determined by
amount and arrangement of sub- atomic
particles.
Subatomic Particles
Nucleus: Center of
Atom (+ Charge)
• Protons (+ charge)
• Neutrons (0 charge)
Cloud: around the
nucleus
• Electrons (- charge)
The Electron Cloud
Electrons are moving around the nucleus at
distinct energy levels (shells, or orbitals)
Each energy level has a limited capacity of
electrons.
• 1st (closest to nucleus) = 2 electron max
• 2nd and higher = 8 electron max
In their most isolated state, atoms have equal
numbers of electrons and protons so that they
have no overall charge
Atomic Properties
Atomic Number: The number of protons in
the nucleus.
• Determines which element is which
• Also indicates how many electrons will be
found in the cloud for that element.
Mass Number (Atomic Mass): The overall
mass of the atom of that element
• Sum of the number of protons and the
number of neutrons.
Knowing the atomic
number and the
mass number, how
could you determine
the number of
neutrons in the
nucleus of an atom?
• Mass # - Atomic # =
number of neutrons
• Isotopes
The Octet Rule
Atoms interact with each other in order to fill
their outer most energy level with
electrons. (usually eight)
• Most atoms do not have full outer shells
• Does CHON?
• This causes atoms to react with other
atoms (by forming bonds) to form
compounds.
Chemical Bonds
The emergent properties of a
compound. The metal sodium combines
with the poisonous gas chlorine to form the
edible compound sodium chloride, or table
salt.
Compounds
A substance formed by the chemical
combination of two or more elements in
definite proportions.
• Formed due to the needs of atoms to have
outer shells that are full with electrons.
• Nearly all matter on this planet exists in
the form of compounds
• What are the exceptions? ( hint: look at
the periodic table)
Types of bonds
1)Ionic Bonds: A bond that forms when
electrons are transferred from one atom
to another.
• When atoms gain or lose electrons they
become charged atoms called ions.
• The opposing charges of ions cause the
bond to form.
• How does sodium (Na) and chlorine (Cl)
interact? (hint: draw bhor models)
Mostly abiotic
factors form and
break Ionic bonds
Ca & Cl (hint:
think of quantity of
atoms needed)
Types of Bonds
2) Covalent Bonds: A bond that forms between
atoms when electrons are shared.
• The electrons actually travel in the orbitals of
both atoms aka “shared”.
• Ex. H & O, C & H, N & H, O &O
• Can have single covalent bonds (2 e-), double
covalent bonds (4 e-) or Triple(6e-)
• Molecules: Compounds that are held together by
covalent bonds.
• Typically biotic factors form and break covalent
bonds.
Water as a Molecule
Water is a polar molecule
Polarity: When the
sharing of electrons
in a molecule is
uneven.
This results in the
molecule having a
slight negatively
charged side and a
slight positively
charged side
Hydrogen Bonds
Because of their differing charges on either
side, polar molecules (like water) can form
hydrogen bonds.
• Week bond between the hydrogen of one
polar molecule and the oxygen from
another polar molecule
• Venn Diagram
Hydrogen bonds
between water
molecules. The charged
regions of a polar water
molecule are attracted to
oppositely charged parts of
neighboring molecules.
Each molecule can
hydrogen–bond to multiple
partners, and these
associations are constantly
changing. At any instant in
liquid water at 37ºC
(human body temperature),
about 15% of the
molecules are bonded to
four partners in short–lived
clusters.
Ice: crystalline structure and floating barrier. In ice, each molecule
is hydrogen–bonded to four neighbors in a three–dimensional crystal.
Because the crystal is spacious, ice has fewer molecules than an equal
volume of liquid water. In other words, ice is less dense than liquid
water. Floating ice becomes a barrier that protects the liquid water
below from the colder air. The marine organism shown here is called a
euphausid shrimp; it was photographed beneath the Antarctic ice.
Cohesion and Adhesion
Cohesion: The attraction between molecules
of the same substance
• Due to hydrogen bonding
• Results in the high surface tension of
water
Adhesion: The attraction between molecules
of different substances.
• Meniscus in a graduated cylinder.
Walking on
water. The high
surface tension of
water, resulting from
the collective
strength of its
hydrogen bonds,
allows the water
strider to walk on the
surface of a pond.
Due to what property
of water?
• Why is it unlikely
that two neighboring
water molecules
would be arranged
like this?
Copy this chart down on a separate sheet of paper
Demonstration
Wax paper
Notebook
paper
Coin
Observation of
water drop(s)
Conclusion
Acids, Bases, and pH
Acids: any compound that forms H+ ions in
a solution.
Bases: any compound that forms OH- ions
in a solution.
The pH scale: A measurement system that
uses the concentrations of H+ ions and
OH- ions in a solution