8/12/13
LEAP Bio 8th Grade
• Our bodies
• Bodies of other organisms
• Physical environment
• Life 1st evolved in water
• All living organisms require water
• Chemical reactions in your body occur in cells consisting of 70%
- 90% water
Elements, atoms, and Compounds
• Smallest unit of matter that still retains property of an element
• Substance that cannot be broken down into other substances
• Atoms of same element that differ in the number of neutrons
that they contain
• Different isotopes of an element have
• - same # of protons
• -different # of neutrons
• Behave identically in chem reactions
• Substance consisting of 2+ different elements in fixed ratio
• Organisms are composed of elements In combinations called
compounds
• Protons and neutrons have same mass
• Atomic number = number of protons
• Atomic mass number = sum of protons and neutrons in nucleus
• Substance consisting of two or more different elements in a
fixed ratio
• More common than pure elements
• Molecule that contains at least 2 different element
• All compounds are molecules
• In radioactive isotopes the nucleus decays spontaneously giving
off particles and energy
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Oxygen
Carbon
Hydrogen
Nitrogen
• Are essential
• Only needed in small quantities
• Of the three subatomic particles only electrons are directly
involved in chemical activity
• E occur in energy levels called electron shells
• Distribution of electrons determines the atom’s chemical
properties
• # of e in outer shell determines chem prop of atom
• Atoms whose outer shells are not filled tend to interact with other
atoms and participate in chemical reactions
• Atoms with incomplete outer shells react so both atoms end up
with completed outer shells
• These atoms may react with each other by;
• Sharing
• Donating
• Receiving e
• These interactions result in atoms staying close together, held by
attractions called chemical bonds
• Strongest chemical bond
• 2 atoms share one+ outer shell e
• 2 or more atoms held together by covalent bonds form a molecule
• Covalent bonds join atoms into molecules htrough e sharing
• Atoms in covalent bond compete for shared e
• Attraction for shared e is called electronegativity
• More electronegative atoms pull harder
• Unfair sharing of e
• Water molecules are polar
• Oxygen has higher electronegativity than Hydrogen
• In molecules of one element the pull toward each atom is =
• Because each atom has same electronegativity
• Ion – atom/molecule with charge
• 2 ions with opposite charges attract each other
• When attraction holds ions together it is called ionic bond
• Salt is synonym for an ionic compound
• The charged regions on molecules are electrically attracted to
oppositely charged regions neighboring molecules
• Because the positively charged region is always a hydrogen
atom the bond is called a hydrogen bond
• When molecules are close together a slight attraction can
develop between the oppositely charged regions of nearby
molecules
• Chemists call such intermolecular forces Van Der waals forces
after the guy who discovered them
• Not as strong as other bonds
• Especially good at holding large molecules together
• Photosynthesis is a chem reaction
• Co2 reacts with water
• Sunlight powers conversion to produce the products glucose and
oxygen
• Remember that the structure of atoms and molecules determines
how they behave
• Hydrogen bonds make liquid h2o cohesive
• Cohesion – tendency of molecules of the same kind to stick
together
• It is much stronger for water than other liquids
• Most plants depend on cohesion to help transport water and
nutrients from their roots to their leaves
• Adhesion - Tendency of 2 molecules to stick together
• Cohesion is related to surface tension – a measure of how
difficult it is to break surface of a liquid
• Hydrogen bonds give water high surface tension, making it
behave as if it were coated with an invisible film
• Water striders stand on water without breaking the water’s
surface
• Because of hydrogen bonding water has the ability to resist
temp change than other liquids
• Heat = energy associated with movement of atoms and
molecules in matter
• Temperature = measures intensity of heat
• Heat is released when hydrogen bonds form
• Heat must be absorbed to break hydrogen bonds
• When a substance evaporates the surface of the liquid that
remains behind cools down in the process of Evaporate Cooling
• This cooling occurs because the molecules with the greatest
energy leave the surface
• When water freezes each molecule forms stable hydrogen
bonds with its neighbors
• As ice crystals form the molecules are less densely packed than
in liquid water
• Water is less dense as a solid than a liquid because of
hydrogen bonds (Ice floats)
• Hydrogen bonds are stable in in ice
• A solution is a liquid consisting of a uniform mixture of 2+
substances
• Dissolving agent is solvent
• Substance that is dissolved is solute
• Aqueous solution is one in which water is the solvent
• Water’s versatility as solvent results from the polarity of its
molecules
• Polar/charged solutes dissolve when water molecules surround
them, forming aqueous solutions
• Table salt is an ex of a solute that will go into solution in water
• In aqueous solutions a small % of water molecules break apart
into ions
• Some are hydrogen ions (H+)
• Some are hydroxide ions (OH-)
• Both are very reactive
• Acid – compound that releases H+ to a solution
• Base- compound that accepts H+
• The ph scale determines how acidic or basic a solution is
• The ph scale 0-14
• 0 = most acidic
• 14 = most basic
• Each ph unit represents a tenfold change in concentration of H+
• A buffer is a substance that minimizes change in ph
• Accept H+ when it is in excess
• Donates H+ when it is depleted
• Sulfur and nitrous oxides react with water in air to form acids
• These acids fall to earth as Acid precipitation which is rain,
snow, or fog with a ph lower than 5.2
• CO2 dissolving in seawater lowers ocean ph in a process called
Ocean Acidification
Quiz #1
I think this was the stuff to know for the very first quiz
• Describe importance of chem elements to living organisms
• Explain formations of compounds
• Describe atom structure
• Distinguish btwn ionic, covalent, and hydrogen bonds
• Define chem reaction and explain how it changes composition of
matter
• Describe importance of chem elements to living organisms
• Explain formations of compounds
• Describe atom structure
• Distinguish btwn ionic, covalent, and hydrogen bonds
• Define chem reaction and explain how it changes composition of
matter
• List/define life supporting properties of water
• Explain ph scale