Chapter 2 Week 1 & 2 of Trimester 1 8/12/13 LEAP Bio 8th Grade

Chemicals are the stuff that make up Our bodies Bodies of other organisms Physical environment

Life’s Chem is tied to water 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

atoms Smallest unit of matter that still retains property of an element

Element Substance that cannot be broken down into other substances

Isotopes 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

Compound Substance consisting of 2+ different elements in fixed ratio Organisms are composed of elements In combinations called compounds

Subatomic Particle Info Protons and neutrons have same mass Atomic number = number of protons Atomic mass number = sum of protons and neutrons in nucleus

Compound 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

Elements that make up 96% of weight of living organisms Oxygen Carbon Hydrogen Nitrogen

Trace elements Are essential Only needed in small quantities

Chemical Bonds

notes 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

Distribution of e determines an atom’s chemical properties 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

Covalent 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

Polar Covalent Bond Unfair sharing of e Water molecules are polar Oxygen has higher electronegativity than Hydrogen

Nonpolar Covalent bonds In molecules of one element the pull toward each atom is = Because each atom has same electronegativity

Ionic bonds 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

Hydrogen Bonds 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

Van Der Waals forces 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

Chem reactions make and break chem bonds 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

Water’s Life-Supporting Properties 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

Water’s life supporting properties 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

Water’s hydrogen Bonds moderate temp 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

Water is the solvent of life 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 is the solvent of life 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

The chem of life is sensitive to acidic and basic conditions 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 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

Acid precipitation 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

Ocean Acidification CO2 dissolving in seawater lowers ocean ph in a process called Ocean Acidification

Need to know for quiz # 1 Quiz #1 I think this was the stuff to know for the very first quiz Need to know for quiz # 1

Need to know for 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

Need to know 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