+ Good Afternoon Your tests are not completely graded but will be before the end of the day. We are going to go over the most often missed questions as well as the short answer parts. Today we start our new unit on BIOCHEMISTRY! Please answer this question in journal: How did you prepare/study for your test? If you did the USAtest prep practice tests do you feel they were helpful? (Be honest!) What will you change or do differently during the unit to help prepare for the next test to improve your average?

+ Chemistry Elements and Bonds

+ Why do we care about what atoms are made of??? Meet the Elements! Meet the Elements!

+ CHONPS- most important elements in biology 90 occur naturally 25 essential to living organisms C,H,O,N make up 96% of a human body

+ Chemistry of Life  All matter is composed of tiny particles called  atoms.  There are 109 types of atoms  A substance made-up of one kind of atom is called an element  An atom is the smallest part of an element that still has the properties of that element.

+ What makes up Atoms:

+ Periodic Table Atomic Number (number of protons & electrons) Atomic Mass (total of protons and neutrons) Isotopes – different number of neutrons Let’s Practice: C Atomic # _____ # p ____ #e _____ # n _____ N Atomic # _____ # p ____ #e _____ # n _____ O Atomic # _____ # p ____ #e _____ # n _____

ELECTRONS Electrons are found on multi- layered shells that swirl around the nucleus of an atom at the speed of light. The electrons on the outermost shell are called valence electrons Inner shell can hold 2 Next shell can hold 8 Outer shell can hold 8 When outermost shells are not filled with electrons, atom is unstable and reactive, more likely to form bonds.

+ Molecules and Compounds When two or more atoms bond, they form a molecule. A compound is a substance made of 2 or more different elements

+ STOP AND JOT How is it that two atoms can make a molecule but not a compound?

+ Covalent Bonds Formed when atoms “share electrons”

+ Why do elements bond? Elements bond(stick together) based on the number of their valence electrons (out ring of electrons) Rule of 8 If the outer ring of electrons is not full with 8 total electrons, the atom will bond to complete it’s outer ring. (Hydrogen’s outer ring is full with 2)

+ How to bond elements: Figure out how what group each element is in. If the element is neutral, the number of valence electrons are that number That number is how many available e- the element has available to bond Put that number of dots around each element Let’s Practice… O, H, H C, H, H, H, H Na, Cl

+ Ionic Bonds Formed when atoms lose or gain electrons (trade electrons) and become electrically positive or negative. The resulting opposite charges are drawn to each other.

+ Ionic Bondvs.Covalent Bond Atoms gain or lose electrons. Strong Bond Strength Breaks apart in water Atoms share electrons Medium Bond Strength Can single, double, or triple Bond Attraction between 2 or more atoms Caused by incomplete electron shells

+ Chemical Reactions Reactants Products Catalyst Metabolism © 2007, CSCOPE C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energy 6CO 2 + 6H 2 O + energy C 6 H 12 O 6 + 6O 2