AP Biology Chemistry Notes Name: ___________________ As we work through the notes make sure you’re filling in the blanks and highlighting key terms. Jot any extra notes along the side.

The Chemistry of Life 2009-2010

Why are we studying chemistry? Chemistry is the foundation of Biology

Matter Is defined as anything that _______________ ____________________________________. It makes up all the things you see around you and the gases you don’t Matter is made of elements (______________ _____________________________________) Compounds are a substance consisting of _______________ elements bonded together.

The World of Elements, but we’ll focus on these essential elements: Na Mg P S K Ca About 25 elements are essential for life Four elements make up 96% of living matter: • carbon (C) • hydrogen (H) • oxygen (O) • nitrogen (N) Six elements make up most of remaining 4%: • phosphorus (P) • calcium (Ca) • sulfur (S) • potassium (K) • magnesium (Mg) • sodium (Na)

Subatomic Particles: Protons: are located in the _______ and have a _____ charge and weigh 1 atomic mass unit (amu) Electrons: are located in the _______ and have a _____ charge Neutrons: are located in the _______ and have a _____ charge and weigh 1 amu

Isotopes Atomic Number: ___________________ Mass Number:_____________________ Isotopes of an element has the same atomic number (protons) but different masses because of extra neutrons

Isotopes in Biology Low levels of radiation such as radioactive iodine or glucose allow researchers to trace the location and activity of the atom in living tissues; therefore these isotopes are called tracers (________________________) High levels of radiation can cause __________ ________________; careful use of radiation in turn can sterilize products and kill cancer cells.

Electrons and Energy Electrons occupy an orbital at some level near or distant from the nucleus of the atom. An orbital is a volume off space where an electron is most likely to be found; an orbital contains no more than _________________. The more distant the orbital, the more _____________ it takes to stay in the orbital.

Electrons and Energy When atoms absorb energy during ____________________, electrons are boosted to higher energy levels. The innermost shell of an atom is complete with_____electrons; all other shells are complete with ______ electrons.

Elements & their valence shells Elements in the same column have the same # of valence electrons & similar chemical properties Remember some food chains are built on reducing O to H2O & some on reducing S to H2S ELECTRONEGATIVITY Oxygen has medium electronegativity so doesn’t pull electrons all the way off hydrogen whereas chlorine would. So oxygen forms a polar covalent bond. Carbon has only a weak electronegativity so forms a nonpolar covalent bond

Chemical reactivity Atoms tend to _______________________________________ or This tendency drives chemical reactions… and creates bonds Ionic or Covalent bonds – –

Bonds in Biology Hydrogen bond Covalent bond – H2O H2O H2 (hydrogen gas)

Nonpolar covalent bond _____________________________________ Strong stable bond example: hydrocarbons = CxHx methane (CH4 ) Lots of energy stored… & released Pair of electrons shared equally by 2 atoms strong stable bond example: hydrocarbons = CxHx methane (CH4 ) balanced, stable, good building block

Polar covalent bonds ________________________________________________ Strong but ________________ Ex:_______________________ oxygen has stronger “attraction” for the electrons than hydrogen oxygen has higher electronegativity water is a polar molecule + vs – poles leads to many interesting properties of water… H Oxygen + – – Pair of electrons shared unequally by 2 atoms strong but interactive bond example: bonds within water = H2O oxygen has stronger “attraction” for the electrons than hydrogen oxygen has higher electronegativity water is a polar molecule + vs – poles leads to many interesting properties of water… – – +

Hydrogen bonding Polar water creates molecular attractions ____________________________________________________________________________________________________ also can occur wherever an -OH exists in a larger molecule Weak bond but common in biology They help maintain complex molecule’s structure H bonds H O APBio/TOPICS/Biochemistry/MoviesAP/03_02WaterStructure_A.swf attraction between H+ in one molecule to O- in another molecule weak bond example: bonds between water molecules leads to many interesting properties of water

Ionic Bonds . Forms ________________ _______________________ These bonds fill the outer shell making them more stable ions The attraction of oppositely charged ions holds the 2 atoms together.