Life depends on chemistry –all living things are made from chemical compounds which are used in chemical reactions to keep organisms alive ELEMENT – made up of one kind of atom Cannot be broken down into other substances by chemical means More than 100 known, about 24 found in living organisms

CHEMICAL COMPOUND _- substance formed by the chemical combination of one or more elements in definite proportions Shown by a short hand form called CHEMICAL FORMULA which uses SYMBOLS Physical and chemical properties usually very different from those of the elements from which they are formed Silvery metalYellowish gas

ATOM – basic unit of matter made up of subatomic particles PROTONS - positively charged (+) NEUTRONS – no charge Strong forces bind protons and neutrons bind together – NUCLEUS – at the center ATOMIC NUMBER= # of Protons ELECTRON – negatively charged (-), are in constant motion

ISOTOPES – same number of protons in their atoms but different numbers of neutrons RADIOACTIVE ISOTOPE _ nucleus breaks down or decays overtime, giving off radiation in the form of matter and energy Bone scan using isotope

ELECTRONS AND REACTIVITY – Electrons in the highest energy level of an atom determines how the atom reacts 1 st / lowest energy level – can hold 2 electrons 2 nd / highest energy level – can hold 8 electrons, when there is a partially filled energy level the atoms become chemically reactive, tend to react with other atoms Partially filled energy levels

Ionic Bond – when an atom transfers an electron to another atom An atom that loses electrons has a positive charge An atom that gains electrons has a negative charge

Covalent Bonds – when two atoms share electrons When the atoms share 2 electrons the bond is called a single covalent bond Sometimes,atoms share 4 electrons and form a double bond

2 or more atoms held together by covalent bonds form a MOLECULE Can be modeled as a STRUCTURAL FORMULA – which is the number and types of atoms linked together by bonds Number and types of atoms in a molecule are designated by a CHEMICAL FORMULA SPACE FILLING MODEL – drawing that depicts a 3- dimensional model

Molecules become rearranged into other molecules as existing chemical bonds break (absorbing energy from the surroundings). Such changes, which result in the formation of one or more new substances are called CHEMICAL REACTIONS Starting materials for the reaction – REACTANTS Ending materials in the reaction - PRODUCTS Hydrogen +Oxygen  Water + Energy ReactantsProducts

Water molecule Water Molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms- so they have regions with partial positive and negative charge ADHESION – attraction between unlike molecules COHESION – tendency of molecules of the same kind to stick together. Much stronger for water than most liquids

LOW DENSITY OF ICE – high density substance is always “tightly packed” than a low density substance Water is the opposite – solid form(ICE) is less dense –so it floats Floating ice insulates the water below allowing life to persist

THERMAL ENERGY – total amount of energy associated with the random movement of atoms and molecules in a sample TEMPERATURE- measure of the average energy of random motion of the particles in a substance When 2 substances differ in temperature, thermal energy in the form of heat is transferred from the warmer to the cooler one

SOLUTION – a uniform mixture of 2 or more substances SOLVENT – the substance that dissolves the other substance (water), Present in a greater amount SOLUTE – the substance that is dissolved. Present in a lesser amount AQUEOUS SOLUTION _ when water is the solvent Water surround and separates the positive and negative ions

Some materials do not dissolve when placed in water but separate into pieces so small that they do not settle out. The movement of water molecules keep the small pieces suspended. Such mixtures of water and non dissolved materials are known as SUSPENSIONS EXAMPLE - blood

ACIDIC SOLUTIONS – contain higher concentrations of H+ ions than pure water and have pH values from 1-6 ALKALINE (BASIC) SOLUTIONS - lower concentrations of H+ than pure water and have pH values of 8-14, higher concentrations of OH- pH SCALE – how acidic or alkaline (basic) a solution is

BUFFERS are weak acids or bases that can react with strong acids or bases to prevent sharp changes in pH Important – because molecules in cells are very sensitive to concentrations of H+ or OH- ions. Even the slightest maybe harmful to living things. If acids and bases are in equal proportion and there is no excess of either H+ or OH- the solution is NEUTRAL and the process is called NEUTRALIZATION

If acids and bases are in equal proportion and there is no excess of either H+ or OH-, the solution is called NEUTRAL and the process is called NEUTRALIZATION