Chapter 2: Chemistry 2-1 Composition of Matter 2-2 Energy 2-3 Solutions

2-1 Composition of Matter I. Matter In an organism, matter REARRANGES through chemical reactions. (1) Mass (biomass) AMOUNT of matter an organism occupies ( “mass” vs. “weight.”)

II. Elements (i.e., pure substances that cannot be broken down) > 90% of biomass of ALL LIFE is a combination of 4 elements: Oxygen (O) Carbon (C) Hydrogen (H) Nitrogen (N)

III. Atoms Simplest PARTICLE of an element with PROPERTIES of that element. (A) Nucleus CORE of atom, consists of 2 kinds of particles… (a) Protons (P+) (b) Neutrons (No zero charge)

(1) Atomic Number Number of PROTONS (AND e -) in an atom.

(B) Electrons (e-) Small, (-) charged particles that OFFSET (+) charged protons, making net e- charge of atom = ZERO.

1st Level seeks to hold 2 e- (1) Energy Levels Orbitals contain swarming e- in specific NUMBERS. (NOTE: Outer energy levels can hold MORE e- than inner levels) 1st Level seeks to hold 2 e- 2nd Level seeks to hold 8 e- 3rd Level seeks to hold 18 e- 4th Level seeks to hold 32 e-

Critical Thinking (1) In the early 1900s, HYDROGEN gas was used to inflate airships. After one large airship crashed and caught on fire, HELIUM gas began to be used to inflate airships. Why might have been helium preferred over hydrogen?

IV. Compounds (organic vs. inorganic, e.g., water, salt) A STABLE molecule of TWO or more TYPES of atoms.

(1) Chemical reactions occur when… Atoms COMBINE through e- pairing to become STABLE COMPOUNDS.

(2) Bonds (due to e- ) FORCES between atoms due to electron proton interaction.

(A) Covalent Bonds Two atoms SHARE one or more pairs of e- between each other. (1) Molecules Result from CHEMICAL BONDING between e- of atoms.

Critical Thinking (2) Hydrogen gas EXISTS as H2, rather than H. Why is this so?

(B) Ionic Bonds One atom DONATES one or more e- to another atom. (1) Ions Atoms WITH an electrical charge, be it positive (Na+) or negative (Cl-)

2-2 Energy (A) Energy in Living Things (1) Free Energy (NRG) NRG in an organism that is AVAILABLE for work (i.e, growth, reactions, development).

(B) States of Matter (changes REQUIRES free NRG) (1) Solid Particles close together, fixed shape and volume.

(2) Liquid Particles LESS packed together, fixed volume and FLEXIBLE shape.

(3) Gas Particles FAR apart, move rapidly, NO fixed volume or shape. NOTE: To CHANGE from a solid to a liquid, and from a liquid to a gas… Thermal energy must be ADDED. To cause the REVERSAL … Thermal energy must be REMOVED.

II. Energy and Chemical Reactions Cells undergo RXNS as part of life, thus need NRG to survive.

CO2 + H2O  H2CO3 (1) Reactants are… On LEFT side of a rxn. (2) Products are… On RIGHT side of a rxn.

(A) Energy Transfer NRG is RELEASED from compounds (FOOD) for use by CELLS.

(1) Exergonic Reactions (MOST living RXNS) PRODUCE a net RELEASE of free NRG to be harvested. (2) Endergonic Reactions REQUIRE a net ABSORPTION of free NRG.

Critical Thinking (3) Living things need a CONSTANT supply of energy, EVENTHOUGH many of the chemical reactions they undergo RELEASE energy. WHY might this be true?

(B) Activation Energy For ALL rxns, NRG must be ADDED to reactants to KICK-START the reaction.

(1) Catalysts REDUCE the amount of act. NRG needed to RUN a reaction, thus SPEED RXN rate up (e.g., speeding up your metabolism).

(2) Enzymes PROTEIN catalysts tailored to run CHEMICAL REACTIONS.

(C) Reduction-Oxidation Reactions (Redox Reactions) Rxns that TRANSFER NRG in cells use TRANSFER of e-.

(1) Oxidation Reactions occur when… Reactant LOSES e-, thus becoming POSITIVE in charge. Ex: Na atom LOSES an e- to achieve STABILITY in an IONIC bond with Cl. Therefore, Na atom undergoes OXIDATION to become a Na + ion.

(2) Reduction Reactions occur when… Reactant GAINS e-, thus becoming more NEGATIVE in charge. Ex: Cl atom GAINS an e- to achieve STABILITY in an IONIC bond with Na. Therefore the Cl atom undergoes REDUCTION to become a Cl- ion. Note: Redox reactions ALWAYS occur TOGETHER.

Critical Thinking (4) A magnesium atom has TWO electrons in its outermost energy level. A sulfur atom has SIX electrons in ITS outermost level. HOW do you suppose the TWO atoms will react to form a CHEMICAL BOND? Explain WHY this is considered a REDOX reaction.

2-3 Solutions I. Describing Solutions MOST biomass is WATER chemical rxns occur in AQUAEOUS solutions. Ex: The PLASMA of your blood is a medium.

(1) The solute is… SUBSTANCE dissolved in solution (e.g., NUTRIENTS in blood). (2) The solvent is… Substance THAT does the dissolving (e.g., PLASMA of blood).

(3) The concentration is… MEASUREMENT of [SOLUTE] dissolved in SOLVENT. (4) A saturated solution is… NO MORE solute can be dissolved in SOLVENT. (5) An aqueous solution (aq.) is… Solution with WATER as SOLVENT.

II. Acids and Bases (A) Dissociation of Water Attraction between WATER molecules is so STRONG that OXYGEN of one water can REMOVE the HYDROGEN from another water.

The breaking APART of the water molecule into TWO ions of opposite charge is called “dissociation.” H2O  H+ + OH- OH- is known as the HYDROXIDE ION (BASE) The free H+ can react with another H2O as shown… H+ + H2O  H3O+ H3O+ is known as the HYDRONIUM ION (ACID)

(B) Acids (i.e., acidic solution) Number of H3O+ is GREATER than number of OH- Ex: Consider what happens when HCl, a gas, is dissolved in water. HCl  H+ + Cl-

(C) Bases (i.e., OR alkaline) Number of OH- is GREATER than number of H3O+ Ex: Consider what happens when NaOH, a solid, is dissolved in water. NaOH Na+ + OH-

(D) The pH Scale (pH = - log [H+]) is… Ranges 0-14 and measures [HYDRONIUM ions] (H3O+) and [HYDROXIDE ions] (OH-) in a solution.

Critical Thinking (5) The active ingredient in ASPIRIN is acetylsalicylic ACID. Why MIGHT doctors recommend BUFFERED (such as Bufferin) aspirin for some people who have a “sensitive” STOMACH?

(E) Buffers (exist in our body, work for ENZYMES!) Chemicals that NEUTRALIZE small amounts of EITHER acid OR base. (i.e, Brings pH CLOSER to NEUTRAL 7.0).

Extra Slides AND Answers for Critical Thinking Questions (1) Hydrogen is very reactive, while helium is relatively unreactive. (2) A hydrogen atom tends to covalently bond to another hydrogen atom, sharing electrons and becoming stable. (3) Even exergonic reactions need a small amount of activation energy to begin. (4) The magnesium atom will give up its two electron to the sulfur atom. As a result, both atoms will have eight electrons in their outermost energy levels and become stable. This a redox reaction because the magnesium atom has lost electrons, and the sulfur atom has gained electrons. (5) The buffer reduces the acidity of the aspirin and thus is less irritating to the stomach.