Chapter 2 Chemistry of Life Sec 1 – Composition of Matter Sec 2 – Energy Sec 3 – Water and Solutions

Matter Biologists need an understanding of chemistry. Living things are “wet bags of chemicals”. Matter: Something that takes up space and has mass. Mass: The amount of “stuff” or matter. Mass DOESN’T equal Weight Weight is the effect of gravity on mass Life is just one long series of chemical reactions.

Elements and Atoms Elements Can’t be broken down further More than 100 but only about 30 are biologically important. Organisms are mostly Carbon, Oxygen, Hydrogen and Nitrogen. Arranged in the Periodic Table by properties. The smallest amount of an element is an atom.

The Nucleus Made of Protons and Neutrons. Most of the atoms mass is in the nucleus. Atomic Number = Number of Protons Atomic Mass = Protons + Neutrons Protons are positively charged, neutrons are neutral. See figure 2-1 A = B + C We can rearrange this equation.

Electrons In a neutral atom, there are equal numbers of electrons and protons. Electrons have a negative charge. Found in a 3d region or “orbital” around the nucleus. Outer electrons have more energy and move faster. All together electrons form a cloud. Orbitals can only hold two electrons. Energy levels are made of one or more orbitals.

Isotopes Same number of protons but different number of neutrons. All atoms of an element have the same number of protons. Isotopes will have the same atomic number BUT a different mass number.

Compounds Atoms (elements) don’t usually exist alone. They are bonded to the same or different element. Compounds result when two or more atoms in fixed proportions. H2O NH3 CO2 Properties change when atoms combine. ex-NaCl Atoms react to get a “full” outer energy level of electrons. Not all elements react, inert or noble. Most atoms not stable, react and form chemical bonds.

Bonds Forms when two atoms share one or more electron pairs. Board drawing H2O CO2 Molecules are the simplest part of a substance that retains the properties. Glass of water  water molecule Breath of air  oxygen and nitrogen molecules. Ions are atoms with an electric charge. Board drawing NaCl Ions have charges that attract other ions making ionic bonds.

Section 2 - Energy Energy is the ability to do work or cause change. MANY FORMS- heat, light, sound, chemical… Can be converted from one form to another. Eat a meal and go work out. chemical  heat /mechanical energy Turn on a light electric  heat / light energy

States of Matter Atoms are always in motion! Even if we can’t see it. The motion leads to arrangements and spacing. Solid – def volume and shape – close atoms, fixed Liquid – def volume, variable shape – close atoms Gas – variable shape and volume – spaced out atoms Energy can cause a phase change from one state to another.

Energy and Chemical Reactions Reactions involve one or more substances changing to produce a different substance. Energy is absorbed or released when bonds break or form. TNT exploding releases energy, glucose formation absorbs energy C6H12O6 + 6O2  6CO2 + 6H2O CO2 + H2O  H2CO3 Reactants Products

Cont… Activation energy is usually needed to get a reaction started. Think about how a match starts a fire. Energy causes movement and change. Catalysts speed up / allow reactions to occur with less energy. Not used up in the reaction. Enzymes are biological catalysts.

Cont… Chemical reactions involve the transfer of energy via electrons. Called reduction oxidation or “redox reactions”. Electrons are lost in a oxidation. Electrons are gained in a reduction. NaCl – Na is oxidized, Cl is reduced.

Sec 2 – Polarity Unequal sharing of electrons results in polar molecules like H2O. Has a “net” positive and negative side that interact with other polar molecules. Allows water to dissolve may substances. Solvent/Solute Water/Sugar Hydrogen bonds form between positive hydrogen atoms and negatively charged atoms. -this gives water many of it’s properties.

Cohesion & Adhesion Cohesion is when one substance sticks to itself. -water sticking to water. ex. Surface Tension Adhesion is when two substances stick together. - tape sticking to wall. Water is excellent at moderating temperature. Solid water floats on liquid water… strange.

Solvent + Solute = Solution Solutions are uniformly distributed, same throughout. -can be mixtures of solids, liquid or gasses. Ex. Soda Solvent- what does the dissolving. Solute- what is dissolved. Concentration is amount of solute per solvent. Ex. g/ml Aqueous solutions have water as the solvent.

Acids & Bases Acidity and Alkalinity are key aspects of living systems. -acids bases Water ionizes meaning one molecule is torn in part resulting in an OH- and H3O+ hydroxide hydronium ions Acidity and alkalinity are measure of the ration of these ions.

Acids Have a higher ratio of hydronium H3O+ ions. HCl + H2O -step one: HCl  H+ +Cl- -step two: the H+ join the H2O forming many H3O+ Thus, HCl and water form an acid. Sour, destroy most metals, pH below 7

Bases Have a higher ratio of hydroxide OH- ions. NaOH + H2O -step one: NaOH  Na+ + OH- Thus, NaOH and water form an base. Bitter, slippery, pH above 7

pH Scale Ranges from 0 (strong acid) to 14 (strong base) Each step is a 10x difference in concentration. pH 3  pH 2 = 10 fold increase pH 3  pH 1 = 100 fold increase pH 3  pH 0 = 1000 fold increase pH of 1 indicates lots of H3O+ pH of 7 indicates balance of H3O+ and OH- pH of 13 indicates lots of OH-