Chemistry of Life - Honors Biology - Honors Biology - 2011-08-20
Chapter 2: Chemistry of Life
Composition of Matter
Matter - anything that occupies space and has mass
Mass - quantity of matter an object has
weight - force produced by gravity acting on mass. You would weigh less on the moon because moon exerts less force on object than Earth does.
chemistry - study of how chemical changes in matter occur
Elements and Atoms
Elements - substances that can't be broken down chemically into simpler kinds of matter. More than 100 exist. Fewer than 30 important to living things. More than 90% of mass of living things is composed of 4 elements: Carbon, oxygen, hydrogen, and nitrogen.
Periodic table - lists information about the elements, including atomic number, chemical symbol, atomic mass.
atom - simplest particle of an element that retains all the properties of that element.
electron cloud model - most scientists see this as most accurate model of the structure of an atom. Proton, neutron, nucleus and electron cloud.
The Nucleus - central region of an atom. Makes up bulk of atom's mass. Consists of 2 subatomic particles: proton and neutron.
Proton - positively charged particle. Number of protons in an atom is designated by atomic number directly above chemical symbol.
Neutron - no charge.
Mass number - total number of protons + neutrons in an atom
Electrons - Negatively charged particles. Equal number of electrons and protons in an atom. Net electrical charge = 0. Electrons are high energy particles with very little mass. Move about nucleus at high speeds in orbital - 3-D region around nucleus. Electrons in orbitals farther away from nucleus have greater energy than those closer to nucleus. Combination of orbitals forms electron cloud. Orbitals correspond to specific eergy levels. First level can hold 2 electrons; 4 orbitals in 2nd energy level which can hold up to 8 electrons, with maximum of 2 electrons in each orbital.
Isotopes - atoms of same element that have different number of neutrons. Note: all atoms of an element must have same number of protons, but can have different number of neutrons. Most elements are made up of mixture of isotopes. Additional neutrons add mass.
Compounds - atoms of 2 or more elements combined in fixed proportions.
chemical formula - shows kinds and proportions of atoms of each element making up a compound. Ex. 2H + O=H2O=water.
How elements combine to form compunds depends on number and arrangement of electrons in their orbitals.
Chemical stability of atom - occurs when orbitals that correspond to its highest energy level are filled with maximum number of electrons.
Noble (inert) elements - consist of atoms that have max. number of electrons in orbitals of their hightest energy evels and do not react with other elements under normal conditions. Examples: Helium (He) and Neon (Ne).
Most atoms are NOT stable in their natural state. They tend to react with other atoms in different ways to become more stable. Carbon (C), Nitrogen (Ni), and Oxygen (O2) atoms have unfulfulled orbitals that correspond to their hightest energy levels. Most elements, like these, interact with other atoms to form chemical bonds.
Chemical bonds - attractive forces that hold atoms together.
Covalent Bonds - form when 2 atoms share one or more pairs of electrons. Ex: H2O. 2 H held together with 1 O by covalent bonds. They share electrons to become stable. Covalent bonding results in the formation of molecules.
molecule - simplest part of a substance that can exist in a free state. Ex. one molecule of compound water is H2O. One molecule of Oxygen is O2.
Ionic bonds - positive and negative electrical charges attract each other and form an ionic bond. Ex. Na+ and Cl- form NaCl (table salt).
A Na atom loses an electron to a Cl atom. Both atoms are now stable but carry a charge and become ions. Ions are attracted to each other and form an ionic bond: NaCl. By losing its outermost electron a sodium atom becomes Na+ ion. By gaining an electron, a chlorine atom becomes a Cl- ion. Due to their opposite charges, the Na+ and Cl- ions attract to one another and form an ionic bond: NaCl.
Section 2: Energy
All living things use energy. Amount of energy in universe remains constant over time, but can change from one form to another. Transfer of energy from sun and through almost every organism on Earth is important in chemistry of living things.
Energy and Matter
Energy - ability to do work. Can occur in various forms. Radiant-light; thermal-heat. chemical, electrical, mechanical
States of Matter: Solid, Liquid, Gas
solid - more closely linked together (exception=H2O); particles move less rapidly. Maintains fixed volume and shape.
liquid - maintains fixed volume but particles move more freely and shape can conform to shape of any container.
gas - partcles move most rapidly. Have little if any attraction to each other. Fill volume of container occupied.
Thermal energy is needed to cause a substance to change from one state to another.
Energy and Chemical Reactions
chemical reaction - one or more substances change to produce one or more differnt substances. Energy is absorbed ore released when chemical bonds are broken and new ones are formed. Living things undergo thousands of chemical reactions each day.
reactant - substance or molecule that participates in a chemical reaction.
If reaction proceeds in only one direction, reactants are shown on left side of chemical equation. Products of chemical reaction are shown on the right side of the equation. The number of each kind of atom must be the same on either side f the arrow. Some chemical reactions are bidirectional. A 2-way arrow is used to depict this. For example, CO2+H2O ? H2CO3.
metabolism - energy used by body for chemical reactions. Uses sugars, proteins, fats from foods.
Activation Energy - amount of energy needed to start a reaction.
catalyst - chemical substances that reduce the amount of activation energy required for a chemical reaction to take place. In living things, enzymes act as catalysts.
enzyme - protein or RNA molecule that speeds up metaolic reactions without being permanently changed or destroyed.
Oxydation-Reduction Reactions (Redox reactions)
There is a constant ransfer of energy into and throughout living things.
redox reactions - Reactions in which electons are transferred between atoms.
oxidation reaction - reactant loses one or more electrons, thus becoming more positive in charge. Na ? Na+
reduction reaction - reactant gains one or more electrons thus becoming more negative in charge. Cl? Cl-
redox reactions always occur together
Section 3: Water and Solutions
Polarity - uneven distribution of charge across a molecule or compound
solubility of water - polar nature of water allows it ot dissolve polar substances, like sugars, ionic compounds, and some proteins. Water does not dissolve nonpolar substances, such as oil because a weaker attraction exists between polar and non-polar molecules than between 2 polar molecules.
Hydrogen Bonding - polar nature of water causes water molecules to be attracted to one another. Attraction is called a hydrogen bond - the force of attraction between a hydrogen molecule with a partial positive charge and another atom or molecule with a partial or full negative charge.
Hydrogen bonds in water eert attractive force strog enough that water "clings" to itself ad some other substances.
Hydrogen bonds form, break, and reform with great frequency. Number that exist depends on state water is in. In solid state all its water molecules are hydrgen bonded and don't break. Hydrogen bonding accounts for unique properties of water, nameley cohesion and adhesion, the ability of water to absorb a relatively large amount of energy as heat, the ability of water to cool surfaces through evaporation, the density of ice, and the ability of water to dissolve many substances.
Cohesion and Adhesion
cohesion - attractive force that holds molecules of a single substance together. Responsible for water moving upward from plant roots to leaves.
surface tension of water - cohesive forces resulting from ydrogen bonds cause molecules at surface of water to be pulled downward into the liquid. Can be observed in bulge above rim of overfull glass of water or as small creatures like water-striders run on water w/o breaking the surface.
adhesion - attractive force between 2 particles of different substances, such as water molecules and gas molecules.
capillarity - attraction between molecules that results in rise of surface of liquid when in contact with solid.
Temperature Moderation - Water has high heat capacity related to hydrogen bonding. Can absorb or release large amounts of energy in form of heat with only slight change in temperature. On hot summer day, water can absorb large quantity of energy from sun and can cool the air w/o a large increase in water's temperature. At night, gradual cooling of the water warms the air. Earth's oceans stabilize global temperatures enough to allow life to exist.
Density of Ice - unlike most substances, the density of solid water (ice) is less than liquid wateuid water because of the structure of ice crystals. This is due to shape of molecule and hydrogen bonding. Ice is less dense than liquid water because of the structure of ice crystals. Water molecules in ice are bonded to each other in a way that creates large amounts of open space betwee the molecules, relative to liquid water.
solution - mixture in which one or more substances are uniformly distributed in another substance. Can be mixutures of solids, liquids, or gases. For example, plasma is composed of many types of ions and large molecules and gases dissolved in water.
solute - substance dissolved in a solvent. Particles may be ions atoms or molecules.
solvent - substance in which the solute is dissolved.
Example: sugar is solute. Water is solvent to create sugar water.
concentration - amount of solute dissolved in a fixed amount of solution. Can vary. For example,a 2 percent saltwater solution contains 2 g of salt dissolved in enough water to make 100 ml. of solution.
saturated solution - one in which no more solute can dissolve.
aqueous solutions - solutions in which water is the solvent - univesrally important to living things. Most chemical reactions that occur in the body occur in aqueous solutions.
Acids and Bases
ionization of water - H20 ? H+ + OH-
OH- ion is known as hydroxide ion. The free H+ io can react with anothe water molecule:
H+ + H2O?H3O+
H3O+ is known as the hydronium ion.
acidity/alkalinity - measure of relative amounts of hydronium ions and hydroxide ions dissolved in a solution.
acids - number of hydronium ions in solution >number of hydroxide ions; sour taste; can be highly corrosive
bases - number of hydroxide ions > number of hydronium ions in solution; tend to feel slippery
pH - scale from 0-14 to measure acidity/alkilinity. 0 is extremely acidic; 14 is extremely basic; 7 is neutral. Logarithmic scale. Change of one pH unit reflects 10-fold change in acidity or alkalinity. Can be measured with litmus paper.
buffers -chemical substances that neutralize effects of adding small amounts of either an acid or a base to a solution to neutralize its pH.