Ch.2 Chemistry of Life

Nature of Matter Atoms are made up of three subatomic particles Protons – Positive charge Neutrons – Neutral charge Electrons – Negative charge Protons and Neutrons are found in the center of the atom called the Nucleus. Electrons are in constant motion in the space surrounding the nucleus. Atoms have an equal number of protons and electrons so all atoms have no net charge (neutral charge)

Elements A chemical element is a pure substance that consists entirely of one type of atom. There are more than 100 known elements, however only about 2 dozen are commonly found in organisms. Elements are represented by a one or two letter symbol Ex. Carbon=C, Sodium=Na Atomic number the number of protons in the element Atomic mass the number of protons plus neutrons rounded to whole number

Isotopes Atoms of the element that differ in the number of neutrons they contain are called isotopes. All the isotopes of an element have the same number of electrons so they have the same chemical properties. Some isotopes are radioactive meaning that their nuclei are unstable and break down at a constant rate over time. Radioactive isotopes have a number of important scientific uses Ex: determine the age of rocks and fossils, treat cancer, kill bacteria, and can be used as tracers to follow movements of substances within organisms.

Chemical Compounds A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. Chemical formula is a shorthand way of writing the chemical composition of compounds. Ex: H2O The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed. The atoms in compounds are held together by chemical bonds -2 main types Ionic bonds Covalent bonds Ionic bond Covalent bond

Chemical Bonding The interactions of atoms from individual elements form chemical compounds is called chemical bonding. Chemical bonding occurs when atoms share, gain or lose electrons. An atom will bond with another atom if the bonding gives both atoms complete outermost energy level. The maximum number of electrons on the outermost energy level is shown as : 1st level= 2; 2nd level= 8; 3rd level= 8 ; etc.

Ionic Bonding Ionic bonding occurs when electrons are transfer (gained or lost) between two atoms. Ionic bonding generally occur between metals and nonmetals. Elements that lose or gain an electron become Ions which now have an electrical charges. Na+ Cl-

Covalent Bonding Covalent bonding occurs when atoms shared electrons. Covalent bond generally occur between nonmetals, except when hydrogen bonds with another nonmetal in column #17 then it is an ionic bond. Example: HCl

Van der Waals Forces Some atoms have a stronger attraction for electrons than do other atoms. Even when atoms in a covalent bond share electrons the share is not always equal. The rapid movement of electrons can create regions on a molecule that have a tiny positive or negative charge. When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules and these are called van der Waals forces. Although these forces are not as strong as ionic bods or covalent bonds, they can hold molecules together, especially when the molecules are large

Water Water is the single most abundant compound in most living things. A water molecule is polar because there is an uneven distribution of electrons between the oxygen and hydrogen atoms Water therefore has some very unique properties: Cohesion – attraction between molecules of the same substance Ex: water to water Adhesion – attraction between molecules of different substances Ex: water to glass

Solutions and Suspensions Mixture – a material composed of two or more elements or compounds that are physically mixed together but not chemically combined. There are two types of mixtures: Solutions – when the components are evenly distributed throughout the solution. a. solute – the substance that is dissolved b. solvent – the substance in which the solute dissolves 2. Suspensions – a mixture of water and nondissolved material

Acids, Bases, and pH Acids – are any compounds that forms H+ ions in solution (pH less than 7) Bases – are any compounds that produce hydroxide ions OH- in solution (pH above 7) Buffers are weak acids or bases that can react with strong acids or bases to prevent sharp, sudden changes in pH pH scale – a system used to indicate the concentration of H+ ions in a solution

Carbon Compounds (Organic Chemistry) There are four groups of organic compounds found in living things Carbohydrates – used as main source of energy in organisms, and some use them for structural purposes Lipids – (fats) used to store energy, make up membranes and waterproof coverings Nucleic Acids – (DNA, RNA) store and transmit heredity, or genetic, information Proteins – form bones and muscles, cellular transport, help fight disease, and some control the rate of reactions and regulate cell processes.

Chemical Equations A Chemical equation is a shorthand method of showing a chemical reaction Symbols and formulas are used to represent reactants and products. Reactants are chemicals that enter into a reaction. Products are the substance that is produce from a reaction. An Arrow, which is read “yields” shows the direction of the reaction. Chemical reactions are reversible.

Endothermic & Exothermic Reactions Exothermic reaction C6H12O6 + 602  6CO2 + 6H2O + Energy (reactants) (yield) (product) Endothermic reaction Light Energy + 6CO2 + 6H2O  C6H12O6 + 6O2 (reactants) (yield) (product)

Balancing Chemical Equations Atoms can be neither created nor destroyed by ordinary chemical reactions. Atoms will only change positions or form other compounds during a chemical reaction. If you start a reaction with a certain number of atoms in the reactants you will end with the same amount of atoms in the products of a chemical reaction. This is called balancing chemical equations H2 + O  H2O 2 Hydrogen 2 Hydrogen 1 Oxygen 1 Oxygen

Balancing Equations (con’t) Fe2O3 + 3C  3CO + 2Fe The large numbers in front of chemical formulas in equations are called coefficients. Coefficients represent the number of molecules. The small numbers to the lower right of chemical symbols are called subscripts. Subscripts represent the number of atoms. Equations are balanced by changing coefficients never by changing subscripts. An equation is not properly balanced if the coefficients are not written in lowest whole number ratio.

Diatomic Molecules Hydrogen H2 Nitrogen N2 When these elements are Oxygen O2 found by themselves in a Fluorine F2 chemical equation, they Chlorine Cl2 must have subscript of 2. Iodine I2 Bromine Br2

Balance these equations 1. ___ Na + ___ Cl2  ___ NaCl 2. ___S8 + ___ O2  ___SO3 3. ___HgO  ___Hg + O2 4. ___Al + ___FeO  ___Fe + ___Al2O3

Key to Equations 1. 2Na + Cl2  2 NaCl 2. S8 + 12O2  8SO3 3. 2HgO  2Hg + O2 4. 2Al + 3FeO  3Fe + Al2O3

Enzymes Enzymes speed up chemical reactions that take place in cells, also called catalysts Enzymes provide a site where reactants can be brought together to react Such a site reduces the energy needed for the reaction The reactants of enzyme-catalyzed reaction are known as substrates Enzymes are very important, they play essential roles in regulation chemical pathways, making materials that cells need, releasing energy, and transferring information