Transcript CHEMISTRY
CHEMISTRY Elements • Pure substances that cannot be broken down chemically into simpler kinds of matter • More than 100 elements (92 naturally occurring) • 90% of the mass of an organism is composed of 4 elements (oxygen, carbon, hydrogen and nitrogen) • A compound is a pure substance made up of atoms of two or more elements – The proportion of atoms are always fixed • Chemical formula shows the kind and proportion of atoms of each element that occurs in a particular compound C6H12O6 + 6O2 6H2O +6CO2 + 36ATP subscripts Coefficient • Molecules are the simplest part of a compound that retains all of the properties of the substance and exists in a free state • Some molecules are large and complex Chemical Formulas • Subscript after a symbol tell the number of atoms of each element • H20 has 2 atoms of hydrogen & 1 atom of oxygen • Coefficients before a formula tell the number of molecules • 3O2 represents 3 molecules of oxygen or (3x2) or 6 atoms of oxygen • The tendency of elements to combine and form compounds depends on the number and arrangement of electrons in their outermost energy level • Atoms are most stable when their outer most energy level is full • Most atoms are not stable in their natural state (If they’re full, they won’t react) • Tend to react (combine) with other atoms in order to become more stable (undergo chemical reactions) 1. What are the 4 most common elements found in living things? a. b. c. d. Hydrogen, sulfur, phosporous, calcium Nitrogen, hydorgen, carbon, oxygen Oxygen, sulfur, hydrogen, calcium Carbon, hydrogen, phosphorous, nitrogen Bonding with the four main Elements • • • • H-needs 1 electron O-needs 2 electrons N- needs 3 electrons C- needs 4 electron C6H12O6 + 6O2 Reactants 6H2O +6CO2 + 36ATP Products Chemical equations represent chemical reactions. Covalent Bonds • Formed when two atoms share one or more pairs of electrons Ionic Bonds • Some atoms become stable by losing or gaining electrons • Atoms that lose electrons are called positive ions • Atoms that gain electrons are called negative ions • Because positive and negative electrical charges attract each other ionic bonds form 2. Why do atoms form bonds? a. To change from a gaseous state b. To become more stable c. To build larger molecules d. To gather more electrons Energy and Matter • Energy – The ability to do work or cause change – Can be converted to another form Energy and Chemical Reactions • Living things undergo thousands of chemical reactions as part of the life process (Metabolism) Energy Transfer • Much of the energy organisms need is provided by sugar (glucose) • Undergoes a series of chemical reactions in which energy is released (cell respiration) 3. How many bonds can carbon atoms form? A. B. C. D. 1 2 3 4 4. Where are reactants found in a chemical equation? a. b. c. d. On the left side On the right side Beneath the arrow Above the arrow • Most chemical reactions require energy to begin • The amount of energy needed to start the reaction is called activation energy • Certain chemical substances (catalysts) reduce the amount of activation energy required • Biological catalysts are called enzymes • Enzymes are an important class of catalysts in living organisms – Mostly protein – Thousands of different kinds – Each specific for a different chemical reaction Enzyme Structure • Enzymes work on substances called substrates • Substrates must fit into a place on an enzyme called the active site • Enzymes are reusable! 5. The place on the enzyme into which the substrate fits is the __________ site. a. b. c. d. Reaction Metabolizing Catalyzing Active Solutions Solutions • A solution is a mixture in which 2 or more substances are uniformly distributed in another substance 6. An enzyme is a(n) a. Protein b. Element c. Substrate d. atom • Solute is the substance dissolved in the solution – Particles may be ions, atoms, or molecules • Solvent is the substance in which the solute is dissolved • Water is the universal solvent • Solutions can be composed of varying proportions of a given solute in a given solvent --- vary in concentration (measurement of the amount of solute) • A saturated solution is one in which no more solute can be dissolved • Aqueous solution (water) are universally important to living things • Dissociation of water – Breaking apart of the water molecule into two ions of opposite charge (due to strong attraction of oxygen atom of one molecule for H atom of another water molecule) – OH- (hydroxide ion) – H+ (hydronium ion) Acids and Bases • One of the most important aspects of a living system is the degree of acidity or alkalinity Acids • Number of hydronium ions in solutions is greater than the number of hydroxide ions Bases • Number of hydroxide ions in solution is greater than the number of hydronium ions pH Scale • concentrations of hydronium ions and hydroxide ions in a solution • ranges from 0 to 14 Each pH is 10X stronger than next e.g. ph 1 is 10 times stronger than ph 2 • the lower the pH the stronger the acid • the higher the pH the stronger the base • pH 7.0 is neutral Buffers • Control of pH is very important • Most enzymes function only within a very narrow pH • Control is accomplished with buffers made by the body • Buffers keep a neutral pH (pH 7) • Buffers neutralize small amounts of either an acid or base added to a solution • Complex buffering systems maintain the pH values of your body’s many fluids at normal and safe levels 7. A liquid that has a pH of 3 is a(n) a. Acid b. Base c. Neutral d. Ion