CHEMISTRY

Composition of Matter Matter - Everything in universe is composed of matter Matter is anything that occupies space or has mass Mass – quantity of matter an object has Weight – pull of gravity on an object

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) Each element unique chemical symbol Consists of 1-2 letters First letter is always capitalized

Atoms The smallest particle of an element that retains all the properties of that element. Properties of atoms determine the structure and properties of the matter they compose Our understanding of the structure of atoms based on scientific models, not observation

The Nucleus 2 main regions: Central core & electron shell Consists of positive charged protons and neutral neutrons Nucleus is positively charged Contains most of the mass of the atom

The Protons All atoms of a given element have the same number of protons Number of protons called/determines the atomic number Number of protons balanced by an equal number of negatively charged electrons

The Neutrons The number varies slightly among atoms of the same element Different number of neutrons produces isotopes of the same element

Atomic Mass Protons & neutrons are found in the nucleus of an atom Protons and neutrons each have a mass of 1 amu (atomic mass unit) The atomic mass of an atom is found by adding the number of protons & neutrons in an atom

The Electrons Negatively charged high energy particles with little or no mass Travel at very high speeds at various distances (energy levels) from the nucleus

Electrons in the same energy level are approximately the same distance from the nucleus Outer energy levels have more energy than inner levels Each level holds only a certain number of electrons

Energy Levels Atoms have 7 energy levels The levels are K (closest to the nucleus), L, M, N, O, P, Q (furthest from the nucleus) The K level can only hold 2 electrons Levels L – Q can hold 8 electrons (octet rule)

Periodic Table Elements are arranged by their atomic number on the Periodic Table The horizontal rows are called Periods & tell the number of energy levels Vertical groups are called Families & tell the outermost number of electrons

Compounds Most elements do not exist by themselves Readily combine with other elements in a predictable fashion

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

Molecules are the simplest part of a substance 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 physical and chemical properties of a compound are different from the physical and chemical properties of the individual elements that compose it.

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 filled & won’t react with other atoms.

Most atoms are not stable in their natural state Tend to react (combine) with other atoms in order to become more stable (undergo chemical reactions) In chemical reactions bonds are broken; atoms rearranged and new chemical bonds are formed that store energy.

Covalent Bonds Formed when two atoms share one or more pairs of electrons

Ionic Bonds Some atoms become stable by losing or gaining electrons. These atoms are called Ions. 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

States of Matter Atoms are in constant motion The rate at which atoms or molecules in a substance move determines its state.

Solid Molecules tightly linked together in a definite shape Vibrate in place Fixed volume and shape

Liquids Molecules not as tightly linked as a solid Maintain fixed volume Able to flow and conform to shape of container

Gas Molecules have little or no attraction to each other Fill the volume of the occupied container Move most rapidly To cause a substance to change state, thermal energy (heat) must be added to or removed from a substance

Solutions

Solutions A solution is a mixture in which 2 or more substances are uniformly distributed in another substance

Water is the universal solvent 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 as solvent) 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) H2O  H+ (hydrogen ion) + OH- (hydroxide ion)

Acids and Bases One of the most important aspects of a living system is the degree of acidity or alkalinity

Acids Number of hydrogen ions in solutions is greater than the number of hydroxide ions HCl  H+ + Cl-

Bases Number of hydroxide ions in solution is greater than the number of hydronium ions NaOH  Na+ + OH-

pH Scale logarithmic scale for comparing the relative concentrations of hydrogen 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