CHEMISTRYCHEMISTRY

Composition of Matter

Matter - Everything in universe is composed of matter Matter is anything that

occupies space or has massMass – quantity of matter an object has

Weight – pull of gravity on an object

ElementsElements 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

AtomsAtoms The simplest 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 NucleusThe Nucleus Central core Consists of

positive charged protons and neutral neutrons

Positively charged Contains most of

the mass of the atom

The ProtonsThe Protons All atoms of a given element have

the same number of protons Number of protons called the

atomic number Number of protons balanced by an

equal number of negatively charged electrons

The NeutronsThe 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 ElectronsThe 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 LevelsEnergy 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 TablePeriodic 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

CompoundsCompounds 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 FormulasChemical 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 differ 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

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 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

Energy and MatterEnergy and Matter Energy

The ability to do work or cause change

Occurs in various forms Can be converted to another

form Forms important to biological

systems are chemical, thermal, electrical and mechanical energy

Free energy is the energy in a system that is available for work

States of MatterStates 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 placeFixed volume and shape

Liquids Molecules not as tightly linked as a solid

Maintain fixed volumeAble to flow and conform to shape of container

GasMolecules 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

Energy and Chemical Reactions Living things

undergo thousands of chemical reactions as part of the life process

Many are very complex involving multistep sequences called biochemical pathways

Chemical equations represent chemical reactions

Reactants are shown on the left side of the equation

Products are shown on the right side

The number of each kind of atom must be the same on either side of the arrow (equation must be balanced)

Bonds may be broken or made forming new compounds

Energy TransferEnergy Transfer Much of the energy

organisms need is provided by sugar (food)

Undergoes a series of chemical reactions in which energy is released (cell respiration)

The net release of free energy is called an exergonic (exothermic) reaction

Reactions that involve a net absorption of free energy are called endergonic (endothermic) reactions

Photosynthesis is an example

Most reactions in living organisms are endergonic; therefore living organisms require a constant source of energy

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!

Reduction-Oxidation Reactions

Many of the chemical reactions that help transfer energy in living organisms involve the transfer of electrons (reduction-oxidation = redox reactions)

Oxidation reaction – reactant loses electron(s) becoming more positive

Reduction reaction – reactant gains electron(s) becoming more negative

Solutions

SolutionsSolutions A solution is a

mixture in which 2 or more substances are uniformly distributed in another substance

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)

H2O H+ (hydrogen ion) + OH- (hydroxide ion)

H+ + H2O H3O (hydronium ion)

Acids and BasesAcids and Bases One of the most important aspects

of a living system is the degree of acidity or alkalinity

AcidsAcids Number of hydronium ions in

solutions is greater than the number of hydroxide ions

HCl H+ + Cl-

BasesBases Number of hydroxide ions in

solution is greater than the number of hydronium ions

NaOH Na+ + OH-

pH ScalepH Scale logarithmic

scale for comparing the relative 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

BuffersBuffers 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