chemistry. composition of matter matter - everything in universe is composed of matter matter is...
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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
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