Transcript CHEMISTRY * Chapter 2

CHEMISTRY
Composition of Matter
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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
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Pure substances that cannot be broken
down chemically into simpler kinds of
matter
More than 100 elements (92 naturally
occurring)
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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
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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 Nucleus
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Central core
Consists of positive
charged protons and
neutral neutrons
Positively charged
Contains most of the
mass of the atom
The Protons
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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 Neutrons
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The number varies slightly among atoms of
the same element
Different numbers of neutrons produce
isotopes of the same element
Atomic Mass
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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
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Negatively charged high energy particles
with little mass
Travel at very high speeds at various
distances (energy levels) from the nucleus
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Electrons in the same energy level are
approximately the same distance from
the nucleus
Valence shells = energy levels
Each level holds only a certain number
of electrons
Valence Electrons
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Valence electrons are found in outer shell
of an atom
Valence electrons are the only electrons
that take part in chemical reactions
Energy Levels
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Energy levels are also known as
electron shells or electron clouds.
Atoms have 7 electron shells.
The first shell can only hold 2
electrons
Shells 2-7 can hold 8 electrons
(octet rule)
Periodic Table
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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
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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
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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
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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
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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
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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
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Formed when two atoms share one or more
pairs of electrons
Ionic Bonds
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Some atoms become stable by losing or
gaining electrons
Atoms that lose electrons are called
positive ions
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Atoms that gain electrons are called
negative ions
Because positive and negative electrical
charges attract each other ionic bonds
form
Isotopes
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Atoms with a different than average
number of neutrons.
Many are radioactive
Many are used for “Dating” a substance
Chemical Reactions and
Enzymes
Energy and Matter
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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 Matter
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Atoms are in constant motion
The rate at which atoms or molecules in a
substance move determines its state
States of Matter
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Solid
Molecules are tightly linked.
 Little energy
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Liquid
 Molecules
are not as
tightly linked
 Medium amount of energy
States of Matter
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
Energy and Chemical Reactions
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Living things
undergo
thousands of
chemical
reactions as part
of the life
process
Energy and Chemical Reactions
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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
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A+B
C+D
Energy Transfer
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Much of the energy
organisms need is
provided by sugar
(food)
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Undergoes a series of
chemical reactions in
which energy is
released (cell
respiration)
The net release of
free energy is called
an exothermic
reaction
Energy Transfer
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Reactions that
involve a net
absorption of free
energy are called
endothermic
reactions
Photosynthesis is
an example
Mix Barium
hydroxide and
aluminum
salt, and the
products
dissolve in
water of
hydration.
This is VERY
COLD!
Energy Transfer
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Most chemical reactions require energy to
begin
The amount of energy needed to start the
reaction is called activation energy
Catalysts
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Certain chemical
substances
(catalysts) reduce
the amount of
activation energy
required
Biological
catalysts are
called enzymes
Catalysts
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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
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Enzymes work on
substances called
substrates
Substrates must fit into
a place on an enzyme
called the active site
Enzymes are reusable!
Enymes end in (ase)
Solutions
Solutions
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A solution is a
mixture in
which 2 or
more
substances are
uniformly
distributed in
another
substance
Solutions
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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
Acids and Bases
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One of the most important aspects of a
living system is the degree of acidity or
alkalinity
pH Scale
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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
Acids
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Compounds that donate a proton (H+) when
dissolved in a solution.
the lower the pH the stronger the acid
0-6 on the pH scale
 HCl  H+ + Cl-
Bases
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Compounds that accepts a proton (H+)
when dissolved in a solution.
the higher the pH the stronger the base
8-14 on the pH scale
 NaOH  Na+ + OH-
Acids and Bases
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pH 7.0 is neutral
Buffers
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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)
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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