MATTER AND ATOMIC
STRUCTURE
matter = anything that takes up space and has
mass; amount determines mass of object
elements = cannot be broken down into simpler
form by ordinary chemical means
1. forms of matter that contain only one type of
atom
2. symbol of one or two letters represent each
3. periodic table = system for classifying
elements
4. most abundant elements in universe =
hydrogen & helium
5. silicon & oxygen make up 75% of earth’s
crust; 92 natural elements
atoms = smallest unit of an element that has
all the properties of that element
1. cannot be broken down into smaller
particles by ordinary processes
2. determines structure; arrangement and
types give matter its properties
ATOMIC STRUCTURE
1. nucleus = core (center)
a. protons = positive charge (p+)
b. neutrons = neutral; no charge (n)
c. has an overall positive charge due to
protons
2. electron cloud = area around the nucleus
a. electrons = negative charge (e-)
b. electrons can be anywhere within the
cloud
c. not considered in the mass of an atom
d. closer to nucleus → lower energy; far
away from nucleus → higher energy
atomic number = number of protons in
nucleus
1. also equals the number of electrons
2. unique to each element
3. when number of p+ equals the number of
e- → atom is neutral
4. if number of p+ change → new element
mass number = number of p+ and n in nucleus
1. measured with special unit called atomic
mass unit (u)
2. * increase in mass as number of p+ and n
increase
3. can use mass number and atomic number
to determine the number of protons,
neutrons, and electrons in an element
Ex: carbon(C) = 6p+ + 6n = 12
Electron Energy Levels:
1. energy levels = arrangement of electrons around an
atom
a. each has a specific amount of energy
b. each can only hold a certain number of electrons
1st level = 2e3rd level = 18 e2nd level = 8e4th level = 32 e2. electrons occupy one level at a time but can move to
higher or lower levels
3. outermost level can never hold more than 8ea. atoms with outer level
filled are most stable
b. will not lose or gain eeasily so do not form
compounds easily
4. valence electrons = outermost electrons; determine
chemical behavior of element
5. atoms without outer level filled tend to exchange
electrons
a. metals = have only one, two, or three e- in outer
level
1) good conductors of heat and electricity
2) malleable = can be hammered into thin sheets
3) ductile = can be drawn into wires
4) tend to give up electrons
b. nonmetals = have four, five, or six electrons in outer
level
1) tend to gain electrons when combine
isotopes = atoms of same element that have different
numbers of neutrons but have same numbers of
protons
1. does not change the actual element
2. atomic mass = average of mass numbers of all
isotopes of an element
3. radioactivity = spontaneous process in which an
unstable nuclei emits radiation
a. can cause change in number of neutrons and
protons
b. decay changes identity of an element
4. provides a way to determine
ages of ancient objects
Ex: carbon: carbon-12 = 6p+ & 6n;
carbon-14 = 6p+ & 8n
Combinations of Atoms
1. compound = substance that contains two or more
elements chemically combined
a. new substance with properties different from
properties of each element in it
b. when chemical change occurs → new substance is
formed
Ex: carbon dioxide = CO2
2. molecule = smallest complete unit of a compound
a. consists of at least two atoms, held together by
covalent bonds
b. diatomic molecules = made up of two atoms,
usually same element bonded together
Ex: O2, H2
c. each element has definite proportion to other
element
Ex: water = H2O carbon monoxide = CO
CHEMICAL BONDS
1. chemical bonds = forces that hold together atoms
when they combine
a. produce by interaction of electrons in outer levels of
two or more atoms
b. can form by sharing or transferring electrons
2. types of bonds
a. ionic bonds = form when electrons are transferred
from one atom to another
1) form by transfer of electrons from a metal to a
nonmetal
2) ions = atom or group of atoms that carry an
electrical charge
a) lose e- → positive charge; gain e- → negative
charge
b) those with opposite charges are attracted to each
other
Ex: Al3+, Cl-
b. covalent bonds = form when electrons are shared
between two or more atoms
1) each covalent compound consists of only one kind
of molecule
2) held together by weak forces of attraction; melts at
much lower temperature
3) polar molecule = have covalent bonds between but
atoms do not share electrons equally
c. metallic bonds = valence electrons are shared by all
atoms
1) positive ions of metal are held together by negative
electrons between them
2) allows metals to conduct electricity since electrons
can move freely throughout metal
chemical formula = symbols that represent a
compound
1. indicates what elements are present
2. indicates how many atoms of each element are
present
3. symbol itself indicates one atom is present
4. subscript = number used after the symbol to tell how
many atoms of an element are present if there are
two or more
Ex: H2O
H (hydrogen) = 2 O (oxygen) = 1
chemical reactions = change of one or more
substances into other substances
1. described by chemical equations
2. must balance chemical equation by
showing equal number of atoms for each
element on each side of equation
MIXTURES:
1. mixture = contains two or more substances not
chemically combined
a. each substance retains its own properties
b. components can be separated by physical means
2. heterogeneous mixture = components are easily
recognizable
Ex: soil
3. solution (homogeneous mixture) = one substance is
uniformly dispersed in another substance
a. one or more substances can/are dissolved in another
substance
b. parts:
1) solute = substance being dissolved (added)
2) solvent = substance the solute is dissolved in
(put into)
c. alloy = solution of two or more metals
Ex: brass, bronze
d. can be liquid, gas, or solid mixtures
Acids & Bases:
1. acid = solution that has a substance that produces
hydrogen ions (H+)
a. most common acid in environment = carbonic acid
b. major role in dissolution of minerals in soil
2. base = solution that has a substance that produces
hydroxide ions (OH-)
3. pH scale = measure hydrogen and hydroxide ions in
solutions
a. pH = 7 (neutral)
b. pH > 7 (basic)
Base
c. pH < 7 (acidic)
[rainwater: pH = 5.0 to
5.6 normally]
Acid
STATES OF MATTER
1. solid = atoms/molecules in fixed position
a. vibrate around a fixed point
b. has definite shape, definite volume
c. most have crystalline structure = particles arranged
in regular geometric patterns
1) crystals for symmetrical solid objects with flat
faces and straight edges between faces
2) well formed crystals are rare
3) polycrystalline substance = mass of intergrown
crystals
d. glass = molten material cooled
so quickly atoms do
not have time to arrange
2. liquid = atoms/molecules free to move
a. remain close as change positions
b. has no definite shape, but has definite
volume
c. usually takes the shape of the container
3. gas = atoms/molecules move freely and independently
a. particles are farther apart and move
faster
b. formless collection of particles that
tends to expand in all directions at once
c. has no definite shape, no definite volume
4. plasma = composed of ions and electrons
a. higher energy than gas
b. most matter in universe is in this state
c. exist at very high temperatures
Ex: sun and other stars
Changing the state of matter:
1. freezing point = liquid → solid
2. boiling point = liquid → gas
3. melting point = solid → liquid
4. evaporation (vaporization) = liquid changes to
a gas gradually at temperatures below the
boiling point
a. can occur at any temperature
b. much slower than boiling
c. considered a cooling process
5. condensation = when a gas changes to a liquid
a. gas will condense when cooled to its boiling point
or below
b. can occur when gas comes in contact with a cool
surface
c. occurs at the condensation point
d. considered a warming process
6. sublimation = solid changes directly into a gas
without going through the liquid phase
Ex: dry ice
7. deposition = gas or vapor changes directly into solid
without changing to a liquid
Ex: frost
State of matter determined by:
1. attraction between atoms / molecules
2. rate of movement
Can change state by changing:
1. temperature - different for different
substances
2. increase or decrease the pressure
Two Types of Properties
1. physical properties = characteristics that can be
observed without changing composition of
substance
a. includes density, color, hardness, freezing point,
boiling point, ability to conduct electricity, etc.
2. chemical properties = characteristics that describe
how a substance interacts with other
substances
a. produce different kinds of matter
b. includes: interaction with oxygen, being
nonreactive
Ex: iron and oxygen interact to create rust
Conservation of Matter and Energy
1. law of conservation of matter = matter
cannot be created or destroyed but can
change from one form to another
2. law of conservation of energy = energy
cannot be created or destroyed cut can
be changed from one form to another
[First law of Thermodynamics]