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 = 2e-
3rd level = 18 e-
2nd level = 8e-
4th level = 32 e-
2. 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 e- easily 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+, Clb. 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)
c. pH < 7 (acidic)
[rainwater: pH = 5.0 to
5.6 normally]
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