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 each3. periodic table = system for classifying

elements4. most abundant elements in universe =

hydrogen & helium5. 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 STRUCTURE1. 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 electrons2. unique to each element3. when number of p+ equals the number of

e- → atom is neutral4. if number of p+ change → new element

mass number = number of p+ and n in nucleus1. measured with special unit called atomic

mass unit (u)2. * increase in mass as number of p+ and n

increase3. 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 levels3. outermost level can never hold more than 8e-

a. 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 element5. 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 element2. atomic mass = average of mass numbers of all

isotopes of an element3. 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 Atoms1. 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 BONDS1. 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 electrons2. 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 present2. indicates how many atoms of each element are

present3. symbol itself indicates one atom is present4. subscript = number used after the symbol to tell how

many atoms of an element are present if there are two or more

Ex: H2OH (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 means2. heterogeneous mixture = components are easily

recognizable Ex: soil3. 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 soil2. 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]

Acid

Base

STATES OF MATTER1. 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 container3. 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 volume4. 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 → solid2. boiling point = liquid → gas3. melting point = solid → liquid4. 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 phaseEx: 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 / molecules2. rate of movement

Can change state by changing:1. temperature - different for different

substances2. increase or decrease the pressure

Two Types of Properties1. 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

nonreactiveEx: iron and oxygen interact to create rust

Conservation of Matter and Energy1. 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]