Honors Chemistry - Unit 2: Atoms, Isotopes, Periodic Table

honors chemistry semester 1, unit 2.

Democritus

around 400 BC, proposed that matter was made of small, hard, and indivisible particles called atoms. no real evidence, not widely believed

Dalton

1803-1808. defined atom. atom was indivisible, and matter is made of atoms. atoms of one element are identical.

Thomson

1904. “Plum Pudding” model of the divisible atom. discovered the existence of the electron.

Rutherford

1911. gold foil experiment. atom had a very small, positively charged nucleus containing most of the mass. electron # = proton # and electrons move around the nucleus.

Bohr

1913. “Planetary” model. electrons move around the nucleus in fixed orbits. electrons can move to different orbits based on energy level.

Present

electrons occupy orbitals which are volumes of space around the nucleus. different energy levels and sublevels which contain sets of orbitals.

matter

anything that has mass and takes up volume

physical properties

a characteristic of a substance that can be seen or observed without changing the identity of the substance

chemical properties

describes the ability of a substance to undergo a specific chemical change

chemical property ex.

corrosiveness, rusting, acidity, toxicity, flammability

physical property ex.

color, odor, melting & boiling point, density, taste

element

a pure substance that cannot be broken down further than it is

compound

two or more elements chemically combined. the elements lose their identities and take on new properties.

mixture

two or more substances physically combined together

Law of Conversion of Matter

matter cannot be created or destroyed, only changed.

physical change

changing the form of particles without changing what the substances are made of. usually reversible

physical change ex.

melting, evaporating, condensing, freezing

chemical change

two or more different substances combine/break apart to form a new, different substance. usually NOT easily reversible. 

atom

basic unit of an element that still retains the properties of that element

atomic number

the number of protons in the nucleus

atomic mass

number of protons and neutrons in the nucleus

isotope

same element but a different number of neutrons/mass

average atomic mass

weighted average mass of an atom based on abundance.

valence electrons

electrons in the outer most energy level/shell which are involved in bonds and reactions

ions

atoms without a charge

octet rule

all atoms “want” 8 valence electrons

duet rule

1st energy level has 2 electrons

cation

PAWsitively charged atom (lost electrons)

anion

onions = tears. negative charged atom (gained electrons)