H Chemistry: Unit 3 Flashcards
Democritus (400 B.C.)
-matter is composed of empty space through which atoms move
-atoms are solid, indestructible, and indivisible
-different properties of matter are due to different types of atoms
-changes in matter result from changes in the groupings of atoms
-discredited by Aristotle
John Dalton (1800)
-all matter is composed of atoms
-all atoms of a given element are identical
-atoms cannot be created or divided
-atoms combine in simple whole numbers to form compounds
-atoms are rearranged in chemical reactions
-atoms are divisible into subatomic particles
-atoms of the same element can have slightly different masses
atom
smallest particle of an element that retains all the properties of the element
Irving Langmuir (1881)
-established the size of an atom
-american scientist
size of an atom
1 billionth of a meter in diameter
Sir William Crookes (1820)
invented the cathode ray
cathode ray
glass tube hooked to a vacuum pump that is hooked up to two different charged electrodes
cathode
negative
anode
positive
J.J. Thomson (1890s)
-performed experiments with the cathode ray tube using magnets and found the negatively charged particles to be smaller than the atom
-credited for discovering electrons
plum pudding atomic model
negatively charged electrons are distributed throughout positively charged matter; sphere
Robert Milikan (1909)
-calculated the actual charge of the electron
-determined the mass of the electron
mass of the electron
9.1 x 10 ^-28 g
Ernest Rutherford (1911)
-gold foil experiment
-credited for discovering the nucleus of the atom and the proton
-nuclear model
gold foil experiment
where a narrow beam of positively charged alpha particles pass through a thin piece of gold foil and were reflected on a zinc sulfide screen
James Chadwick (1932)
discovered the neutron and that it has mass equal to that of a proton
Niels Bohr (1920-1940)
-improved Rutherford’s model by placing electrons at specific energy levels
-Bohr’s model
atomic number
indicates the number of protons
proton
positively charged subatomic particle located in the nucleus
-identifies the atom
-not gained or lost naturally in the lab
electron
negatively charged subatomic particle that orbits the nucleus
-determines reactivity
-number is the same as number of protons if atom is neutral
ion
charged atom from the gain or loss of electrons
anion
negatively charged ion from the gain of electrons
cation
positively charged ion from the loss of electrons
atomic mass
indicates the number of protons and neutrons together
-units are amu
mass of a proton/neutron
1 amu
neutron
neutrally charged subatomic particle in the nucleus of an atom
-calculated by taking the atomic mass and subtracting the atomic number