chem atom scientists

democritus

matter is discontinuous (i.e., "grainy"), "atomos" = uncuttable or indivisible, coined the word "atom"

greek model of atom

proposed by democritus, looks like a sphere, solid and indestructible

aristotle

did not agree with democritus, believed "matter is continuous"

antoine lavoisier

law of conservation of mass

law of conservation of mass

matter is neither created nor destroyed during ordinary chemical reactions or physical changes; the total mass of the reactants must equal the total mass of the products

joseph proust

law of definite proportions

law of definite proportions

a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound

john dalton

law of multiple proportions, atomic theory

atomic theory

1. elements are made of indivisible particles called atoms (wrong)
2. atoms of the same element are exactly alike; in particular, they have the same mass (wrong)
3. compounds are formed by the joining of atoms of two or more elements in fixed, whole-number ratios

dalton's model of the atom

solid sphere, like democritus

amu

unit used to measure mass of atoms

atomic number

number of protons

mass number

protons + neutrons

anion

negative ion

cation

positive ion

isotopes

atoms of the same element that have different numbers of neutrons

jj thomson

discovery of first subatomic particle (electron) via cathode ray (a power source was attached to two metal ends of an evacuated glass tube, called a cathode ray tube, a beam of "light" appears between the two electrodes called a cathode ray)

robert millikan

calculated the mass to charge ratio of an atom through millikan oil drop experiment, found that e- mass is almost nonexistent

thomson's atomic model

electrons of the atom were embedded in a positively charged ball-of-matter, which led to the name "plum-pudding model"; this model kept dalton's ideas intact

rutherford's gold foil experiment

involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick); most passed through the sheet without changing course (= atoms are mostly open space), some bounced away from the gold sheet as if they had hit something solid (= nucleus is positively changed, has most mass of the atom, has protons)
invalidated plum pudding model

rutherford's model

nucleus is positively charged, e- orbit around nucleus, aka nuclear model

james chadwick

discovered the neutron (electrically neutral, mass nearly equal to proton)

niels bohr

discovered that electrons exist in several distinct layers or levels, travel around nucleus like planets travel around sun, travel only in successively larger circular orbits, can jump between levels with energy being added/released

planetary model

suggested by niels bohr, looks like a solar system; influenced by max planck's ideas to explain what keeps the negatively charged electrons from moving into the positively charged nucleus

max planck

when matter is heated, it gives off specific wavelengths of energy (known as quanta), which means electrons can only exist at specific energy levels

quantum mechanical model

heisenberg, schrodinger, de Broglie; electrons live in fuzzy regions or "clouds", not distinct orbits; electron location can not be predicted

de Broglie

discovered that electrons act like waves (wave-particle duality); matter acts like a particle AND a wave; frequencies of electrons correspond to the energy levels around the nucleus

uncertainty principle

heisenberg; we can't know EXACTLY where an electron is or how fast it's moving