Atomic Theory Flashcards
Atoms
Small, hard, indivisible particles mad up of the same material but in different shapes and sizes
Democritus theory
Matter cannot be divided into smaller pieces continuously … Theory was ignored and forgotten
Atomos
Smallest piece, meaning “not to be cut”, changes in matter result from arrangement of grouping of atoms
Aristotle and Plato’s theory
Everything is made up of earth, air, fire, and water .. WRONG
Law of definite proportion
Joseph Proust… Elements composition of a pure substance never varies
John Dalton **
Theory that atoms are building blocks of matter
Bullard ball model
Theorized atoms were like Bullard balls - a single solid mass
Democritus
Matter that was composed of empty space
John dalton postulates
1- atoms of the same element are identical in mass and other properties -INCORRECT
2- chemical reactions occur when atoms are separated, joined, or rearranged. However elements never change into other elements
3- atoms chemically combine in simple whole number ratios to form compound
J.J. Thompson
Plum pudding model… Cathode ray
Plum pudding model
- Negative electrons (plum)
were embedded in a uniform sphere with a positive charge (pudding) - streams if negatively charged particles were found to emanate energy from cathode ray
Cathode ray
Able to measure charge - to - mass ratio to find the mass of a single cathode ray particle
Millikan
Determined charge of electron… Was within 1% of the accepted value (-1) … Used charged and charge to mass ratio to determine mass
Mass of electron
9.11 x 10^(-28) g = 1/1840 of hydrogen atom
Fraction of mass of proton/ neutron
Radioactivity
Spontaneous emission of radiation by an atom … First observed by Henri Becquerel