Unit 3: Atomic THeory Flashcards
which greek philosopher believed in atoms and which philosophers believed that matter is continuous?
Democritus
Aristotle and Plato
What four elements did the ancient greeks think matter was composed of?
Earth, Air, Water, Fire
John Dalton
An english chemist who in 1803 offered ideas about atoms in five statements, combined into Dalton’s Atomic Theory
By when was it accepted that two elements could combine to form a compound, and that pure samples would always have the same composition by mass?
1803
What is the first statement of Dalton’s Atomic Theory?
Matter is composed of extremely small particles called atoms.
Second statement of Dalton’s Atomic Theory?
Atoms of a given element are the same (identical), but different elements have different atoms.
Third statement of Dalton’s Atomic Theory?
Atoms cannot be subdivided, created or destroyed.
Fourth statement of Dalton’s Atomic Theory?
Atoms can combine to form compounds in simple whole number ratios.
Fifth statement of Dalton’s Atomic Theory?
In chemical reactions, atoms are combined, separated, or arranged.
Law of Multiple Proportions
Single whole number ratios that compounds are composed of.
why the 1800s they’d demonstrated that matter also had an…
electrical nature
what did benjamin franklin say about electricity?
that electricity is related to tiny, negatively charged particles
what were electrons named after?
greek word ‘elektron’ meaning amber
atoms are electrically
neutral
when did JJ Thomson experiment with cathode ray tubes?
1897
what was the first discovery of a subatomic particle
jj thomson’s experiments with cathode rays, which he concluded were a stream of negatively charged particles
what did jj thomson (confirmed by rober millikan) demonstrate with his experiments about the electron?
that an electron’s volume was very small in relation to it’s mass
the cathode rays were determined to behave like…
particles
what are the two conclusions made from the thomson cathode experiments?
1) If atoms are electrically neutral there must be a positively charged particle within the atom
2) if atoms have a mass there must be other particles within the atom which contain most of the mass.
what was thomson’s model of the atom called?
plum pudding model
when did rutherford do his gold foil experiment?
1911
explain the gold foil experiment
positive alpha particles were used to bombard a thin piece of gold foil with positively charged alpha particles
what did rutherford expect, if mass and charge were uniformly distributed throughout an atom?
that the alpha particles would pass through with a slight deflection.
conclusions of the gold foil experiment
- most of the atom is empty space
- the atom contains a small dense positive center (the nucleus)
- electrons surrounding the nucleus orbit in a planetary fashion, proposing a planetary model.
results of the gold foil experiment
- most particles passed through Au foil, since atoms are made up mostly of empty space
- very few particles were deflected back towards the source of the alpha particles.
who discovered the neutron?
james chadwick
when and how did chadwick discover the neutron?
in 1932, when he bombarded Be atoms with alpha particles and they emitted an energetic stream of radiation.
why did it take so long for the neutron to be discovered?
- it is neutral, so no charge
- difficult time, the great depression
describe Neils Bohr’s model of the atom
- it placed each electron in a specific energy level
- electrons moved in definite orbits around the nucleus like planets
- these orbits/energy levels are located at certain distances from the nucleus
when did Neils Bohr create his model?
1913
bohr: lowest energy level is closest
to the nucleus
bohr: electrons can move between
energy levels