ATOMIC THEROY Flashcards
atom:
the smallest unit into which matter can be divided without the release of electrically charged particles
*also known as the smallest piece of a pure substance
Who discovered the atom?
-Democritus (400 BC) proposed that if a pure substance were divided into smaller pieces, eventually we would arrive at something so small it would be divided no further
Who discovered the “Billiard Ball Model”?
-John Dalton (1808) proposed the 1st modern model of the atom
Does Dalton’s model have internal parts?
-no because they are featureless spheres
When are compounds created?
-when atoms of different elements join together in definite properties (ex. H20)
What does John Dalton’s Model explain?
- it explains why “chemical reactions” occur in definite properties
- also explains “thermal properties” of matter such as pressure an temperature
What does the “Billiard Ball Model” not explain?
- it does NOT explain the “electrical properties” of matter
* matter has positive (+) & negative (-) parts
Who performed experiments to discover the “Raisin Bun Model” (Plum Pudding) ?
-J.J Thomson performed experiments (1897) to see how positive and negative matter were affected by electric and magnetic force
Does positive or negative parts have smaller mass?
-the negative parts of matter have much smaller mass than the positive parts
Which positive or negative part depend on the element?
-the mass of the positive parts depend on the element (same as Dalton’s model)
Which part will always be the same?
-the negative parts will always be the same; regardless of which element the negative part came from
What are the negative parts called?
-they are called “electrons”
What are the positive parts called?
-they are called “protons”
When was the “Raisin Bun” or “Plum Pudding” proposed?
-in 1904
What does the “Raisin Bun Model” contain?
-the “bun” is a sphere containing most of the atom’s mass
(like the “Billiard Ball”, the size and mass of the atom differ from 1 element to another
What are embedded in the “Raisin Bun Model”?
-there are “electrons” (raisins) embedded in the atom (bun) that have very small mass and a negative charge
Do electrons have all the same properties in the “Raisin Bun Model”?
-different elements have differing numbers of electrons, but the electrons all have the same properties regardless of which element they came from
Who discovered a “thin gold foil”?
“Ernest Rutherford” and his students performed an experiment (1909) where they fired small, high-speed, positive particles at a thin gold foil (“gold” is a large atom)
What are the “alpha particles” passed through?
-most of the “alpha particles” pass through the gold foil with nearly no effect
How many “alpha particles” are deflected by the gold foil?
-a very small percentage
What did Rutherford conclude?
-he concluded that the “Raisin Bun Model” could not explain the results he had
Who discovered the “Planetary (Nuclear) Model?
“Ernest Rutherford” proposed a new model (which is also called the “solar system” or nuclear model) (1911)
What is Rutherford’s model mostly made up of?
-most of the atom is empty space, since the alpha particles were unaffected
What is most of the atom’s mass in the Rutherford’s model?
- most of the atom’s mass is concentrated in a tiny nucleus, which cause some of the alpha particles to deflect
What do the electrons orbit around in the Rutherford’s model?
-the electrons orbit around the nucleus like the planets orbiting the Sun
protons:
have a positive charge (+)
neutrons:
have no charge (-)
What have nearly the same mass?
-protons and neutrons
