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18 Cards in this Set

  • Front
  • Back
Where did the idea of the atom originate?
Ancient Greeks thought that there might be a smallest particle of matter (2400 years ago)
Who is John Dalton?
Explored chemical observations in 1800s with atoms that he believed were like tiny marbles
Who was JJ Thomson?
Discovered electrons in 1900s
What was Rutherford's experiment?
Rutherford fired a beam of positively charged alpha particles at a very thin piece of gold foil. He expected them to pass right through. The particles appeared as tiny flashes of light on the fluorescent screen. However, the boundary of the circle formed by the flashes was fuzzy, which meant that some particles had been deflected. A few even bounced back from the foil. He concluded that an atom is mostly empty space with a positively charged center.
What does Rutherford's experiment tell us?
1. The center of an atom contains a concentrated positive part (nucleus) and protons BECAUSE some particles bounced back (repelled.)
2. Electrons are scattered tiny negative particles scattered in a cloud outside nucleus BECAUSE some of the beam was only slightly changed so whatever was there was tiny and spread out.
Who was Chadwick?
Proved the existence of neutrons
(charge, location, weight, etc.)
in nucleus
1800 * heavier than electron
# determines element
(charge, location, wieght, notes)
no charge
1800 * heavier than electron
# neutrons can vary
cloud outside nucleus
very tiny and light
always equals # protons to start
How are electrons arranged?
Electrons are arranged so that they balance the attraction to the nucleus vs. the repulsion between each other
What are shells?
Shells are clouds, or spheres, around the nucleus
How does the size of a shell matter?
The bigger the shell, the more electrons it can hold before repulsion takes over
On what does the chemical behavior of an atom depend?
The valence, or outermost, shell
How do we group elements?
In families depending on chemical behavior, listing smallest atomic number to largest
atomic number
number of protons in an atom
atoms with the same atomic number but different neutrons
As you go across the row of periodic table...
number of electrons in valence increases
As you go down a column...
the number of shells increases