April 3, 2014
The Atomic Theorists
Democritus (460 BCE – 370 BCE)
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Developed the idea of atom (from the word atomos, meaning indivisible)
He thought different “things” were made of atoms that have different shapes
A competing theory: Aristotle (384 BCE - 322 BCE)
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Aristotle (a famous philosopher) proposed that matter was made of different
amounts of these elements: earth, water, fire, air
People believed Aristotle simply because he was more respected and thus
Democritus’ idea was ignored for many years
John Dalton (1766 – 1844 ) [Billiard Ball Model]
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John Dalton performed experiments that led to the acceptance of the idea of atoms
Matter consists of indivisible atoms
Draw Dalton’s model below:
J. J. Thompson (1856 – 1940) [Plum Pudding Model]
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In 1897, Thomson showed that atoms contained even smaller particles using a
cathode ray tube
He proposed the “plum pudding model” where negative charges (electrons) are
scattered throughout a positive atom
Draw Thompson’s model below:
Ernest Rutherford (1871 – 1937) [Planetary Model]
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In 1908, Ernest Rutherford showed that atoms had a nucleus (positively charged)
surrounded by electrons using the gold foil experiment
Draw Rutherford’s model below:
Niels Bohr (1885 - 1962) [Orbital Model]
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In 1913, Bohr reasoned that electrons had specific, circular orbits rather than being
randomly distributed
Draw Bohr’s model below:
Schrödinger (1887 – 1961)/Heisenberg (1901-1976) [Electron Cloud Model]
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In 1920, Erwin Schrodinger showed that electrons did not orbit the nucleus, but
rather moved around the nucleus in a random (but somewhat predictable) manner
Applying Heisenberg's uncertainty principle helped form the orbitals of the Electron
Cloud.
Draw the Schrödinger/Heisenberg model below:
Next class you will have a quiz on the atomic theorists!
Atomic Number, Atomic Mass
On the periodic table, there is atomic number, atomic symbol, and atomic mass.
Draw how hydrogen appears on the table in the space below and label what the atomic
number, atomic symbol and atomic mass is.
The atomic number for sodium is 11. Looking at the periodic table we can see that:
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Sodium has ___________ protons in its nucleus.
Any atom with __________protons is sodium.
A sodium ion has a charge of ______.
Atomic sodium has __________electrons.
If electrons are added or subtracted from a neutral atom, the resulting particle is an
_________.
Electrons are negatively charged, so when an electron is added, it produces a ____________ ion,
also known as a(n) ____________. When an electron is subtracted, it produces a ____________ ion,
also known as a(n) ____________.
How many electrons does N3- have?
Since we know that Atomic mass = # protons + # of neutrons, and that Atomic number = #
of protons, we also know:
# of neutrons = ________________________ - ________________________
Isotopes
Isotopes are atoms of the same element that contain a different number of ____________ .
There are 3 special isotopes that are given special names
Hydrogen – 1 is called protium
Hydrogen – 2 is called deuterium
Hydrogen – 3 is called tritium