SNC1D0 Atomic History
Transcript SNC1D0 Atomic History
Matter and Chemical Bonding
Early Atomic Theories
Timeline. . . . .
Ancient Greeks (approx 450 BC)
"Four Element" Theory – Earth, Air, Fire,
First suggestion that substances were
actually made up of a combination of
400 BC – Democritus
"The smallest indivisible particle of
matter is the 'atom' "
No evidence – based on thought
However, the "4 element" theory
lingered for almost 2000 years!
John Dalton (1809)
All matter is composed of indivisible
particles called atoms.
All atoms of a given element are identical;
atoms of different elements have different
Chemical reactions involve the combination
of atoms, not the destruction of atoms.
When elements react to form compounds,
they react in whole-number ratios.
Dalton's atomic theory supported previous
research. Lasted almost a century!
Model: Indivisible billiard ball
J.J. Thomson (1897)
Used the work of other scientists that
showed that atoms contain charges,
and his own work with cathode ray
tubes, to develop a modified atomic
Atoms are positive spheres, with
negative particles (electrons)
embedded in them.
Model: Raisin bun
Ernest Rutherford (1911)
Student of Thomson – disagreed.
Gold Foil Experiment:
Alpha radiation (positive) were shot at a
piece of gold foil.
Most of the alpha particles passed through
the foil, suggesting that most of matter is
Some particles were deflected back at
angles; they had come in contact with
something very dense!
Gold Foil Experiment:
Leading to…..Nuclear Model:
Rutherford – dense core of positive
charge (nucleus), with negative
electrons orbiting around the nucleus.
Later experiments showed that the
positively charged particles, now
called protons, have an equal but
opposite charge to the electrons, and
have a mass 1836 x greater!
The neutron and the existence of
isotopes were also discovered
Worked with Rutherford
Used atomic spectrum information to
place electrons in energy levels
around the nucleus
How it works….
Each element has a unique emission
When electrons are given energy,
they jump to a new energy level
When they fall back down, they emit
this extra energy as light
Lines on an emission spectrum
represent jumps between energy
Modern View of the Atom
Dense nucleus containing:
Shells of small (-) electrons orbiting
2 e- in 1st orbital
8 in 2nd
8 in 3rd
(until next year)
Neutron (n0) Neutral
Electron (e-) Negative In Orbit
= # of protons
= # of electrons
in a neutral atom
Atomic mass / Mass Number
-Use rounded values
-26.98 -> 27
Mass number = protons + neutrons
-28.09 -> 28
-30.97 -> 31
Atoms of the same element have the same #
The # of neutrons can differ
The same element with a different # of
neutrons are called isotopes
Radioisotopes are unstable and decay
Average atomic mass takes the masses of all
isotopes into account.
Standard Atomic Notation
mass # is 12
atomic # is 6
therefore, this carbon has 12 - 6 = 6
GROUPS ON THE
Subatomic Particle Worksheet
Define: Chemical Family, Periods, Dmitri
“Try this” on page 224
P. 225 Q: 1-6, 8-11