Chemistry:
Matter and Chemical Bonding
Early Atomic Theories
Timeline. . . . .
 Ancient Greeks (approx 450 BC)
 "Four Element" Theory – Earth, Air, Fire,
Water
Benefits:
 First suggestion that substances were
actually made up of a combination of
different "elements."
Democritus:
 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!
(YIKES)
Democritus’ Model
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
properties.
 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
theory.
 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
empty space!
 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
Niels Bohr
 Worked with Rutherford
 Used atomic spectrum information to
place electrons in energy levels
around the nucleus
Spectroscope:
How it works….
 Each element has a unique emission
spectrum
 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
levels.
DEMO
Emission Spectra:
Modern View of the Atom
 Dense nucleus containing:
 (+) protons
 Neutral neutrons
 Shells of small (-) electrons orbiting
the nucleus
2 e- in 1st orbital
8 in 2nd
8 in 3rd
(until next year)
Subatomic Charge
Particle
Location Size
Proton (p+)
Positive
Nucleus
1
Neutron (n0) Neutral
Nucleus
1
Electron (e-) Negative In Orbit
1_
2000
Atomic Number
= # 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
Isotopes
 Atoms of the same element have the same #
of protons
 The # of neutrons can differ
 The same element with a different # of
neutrons are called isotopes
 Radioisotopes are unstable and decay
creating radioactivity
 Average atomic mass takes the masses of all
isotopes into account.
Standard Atomic Notation
C
12
6
 mass # is 12
 atomic # is 6
 therefore, this carbon has 12 - 6 = 6
neutrons
GROUPS ON THE
PERIODIC TABLE
Your Turn
 Subatomic Particle Worksheet
 Read 6.4
 Define: Chemical Family, Periods, Dmitri
Mendeleev
 “Try this” on page 224
 Homework
 P. 225 Q: 1-6, 8-11