chemistry: matter and chemical bonding early atomic theories
TRANSCRIPT
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 Particle
Charge Location Size
Proton (p+) Positive Nucleus 1
Neutron (n0) Neutral Nucleus 1
Electron (e-) Negative In Orbit 1_ 2000
Atomic mass / Mass Number-Use rounded values
-26.98 -> 27-28.09 -> 28-30.97 -> 31
Atomic Number= # of protons= # of electrons in a neutral atom
Mass number = protons + neutrons
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
mass # is 12 atomic # is 6 therefore, this carbon has 12 - 6 = 6
neutrons
6
12
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