Lavoisier

1
(No Transcript)
2
History of the Atom and Chemical Foundations

• Lavoisier
• The law of conservation of mass/matter says that
  the mass of a closed system will remain constant,
  regardless of the processes acting inside the
  system.
• Matter cannot be created/destroyed, although it
  may be rearranged.
• Any chemical process in a closed system, the mass
  of the reactants must equal the mass of the
  products.

Married a 14 year old when he was 28! Beheaded at
the age of 50 during the French Revolution
3
Law of Definite Proportionspublished by Proust
in 1799
History of the Atom and Chemical Foundations

• It was originally argued that compounds could
  combine in any ratio. There was no fundamental
  understanding of mixture and chemical compound
• Proust-
• Used artificial made copper carbonate (CuCO3)
  and comparing it to naturally found copper
  carbonate. showed they had the same proportion
  between the three elements (Cu, C, O)

4
John Dalton
History of the Atom and Chemical Foundations
Dalton's Atomic Theory

• Elements are made of tiny particles called atoms.
  
• All atoms of a given element are identical.
• The atoms of a given element are different from
  those of any other element the atoms of
  different elements can be distinguished from one
  another by their respective relative weights.
• Atoms of one element can combine with atoms of
  other elements to form chemical compounds a
  given compound always has the same relative
  numbers of types of atoms.
• Atoms cannot be created, divided into smaller
  particles, nor destroyed in the chemical process
  a chemical reaction simply changes the way atoms
  are grouped together.

A lunar crater is named after Dalton! And the
Atomic Mass Unit is also known as a Dalton (Da)
5
JJ Thompson

• Cathode Ray Tube- helped establish the identity
  of the electron

Gives off electrons
Vacuum
Magnet - redirected the electrons- nobody knows
why the magnetic field bends
6
Original Model of the Atom

• Plum Pudding Model

An atom made of thousands of electrons would have
a very high, negative electric charge. This was
not observed, as atoms are usually uncharged. In
1906 Thomson suggested that atoms contained far
fewer electrons, a number roughly equal to the
atomic number. This is only one electron in the
case of hydrogen, far fewer than the thousands
originally suggested. These electrons must have
been balanced by some sort of positive charge.
The distribution of charge and mass in the atom
was unknown. Thomson proposed a 'plum pudding'
model, with positive and negative charge filling
a sphere only one ten billionth of a metre
across. This plum pudding model was generally
accepted. Even Thomson's student Rutherford, who
would later prove the model incorrect, believed
in it at the time.
These newly discovered electrons must have been
balanced by some sort of positive charge.
Thomson proposed a 'plum pudding' model, with
positive and negative charge filling a
sphere. Even Thomson's student Rutherford, who
later proved model incorrect, believed it at the
time.
7
Rutherfords Gold Foil Experiment
Expected- particles to go straight through the
plum pudding with its diffuse positive charge
Actual- some particles bounced back! 1 in 8000,
8
Gold Foil Experiment Modified the Model of the
atom Rutherford Model
Often referred as the planetary model- now also
considered incorrect
9
Bohr Model of the Atom
1913-Bohr speculated that electrons orbit around
the atomic nucleus. Electron orbits were at a
fixed distance from the nucleus and had definite
energy. The electron was said to travel in a
fixed-energy orbit that was referred to as an
energy level.
10
Electromagnetic Spectrum
Visible light spectrum portion of whole spectrum
High energy waves
Low energy waves
When you add energy.
Emission Spectra of Fe (atomic number 26) Lots of
electrons!
11
Emission Spectra Supports the Bohr Model