Atomic theory and the periodic table

1
Atomic theory and the periodic table
2
Current model of the atom a 3-D view of the atom
3
How did we get to this point?
4
Democritus or Leucippus

• Democritus was a student of Leucippus and
  co-originator of the belief that all matter is
  made up of various imperishable, indivisible
  elements which he called atoma (sg. atomon) or
  "indivisible units", from which we get the
  English word atom.

5
Aristotle
6
Did he agree with the theory of atoma?

• NO He believed in the idea that matter
  consisted of 4 basic elements Earth, Air, Water,
  and Fire. This was stated as part of his
  Doctrine of four elements.

7
Who did the people believe?

• Because of his political influence and the
  influence of the church, many believed in the
  ideas of Aristotle for the next 2000 years. They
  followed what we now call Aristotelian
  philosophy.

8
John DaltonSeptember 6, 1766 July 27, 1844)
9
What did Dalton do?

• Dalton loved meteorology. Much of what he
  understood about matter was a result of his
  studies in this field.
• He arrived at Daltons Law of Partial pressures
  that stated that if you have a mixture of gases
  in a container, the total pressure was the sum of
  the individual partial pressures of the gas.
• He was able to calculate atomic weights (that
  were later used to develop the first periodic
  table).

10
What was Daltons ,most significant contribution?

• John Dalton, in 1803, developed the first Modern
  Atomic Theory. This law had several components
• All matter is made up of atoms that are in
  continual motion and not capable of being
  sub-divided.
• The reason a form of matter is pure is pure is
  due to the fact that all atoms that make up that
  substance are identical.
• Atoms of different elements are different from
  each other.
• Compounds have constant composition because they
  have a fixed ratio of atoms.
• Chemical reactions involve a rearrangement of
  atoms.

11
John Joseph Thomson(1856-1940)
12
How did Thomson help to contribute to our
understanding of the atom?

• Using a high vacuum cathode-tube (see next slide)
  and electrical current, Thomson realized that
  there must be bodies must smaller than atoms
  that had a negative charge. He called these
  little bodies corpuscles that were later
  renamed electrons.
• This was significant in that it proves that there
  are lighter forms of matter than atoms.

13
What is a cathode-ray tube
14
Ernest Rutherford(1871-1937)
15
What were his contributions to our understanding
of the atom?

• He was a research student working under Thomson
  while at the Cavendish Laboratory.
• In 1911, using alpha particles (positively
  charged form of radiation), he concluded that the
  atom is not a positive particle with negatively
  charged electrons just randomly scattered about
  as Thomson suggested in his Plum Pudding model
  of the atom.
• In 1916, he states publicly that he hoped
  mankind should not discover how to extract the
  energy from the nucleus until man was living at
  peace with his neighbour

16
Robert Millikan(1868 1953)
17
What were Millikans contributions to our
understanding of the atom?

• In 1910, using the famous oil-drop experiment,
  he determined that all electrons in atoms had a
  fixed charge. Using some mathematics, he also
  calculated the charge of the electron.
• Between 1912 and 1915, he made the first direct
  photoelectric determination of Planck's constant,
  h.

18
The Oil-Drop experiment
19
Neils Bohr(1885-1962)
20
What were Bohrs contributions to our
understanding of the atom?

• He was a research student working under
  Rutherford.
• In 1913 Bohr published a theory about the
  structure of the atom based on an earlier theory
  of Rutherford's. Rutherford had shown that the
  atom consisted of a positively charged nucleus,
  with negatively charged electrons in orbit around
  it. Bohr expanded upon this theory by proposing
  that electrons travel only in certain
  successively larger orbits. He suggested that the
  outer orbits could hold more electrons than the
  inner ones, and that these outer orbits determine
  the atom's chemical properties.

21
Daltons model of the atom (similar to the early
Greeks)
22
J.J. Thomsons model of the atom
23
Rutherfords model of the atom
24
Revised Rutherford model
25
Bohrs Model of the atom
26
Current model of the atom
27
How did we get the periodic table we use today?

• Scientists are always trying to organize and
  classify facts to try to look for trends. This
  is true in any scientific field. (The
  classification of matter is just one example).
• Classifying the elements is no different.
• So how did the table get the look it has today?

28
1st attempt to organize the elements!

• Triads an idea of Johann Dobereiner that groups
  elements in sets of three such that the average
  mass of the 1st 3rd elements have a mass
  equivalent to the middle element.
• Click here to see a website below to see a good
  explanation of this.
• This idea was a forerunner for the idea of
  groups!

29
2nd attempt to create a periodic table

• Law of Octaves an idea of John Newlands that
  involves simply grouping the known elements into
  sets of 8 with increasing atomic mass.
• For an example of this, lets complete the
  Octaves Activity!

30
3rd attempt a successful attempt.

• This attempt resulted in the 1st published
  periodic table. This table arranged the known
  elements in order of increasing atomic mass while
  grouping elements according to similar
  properties. This table had blanks in it to allow
  for elements not yet discovered!
• Dmitri Mendeleev was responsible for this tabloe
  in 1869!

31
(No Transcript)
32
How was that table different than ours of today?

• The elements were arranged by increasing atomic
  mass todays is arranged by increasing atomic
  number (number of protons).
• 2) The elements with similar properties were in
  rows (series) of elements todays they are in
  columns (groups).