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Home , Atom, Atomic theory, History of chemistry

4.01 Evolution of the

Atomic

The Events Leading to the Discovery of the Building Block of

Dr. Fred Omega Garces 152 Miramar College

1 401 Atomic Evolution 05.2015 Idea of the

How did man come up with the idea of the atom ?

It took ~2400 years from when it was conceived to the time experimental evidence prove of the atom existence.

2 401 Atomic Evolution 05.2015 and development of the atomic model

History of Atomic Structure The timeline of the progression of the development of the Modern .

Atomic Theory Timeline

J.

Empedocles J. Proust A. Lavoisier

R. Boyle

Zeno Aristotle Democritus Boyle Lavoisier Dalton

R. Bacon

-5 0 0 -2 5 0 0 2 5 0 5 0 0 7 5 0 1 0 0 0 1 2 5 0 1 5 0 0 1 7 5 0 2 0 0 0

3 401 Atomic Evolution 05.2015 Matter according to ... Greek Philosophers

492-375 BC: (supported by Aristotle) ---

400 BC: Zeno (also supported by Aristotle) Matter can be infinitely divided

400 BC: Leucippus 470-375 BC: Democritus (student of Leucippus) Proposed the idea of the atom Matter -indivisible called

4 401 Atomic Evolution 05.2015 Next 2000 Years (pseudo ) into experiments ( magic) took detailed notes (lab notebook conceived) Systematic (extracted from )

Roger Bacon (1214-1292) An English and alchemist, Bacon became known as the founder of experimental science. He believed that doing experiments for yourself rather than just accepting what other people tell you was the way to learn about . His most important work was the Opus Matus, in what he wrote about the of learning. He did many experiment which showed how rainbow are made by the effect of water drops on sunlight and how lenses could be used to help people with weak sight.

5 401 Atomic Evolution 05.2015 Atomic Structure Revolution 1500 The Skeptical He performed detailed experiment with ; this initiated the break down of the Greek's model of matter.

1700 Father of modern chemistry (Law of conservation of )

He made very careful measurements and concluded that mass is neither created nor destroyed. The thought at the time was then when a substance was burned, the ashes were lighter than the starting material, but Lavoisier did the experiment in an enclosed container and determined that the mass did not change. Subsequent experiments with other reactions was consistent with the findings.

6 401 Atomic Evolution 05.2015 1790-1800 Joseph Proust (Law of definite proportion or Law of constant composition) A given compound always contain exactly the same proportion of elements by mass.

i.e., H2O 2:16 or H : O 1 : 8 by mass always true whether there is 18 g or 139 g H2O

For, H2O2 2:32 the H : O is 1 g H : 16 g O

In other words, Water found in SD or the Arctic or Jupiter’s moon will all have 1 g to 8 g ratios. Likewise found in cane or sweet beets have 6 g to 1 g hydrogen to 8 gram oxygen ratios (12 x 6 C: 1 x 12 H: 16 x 6 O). i.e.,The relative numbers and kinds of atoms are constant.

7 401 Atomic Evolution 05.2015 1800 J. Dalton: Founder of the Modern Atomic Theory (Law of Multiple proportion) When two elements form a series of compounds, the ratio of the of the element that combine with 1 gram of the first element can be reduce to small whole numbers.

Example: : Mass of that combines with 1.0 gram of oxygen *Compound A 1.750 g g A/B = 1.750/0.8760 = 2 / 1 Compound B 0.8750 g g B/C = 0.8760 / 0.4375 = 2 / 1 Compound C 0.4375 g g A/C = 1.750 / 0.4375 = 4 / 1

Compounds consist of atoms which combines in whole number ratios.

*N2O g N2O NO g NO NO2 g N1/2 O

8 401 Atomic Evolution 05.2015 1808 Dalton's Atomic Theory :

A new system of Chemical • All matter is made of atom.

• In a atoms are neither created or destroyed but only arranged differently.

• Atoms of the same element are identical.

• Atoms of different elements are not the same.

• Compounds are formed from two or more atoms. A given compound always has same relative number and type of atoms.

9 401 Atomic Evolution 05.2015 ... what’s next ??

Around this period, the model of the atom was gaining acceptance by scientist.

Questions still unanswered -

What is an atom?

How is it put together?

What are the parts of an atom?

10 401 Atomic Evolution 05.2015 Early experiments to characterize the atoms

The parts: - Thomson (1904), Millikan (1909) - Goldstein (1886) Rutherford (1911) - Sir (1932)

11 401 Atomic Evolution 05.2015 Faraday ~1832 Contributions to the Modern Atomic Theory

Balmer Mendeleev Michelson Discharge Tubes C The modern Atom: a flow chart ~ 1830 - 90 ~1870 ~1885 of major theoretical and Becquerel, Curie Thomson Planck Radioactivity α,β γ experimental contributions e/m ~1897 ~1897 ~1900 (who, what, and when) leading to Einstein our understanding of the atom. Millikan Rutherford E=hv, E=mc2 e Nucleus ~1905 ~1909 ~1911

Bohr Scientific discovery is a Shell Model ~1913 complex human endeavor. The Aston developments leading to our ~1909 Stern, Gerlach deBroglie Matter Waves ~1921 ~1924 understanding of the modern atom, dramatically depict Schrodinger scientific discoveries not as Wave Model, Heisenberg Pauli Exclusion, individual efforts, but as the Hund's Rules ~1927 ~1926 collective work of the scientific . Chadwick ~1932

12 401 Atomic Evolution 05.2015 Early experiments to Characterize the atoms

1820's Sir Humphrey Davy / Matter contains negative charge particles (electrons). Later, rays were discovered and in the late 1800's cathode rays was investigated further. (1832)

http://video.google.com/videoplay?docid=4144497206440839046

1900 John J. Thomson Cathode rays were electrically charge particles. tube with electron stream where deflected by positive and negative plate: e / m = -1.76•108 C/g Proposed the ""

theory of the atom; based on 's Law: F = k ( Q1 Q2) / r. Atoms contains protons and electrons.

1909 R.A. Millikan Oil drop expt.: Determine the electron’s charge-value. e- = -1.60•10-19 C m = 9.11 •10-31 kg

13 401 Atomic Evolution 05.2015 Arrangement of subatomic particles

1911 : Gold thin foil experiment. Reflection of alpha radiation on gold foil proved that the atom consisted of a very dense nucleus.

• Based on the particles deflection pattern, Rutherford calculated the fraction of the atomic volume occupied by the positive nucleus of about 1 part in 1014. The mass is so dense that a nucleus the size of a pea would have mass greater that 250 million tons.

14 401 Atomic Evolution 05.2015 Characteristics of Atomic Parts

The parts: Subatomic particles and their properties

Particle Mass *Rel Mass Relative Charge (amu)

e -; electron 9.109•10 -31 Kg 1/1837 - 1.602•10 -19 C

p + ; 1.673•10 -27 Kg 1 + 1.602•10 -19 C

n; neutron 1.675•10 -27 Kg 1 0

* Relative mass: 1 amu = 1 proton

15 401 Atomic Evolution 05.2015 Summary These were a few of the experiments which lead to the discovery and a better understanding to the parts of the atom.

Three sub-atomic particles : electron, protons, and neutrons combine in various numbers and arrangement to make the different 109 elements (and counting) in the periodic table.

The picture of the atomic architecture is now complete (or is it ?).

From the time of Dalton g Thomson g Rutherford g Bohr g Schrodinger, our model of the atom has undergone many modifications. The model is not finish however.

16 401 Atomic Evolution 05.2015 String theory is an active research framework in that attempts to reconcile and general relativity general relativity.[1] It is a contender for the (TOE), a manner of describing the known fundamental and matter in a mathematically complete system. The theory has yet to make testable experimental predictions, leading some scientists to claim that it cannot be considered a part of science.

http://superstringtheory.com/.

http://www.pbs.org/wgbh/nova/elegant/

17 401 Atomic Evolution 05.2015