History of the Atom

1. History of the Atom Scientists and Their Contribution to the Model of an Atom Adapted from Mr. Jones’s Science Class and GLENCOE ppt (accompanied school textbook) Heaton Fall 2013

2. History of the Atom - Timeline Antoine Lavoisier makes a substantial number of contributions to the field of Chemistry J.J. Thomson discovers the electron and proposes the Plum Pudding Model in 1897 Niels Bohr proposes the Bohr Model in 1913 James Chadwick discovered the neutron in in 1932 1766 – 1844 1871 – 1937 1887 – 1961 460 – 370 BC 1700s 1800s 1900s 0 Erwin Schrodinger describes the electron cloud in 1926 Democritus proposes the 1st atomic theory John Dalton proposes his atomic theory in 1803 Ernest Rutherford performs the Gold Foil Experiment in 1909 1891 – 1974 1743 – 1794 1885 – 1962 1856 – 1940 Click on picture for more information

3. Democritus(460 BC – 370 BC) • Proposed an Atomic Theory(along with his mentor Leucippus) which states that all atoms are particles that are: • Small, Hard, Solid • Homogenous • *Indivisible • *Indestructible • Space exist between each “atomos” • made of a single material formed into different shapes and sizes. • Aristotle did not support his atomic theory Image taken from: https://reich-chemistry.wikispaces.com/T.+Glenn+Time+Line+Project

4. Aristotle(484 BC – 322 BC) • Aristotle opposed atomic theory- did not believe in the existence of atoms • Believed all mater was composed of • Earth, Water, Fire and Air • Empty space cannot exist • Believed all mater was endlessly divided into smaller and smaller pieces (https://www.youtube.com/watch?v=cnXV7Ph3WPk) • Student of Plato and mingled with Alexander the Great

5. Antoine Lavoisier(1743 – 1794) • Known as the “Father of Modern Chemistry” • Was the first person to generate a list of thirty-three elements in his textbook • Devised the metric system • Was married to a 13-year old Marie-Anne Pierette Paulze; she assisted him with much of his work • Was a tax-collector that was consequently guillotined during the French Revolution • Discovered/proposed that combustion occurs when oxygen combines with other elements • Discovered/proposed the Law of Conservation of Mass (or Matter) which states, in a chemical reaction, matter is neither created nor destroyed Image taken from: www.ldeo.columbia.edu/.../v1001/geotime2.html

6. John Dalton (1766 – 1844) • In 1803, proposed an Atomic Theory which states: • All substances are made of atoms; atoms are small particles that cannot be created, divided, or destroyed. • Atoms of the same element are exactly alike, and atoms of different elements are different • Atoms join with other atoms to make new substances • Calculated the atomic weights of many various elements • Was a teacher at a very young age • Was color blind Image taken from: chemistry.about.com/.../John-Dalton.htm

7. A • B • C • D Who was the first person to propose the idea that matter was not infinitely divisible? A.Aristotle B.Plato C.Dalton D.Democritus

8. A • B • C • D Dalton’s theory also conveniently explained what? A.the electron B.the nucleus C.law of conservation of mass D.law of Democritus

9. J.J. Thomson (1856 – 1940) • Proved that an atom can be divided into smaller parts • While experimenting with cathode-ray tubes, discovered corpuscles, which were later called electrons • Stated that the atom is neutral • In 1897, proposed the Plum Pudding Model which states that atoms mostly consist of positively charged material with negatively charged particles (electrons) located throughout the positive material • Won a Nobel Prize Image taken from: www.wired.com/.../news/2008/04/dayintech_0430

10. J.J. Thomson (1856 – 1940) Cathode Ray Tube

11. Ernest Rutherford (1871 – 1937) • In 1909, performed the Gold Foil Experiment and suggested the following characteristics of the atom: • It consists of a small core, or nucleus, that contains most of the mass of the atom • This nucleus is made up of particles called protons, which have a positive charge • The protons are surrounded by negatively charged electrons, but most of the atom is actually empty space • Did extensive work on radioactivity (alpha & beta particles, gamma rays/waves) and was referred to as the “Father of Nuclear Physics” • Won a Nobel Prize • Was a student of J.J. Thomson • Was on the New Zealand $100 bill Image taken from: http://www.scientific-web.com/en/Physics/Biographies/ErnestRutherford.html

12. Ernest Rutherford (1871 – 1937) • The repulsive force between the positively charged nucleus and positive alpha particles caused the deflections.

13. Robert Millikan(1909) • In the early 1910s, Robert Millikan used the oil-drop apparatus shown below to determine the charge of an electron.

14. Niels Bohr (1885 – 1962) • In 1913, proposed the Bohr Model, which suggests that electrons travel around the nucleus of an atom in orbits or definite paths. Additionally, the electrons can jump from a path in one level to a path in another level (depending on their energy) • Won a Nobel Prize • Worked with Ernest Rutherford Image taken from: commons.wikimedia.org/wiki/File:Niels_Bohr.jpg

15. Erwin Schrodinger (1887-1961) Image taken from: nobelprize.org/.../1933/schrodinger-bio.html • In 1926, he further explained the nature of electrons in an atom by stating that the exact location of an electron cannot be stated; therefore, it is more accurate to view the electrons in regions called electron clouds; electron clouds (Quantum Mechanical Model) • are places where the electrons are likely to be found • Did extensive work on the Wave formula  Schrodinger equation • Won a Nobel Prize

16. James Chadwick (1891 – 1974) • Realized that the atomic mass of most elements was double the number of protons  discovery of the neutron in 1932 • Worked on the Manhattan Project • Worked with Ernest Rutherford • Won a Nobel Prize Image taken from: www.wired.com/.../news/2009/02/dayintech_0227

17. Goldstein • Proton

19. - - + - - - - Progression of the Atomic Model The structure of an atom, according to: Democritus & John Dalton James Chadwick Neils Bohr Ernest Rutherford Erwin Schrodinger J.J. Thomson

20. Scanning Tunneling Microscope (STM) • electron microscope that shows three-dimensional images of a sample • Allows individual atoms to be seen • http://www.nobelprize.org/educational/physics/microscopes/scanning/

21. Atoms are mostly ____. A.positive B.negative C.solid spheres D.empty space

22. What are the two fundamental subatomic particles found in the nucleus? A.proton and electron B.proton and neutron C.neutron and electron D.neutron and positron

23. Periodic Tables tells us a lot!

24. Atoms vs Ions • Atoms have no charge • Equal protons and electrons • Ions have a charge • Electrons vary

25. Protons vs Electrons • Protons • Identity of the atom/ion • Each element always has the same number • Electrons • Behavior of the atom/ion • When more or less electrons are present, the atom becomes a charged ion

26. ISOTOPES • Same # of protons, but different mass # (and different # of neutrons) • Same chemical behavior • More neutrons, then greater mass • Relative abundance is usually constant • Same percentage found per sample

27. ISOTOPES • Atomic # (Z) = # of protons • Atomic Mass (A) = Protons + Neutrons • the weighted average mass of the isotopes • Mass # - Atomic # = # of neutrons • Atomic Mass Unit (AMU) : • 1/12th mass of Carbon-12 atom

28. Atomic Mass vs Mass Number • Atomic Mass • # of Protons • Weighted average (this is why it has a decimal) • Mass Number • # of Protons + # of Neutrons • Whole number (cannot have ½ a proton or electron)

29. ISOTOPES

30. ISOTOPES • Average Atomic Mass • [(mass #) x (abundance)] + [(mass #) x (abundance)] + [(mass #) x (abundance)] Abundance = use decimal not percentage

31. A • B • C • D An unknown element has 19 protons, 19 electrons, and 3 isotopes with 20, 21 and 22 neutrons. What is the element’s atomic number? A.38 B.40 C.19 D.unable to determine

32. A • B • C • D Elements with the same number of protons and differing numbers of neutrons are known as what? A.isotopes B.radioactive C.abundant D.ions