1 / 20

Composition of an Atom

Composition of an Atom. Models of the Atom: A Historical Perspective. Atomic Theory Timeline. 400 B.C. Democritus. Democritus. In 400 B.C. Democritus believed all existence consisted of two things: atoms (coined the term atom from the Greek word ‘ atomos ’ meaning indivisible)

jesus
Download Presentation

Composition of an Atom

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Composition of an Atom Models of the Atom: A Historical Perspective

  2. Atomic Theory Timeline 400 B.C. Democritus

  3. Democritus • In 400 B.C. Democritus believed all existence consisted of two things: • atoms (coined the term atom from the Greek word ‘atomos’ meaning indivisible) • the void (space) • Democritus’ theory: • atoms are particles in space (the void) • atoms always in motion; make life predictable • matter could not be divided indefinitely; atoms are indivisible • all things we see differ because of the shape, size, and arrangement of atoms

  4. Atomic Theory Timeline 400 B.C. 350 B.C Democritus Aristotle

  5. Aristotle • In 350 B.C. Aristotle and his followers dismissed the idea of atoms • Instead modified an earlier theory that matter was made up of four ‘elements’: • earth • fire • water • air • Even though Aristotle was wrong his theory persisted for 2000 years!

  6. Atomic Theory Timeline 1743-1794 400 B.C. 350 B.C 0 Lavoisier Democritus Aristotle

  7. Lavoisier • During his lifetime, 1743-1794, Antoine Lavoisier established the Law of Conservation of Matter • Law= in a chemical reaction, the mass of the reactants is equal to the mass of the products • Theory stated that mass is concrete and measurable, rather than ‘magical’

  8. Atomic Theory Timeline 1743-1794 400 B.C. 350 B.C 1800 0 Dalton Lavoisier Democritus Aristotle

  9. Dalton • In 1800 John Dalton was examining gases dissolved in water and decided that matter was made of individual particles with spaces between them • Devised a chemical atomic theory: • all matter is made of atoms • atoms of an element are identical • each element has different atoms • atoms of different elements combine in constant ratios to form compounds • atoms are rearranged in reactions

  10. Atomic Theory Timeline 1743-1794 400 B.C. 350 B.C 1800 0 1900 Dalton Lavoisier Thomson Democritus Aristotle

  11. Thomson • In 1897, looking at charged particles, J.J Thomson found particles that had a charge that did not change regardless of the metal they came from… • He called these charged particles electrons (negatively charged particles) • Later he proposed a model for the composition of the atom called the ‘raisin bun’ or ‘plum pudding model’ although he was proved to be incorrect

  12. Adding Electrons to the Model • Materials, when rubbed, can develop a charge difference. This electricity is called ‘cathode rays’ when passed through an evacuated tube • These rays have small mass and are negative • Thomson noted that these negative subatomic particles were a fundamental part of all atoms • 1) Dalton’s ‘Billiard Ball’ model (1800-1900): • atoms are solid and indivisible

  13. 2) Thomson’s ‘Plum Pudding’ Model (1900): • negative electrons in a positive framework 3) The Rutherford Model (around 1910): • atoms are mostly empty space • negative electrons orbit a positive nucleus

  14. Atomic Theory Timeline 1743-1794 400 B.C. 350 B.C 1800 0 1900 Dalton Lavoisier Democritus Aristotle Thomson 1903 Rutherford

  15. Rutherford • Used radiation to unlock clues to the atom; alpha particle (α) -positive charge and beta particle(β) -negative charge • Ernest Rutherford short alpha (α) particles at gold foil • Most particles passed through; therefore, atoms are mostly empty • Some positive alpha deflected or bounced back! • Thus, a ‘nucleus’ is positive and holds most of an atom’s mass

  16. Atomic Theory Timeline 1743-1794 400 B.C. 350 B.C 1800 0 1900 Dalton Lavoisier Democritus Aristotle Thomson 1903 1907 Millikan Rutherford

  17. Millikan • In 1907 Robert Millikan found that all electrons are identical • Millikan was able to find the charge of a single electron

  18. Atomic Theory Timeline 1743-1794 400 B.C. 350 B.C 1800 0 1900 Dalton Lavoisier Democritus Aristotle Thomson 1907 1903 1913 Bohr Rutherford Millikan

  19. Bohr • Around 1913 Niels Bohr discovered that electrons orbit the nucleus in ‘shells’ • Electrons can be bumped up to a higher sell if hit by an electron or a photon of light • It is when electrons fall back down energy level(s) that they release a photon

  20. There are two types of spectra : • continuous spectra • line spectra • These jumps down from shell to shell account for the line spectra seen in gas discharge tubes (through spectroscopes)

More Related