1 / 17

Evolution of Atomic Theory: From Democritus to Modern Science

Explore the development of atomic theory from Democritus to modern times, including Dalton's theory, Rutherford's experiments, and the structure of atoms.

licht
Download Presentation

Evolution of Atomic Theory: From Democritus to Modern Science

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. Chapter 3A ATOMS: The Building Blocks of Matter EQ: Describe how atomic theory developed to give us our modern view of the atom. Chapter #3 • Atoms: The Building Blocks of Matter

  2. 3-1 Early Atomic Theory • Atoms – smallest particle of matter. • Democritus (400 B.C) stated world was made of atoms. (atomos = “indivisible”). • Antoine Lavoisier (1800’s) discovered mass didn’t change after chemical rxn. • Proposed “matter can be changed, but it cannot be created or destroyed “ (Law of Conservation of Mass).

  3. Dalton’s Atomic Theory • All matter composed of atoms. • Atoms of same element identical in size, mass, properties; atoms of diff elements diff. in size, mass, properties. • Atoms can’t be subdivided, created, destroyed. • Atoms of different elements combine in whole-number ratios to form chemical compounds. • In chemical reactions, atoms are combined, separated, or rearranged.

  4. Modern Atomic Theory • All matter is composed of atoms. • Atoms of any one element differ in properties from atoms of another element. • Element’s average mass unique to element. • Atoms cannot be subdivided, created, or destroyed in ordinary chemical rxns. • Changes CAN occur in nuclear rxns!

  5. Section 3-2 • Atom- smallest particle of element that retains chemical properties of element. • Nucleus- positively charged, dense central portion of the atom; contains nearly all mass (~ 99.7%).

  6. Subatomic Particles

  7. The Atomic Scale • Most of the mass of the atom is in the nucleus (protons and neutrons) • Electrons are found outside of the nucleus (the electron cloud). • Most volume of atom=empty space.

  8. Famous Scientist

  9. Discovery of the Electron • J.J. Thomson (1897) used a cathode ray tube to deduce the presence of a negatively charged particle. • Discovered the – electron particle.

  10. (1906)Thomson awarded the Nobel Prize in chemistry for discovery of the electron. • The atom could be broken down into smaller particles.

  11. Thomson’s Atomic Model • Thomson believed electrons were like plums in a + charged “pudding”. • He called it the “plum pudding” model.

  12. Rutherford’s Gold Foil Experiment • Alpha particles are helium nuclei. • Particles fired at a thin sheet of gold foil. • Particle hits on screen (film) are detected.

  13. Rutherford’s Findings • Most particles passed right through screen. • Few particles deflected. • VERY FEW were greatly deflected. • Conclusions: • The nucleus is small. • The nucleus is dense. • The nucleus is + charged.

  14. Section 3-3 • Atomic number: number of protons in the nucleus of atom. • # p(+) = # e(-) 6 C Carbon 12.011

  15. Atomic Mass • number of protons & neutrons in the nucleus. • Atomic Mass=protons + neutrons • Atomic Mass C = 12.011 • Mass number = rounded atomic mass • Mass Number C = 12

  16. Nuclear Symbols 235 92 Mass number (p+ + n) Atomic Mass (p+ + n) Element symbol Atomic number (# of p+) U 235 92

  17. Hyphen Notation Sodium-23 (23 is the atomic mass) Sooo… 23- 11 (atomic #) = 12 for the # of neutrons. Atomic number of 11 is the # of protons (11) and electrons(11).

More Related