1 / 20

How do we know about atoms?

How do we know about atoms? . Atomic Theory. Democritus (460 BC- 370 BC). His mentor Leucippus Everything is composed of “atoms” Atoms are physically indivisible Between atoms is empty space Atoms are always in motion

vilina
Download Presentation

How do we know about atoms?

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. How do we know about atoms? Atomic Theory

  2. Democritus (460 BC- 370 BC) • His mentor Leucippus • Everything is composed of “atoms” • Atoms are physically indivisible • Between atoms is empty space • Atoms are always in motion • Infinite number of atoms and kinds of atoms which differ in shape and size

  3. John Dalton (1766-1844) • Postulated the following: • that all matter was made of some type of particle- called atoms which could not be broken up or destroyed • Atoms could combine with different atoms to form compounds • All atoms of the same element are the same size (mass) and have the same properties • Atoms can be rearranged during a chemical reaction to form new substances

  4. Discovery of Electron • JJ Thomson in 1897 • Cathode Ray Tubes- A cathode ray forms when high voltage is applied to a partially evacuated tube. The ray passes through a hole in the negative end of the tube and hits the coated end of the tube to produce a glow

  5. Plum Pudding Model • Know that there are electrons (negative) • Must be a positive part as well in order to be neutral

  6. Discovery of the Nucleus • Ernest Rutherford designed an experiment to test the Plum Pudding Model. • Expected all particles to go straight through the foil

  7. They didn’t all go straight through? • Why?

  8. New Model = Nucleus

  9. Nucleus • Contains the mass of the atom. • 20 years later, James Chadwick discovered the neutron because the entire mass of the nucleus could not be accounted for by just protons.

  10. Re-examining Dalton’s Atomic Theory • Which postulates had to be modified after JJ Thomson and Ernest Rutherford’s experiments?

  11. All atoms are the same size- isotopes • Atoms can’t be changed- nuclear reactions • All mater is made of atoms – a proton is still matter

  12. Atomic Symbol -

  13. Isotopes • All atoms of an element are identical in atomic number, but not in atomic mass. • Isotopes = different number of neutrons. • Electrons determine chemical properties of an element. • Can determine neutrons from atomic mass and atomic number

  14. Using the info on the PT • How many protons, neutrons and electrons does an atom of iron have?

  15. Atomic Masses on the PT • How come they have decimals? • Does a single neutron or proton weight exactly 1 amu?

  16. Atomic Mass Unit (amu) • The mass of an atom is measured relative to the mass of an atomic standard. • The standard = carbon-12 atom. • 1 carbon-12 atom has exactly 12 amu

  17. Atomic Mass • The mass represented on the periodic table is the average of all of the naturally occurring isotopes weighted accordingly to their abundances. • PROBLEMS: find the abundances of isotopes based on the atomic mass. OR predict the atomic mass based on the abundances of certain isotopes

  18. Finding Atomic Mass • Magnesium has 3 naturally occurring isotopes, 24Mg (23.9850 amu, abundance 78.99%), 25Mg (24.9858 amu abundance 10.00%), and 26Mg (25.9826 amu, abundance 11.01%). Calculate the atomic mass of magnesium.

  19. Sample Problem • Boron has 2 naturally occurring isotopes. Find the percent abundance of Boron-10 and Boron-11 given the atomic mass = 10.81 amu. The isotopic mass of Boron-10 = 10.0129 amu, and the isotopic mass of Boron-11 = 11.093 amu.

  20. Homework: • Pg 69: # 1 (a,b,c), 2, 9, 20 (a,b,c) 21, 22, 23 (a,b), 29, 32, 91 • Read about mass spectroscopy on page 48, and summarize what it is

More Related