Foundations of Modern Atomic Theory: Unveiling the Secrets of Matter

1. CHAPTER 3Atoms: The Building Blocks of Matter CHEMISTRY

2. Foundations of Atomic Theory • History • Greek • Democritus – “atom” – could not be divided anymore • Aristotle and Plato - argued • 1600-1700s • Natural Philosophers • Experimentation – balances – quantitative measurements • Atom • Comes from Greek • “a” – not • “tomos” – cutting • indivisible

3. Foundations of Atomic Theory • Chemical Reaction • Transformation of substances into one or more new substances • Chemical change • Law of Conservation of Mass • Mass is neither created nor destroyed in ordinary chemical reactions • http://www.youtube.com/watch?v=dExpJAECSL8 • Law of Definite Proportions • A chemical compound contains the same elements in exactly the same proportions by mass regardless of size of sample • Ex – H2O, CO2

4. Foundations of Atomic Theory • Law of Multiple Proportions • If two or more compounds are composed of the same 2 elements, the masses can be expressed as ratios of small whole numbers

5. Dalton’s Atomic Theory • John Dalton • English School Teacher • 1803

6. Dalton’s Atomic Theory • 5 Points in his theory • All matter is composed of extremely small particles called atoms • Atoms of a given element are identical in size, mass, and other properties • Atoms cannot be subdivided, created, or destroyed • Atoms of different elements combine in simple whole number ratios to form compounds • In chemical reactions, atoms are combined, separated, or rearranged

7. Dalton’s Atomic Theory

8. Modern Atomic Theory • There have been some changes since Dalton’s Theory • Important concepts of modern theory • Atoms of one element can differ from each other - ISOTOPES • An atom is made of smaller parts

9. Structure of the Atom • Atom – smallest particle of an element that can exist alone • Two regions of an atom • Nucleus • Center of atom • Protons and neutrons • Electron “cloud” • Area surrounding nucleus containing electrons

10. Discovery of the electron • Symbol  e- • Cathode ray tubes (CRT) • Vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to form images in the form of light emitted from the fluorescent screen. • Used in TV, computer monitors

11. Discovery of the electron • Charge and mass of the electron • JJ Thomson – 1897 • Discovered the electron • 1907 Nobel Prize in Physics • http://videos.howstuffworks.com/hsw/6298-atomic-structure-electrons-video.htm • Did experiments with CRT – • Found that the charge to mass ration was always the same

12. Discovery of the atomic nucleus • Ernest Rutherford – 1908 • Gold Foil Experiment

13. Composition of the nucleus • Protons • Positive charge http://videos.howstuffworks.com/hsw/5806-atomic-structure-the-nucleus-video.htm • Neutrons • Neutral charge http://videos.howstuffworks.com/hsw/5807-atomic-structure-neutrons-video.htm

14. Forces in Nucleus • Nuclear forces • Forces that hold nuclear particles together • Binds protons and neutrons into the atomic nucleus

15. Sizes of Atoms • Based on distance electrons travel away from the nucleus • http://videos.howstuffworks.com/hsw/5788-size-of-atoms-matter-video.htm

16. Summary

17. Counting Atoms • Atomic Number • Symbol  Z • Number of protons in nucleus • The number of protons determines identity of the element!!

18. Counting Atoms • Isotopes • Atoms of the same element with varying number of neutrons • Nuclide – general term for any isotope of any element • Mass Number – total number of protons + neutrons

19. Counting Atoms • The isotope of hydrogen • Protium – one proton only; 1e- • Deuterium – one proton, one neutron, one electron • Tritium – one proton, two neutrons, one electron; radioactive • http://www.citycollegiate.com/isotopesofhydrogen.htm

20. Counting Atoms • Designating Isotopes • Hyphen notation • Name-mass # • Uranium-235 – How many p, n, e-? • Ex – Neon with 12 neutrons? • Nuclear Symbol Notation • MNANElement symbol • 31H • 23592U How many p,n,e- in chlorine-37?

21. Relative Atomic Mass • Relative scale • Standard needed to be set • Carbon-12 • All others compared to Carbon-12 • Atomic mass unit • amu • The mass of an individual atom • Honors: Approximate mass of a proton or a neutron

22. Average Atomic Mass • Weighted average of the atomic masses for all known isotopes • Calculating average atomic mass:

23. Relating mass to the number of atoms • “Particle” – a generic term • Mole – SI unit for amount of substance, counting unit • Symbol – mol • Avogadro’s number • 6.02 x 1023 – number of particles in 1mol of substance • Molar mass • Mass of 1mol of substance – on P.T.

24. Conversions • Gram  Mole Mole  Gram • Mole  Particle Particle  Mole • Gram  Particle Particle  Gram Facts (Conversion Factors): #g PT = 1 mol 6.02 x 1023 particles = 1 mol

25. Conversions • Gram  Mole; Mole  Gram

26. Conversions • Mole  Particle; Particle  Mole

27. Conversions • Gram  Particle; Particle  Gram