Chapter 2 Atoms – The Building Blocks of Matter

1. Chapter 2Atoms – The Building Blocks of Matter The Atomic Theory

2. Atomic Theory • Law of Conservation of Mass • Law of Definite Proportions • Law of Multiple Proportions

3. Conservations of Mass In chemical changes, no matter how big the bang, mass is neither gained or lost. Law of conservation of matter: Matter cannot be made or destroyed by ordinary chemical means.

4. Law of Definite Proportions A particular chemical compound is always composed of the same combination of atoms - copper(II) carbonate CuCO3*Cu(OH)2 http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH02/FG02_01.JPG

5. Law of Multiple Proportions • If two elements form more than one compound between them, then the ratios of the weights of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH02/FG02_02.JPG

6. Democritus 400 BC By convention there is color,By convention sweetness,By convention bitterness,But in reality there are atoms and space.   -Democritus (c. 400 BCE)

7. Democritus 400 BC Atoms - • Invisible • Indivisible • Solid • Eternal • Surrounded by an empty space • Have an infinite number of shapes http://www.brl.ntt.co.jp/group/butsuden-g/img/redball.gif

9. Democritus 400 BC Atoms - http://www.brl.ntt.co.jp/group/butsuden-g/img/redball.gif

10. 1750, chemistry was seeking to gain its independence from the four disciplines which had engendered it: industry, the natural sciences, alchemy and medicine.

11. Conservation of Mass Antoine-Laurent de Lavoisier 1743 - 1794

12. Everything can be measured, hence calculated and, just as in a balance sheet, the total of the outflow must always equal that of the inflow.. • The entire art of carrying out experiments in chemistry is based on this principle.

13. Conservations of Mass In chemical changes, no matter how big the bang, mass is neither gained or lost. Law of conservation of matter: Matter cannot be made or destroyed by ordinary chemical means.

14. Law of Definite Proportions A particular chemical compound is always composed of the same combination of atoms - copper(II) carbonate CuCO3*Cu(OH)2 http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH02/FG02_01.JPG

15. Law of Multiple Proportions • If two elements form more than one compound between them, then the ratios of the weights of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH02/FG02_02.JPG

16. John Dalton 1766-1844 http://www.unit5.org/christjs/John_Dalton.htm

17. Dalton's atom - 1803

18. Dalton’s Theory • Each element is made up of tiny particles called atoms. Atoms can neither be created nor destroyed. • All atoms of the same element are identical in mass, size, and other properties. • Atoms of one element differ in mass and other properties from atoms of other elements. • Atoms cannot be created, destroyed, subdivided, or changed into atoms of another element. • Atoms of different elements combine in fixed, simple, whole-number ratios to form compounds

19. JJ Thomson 1856-1940 Excuse me... how can you discover a particle so small that nobody has ever seen one? http://www.aip.org/history/electron/jjsound.htm

20. Thomson & the Electron JJ Thomson used the cathode ray tube which had rays going through it. He found that when he introduced a magnet to the tube, the ray was deflected. This proved that the atoms traveling though it must be charged, He found out later that this charge was negative. This is the first atomic subparticle http://www.broadeducation.com/htmlDemos/AbsorbChem/HistoryAtom/page.htmt

22. Thomson 1. Cathode rays are beams of negatively-charged particles called electrons.  2. All atoms contain electrons.  3. Atoms must contain positive charge.

23. Thomson's “Plum Pudding Model" In 1904 he suggested a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. http://www.broadeducation.com/htmlDemos/AbsorbChem/HistoryAtom/page.htmt

24. Thomson's “Plum Pudding Model" http://molaire1.club.fr/e_histoire.html

25. Ernest Rutherford 1871-1937 • "All science is either physics or stamp collecting." http://www.pbs.org/wgbh/aso/databank/entries/bpruth.html

26. Rutherford’s Gold Foil Results

27. What He thought would happen

28. What Actually Happened

30. Rutherford’s Atom • He discovered the atomic nucleus and developed a model of the atom that was similar to the solar system. Like planets, electrons orbited a central, sun-like nucleus. http://www.broadeducation.com/htmlDemos/AbsorbChem/HistoryAtom/page.htmt

31. Rutherford’s Atom 1. Most of the mass of an atom must be located in a small volume at the center of the atom (the nucleus). 2. The nucleus is made of positively charged particles called protons. 3. The electrons move in a large volume which is mostly empty space.

32. Problems with Rutherford’s Atom • According to "classical" theory the electrons should lose energy by radiating electromagnetic radiation, as they are accelerated electric charges. • They should spiral into the nucleus.

33. Problems with Rutherford’s Atom The orbiting electron in the Bohr atom would eventually spiral into the nucleus of the atom.

34. Neils Bohr1885 - 1962

35. Bohr’s Idea It had been known for some time that the light given out when atoms were heated always had specific amounts of energy, but no one had been able to explain this.

36. Bohr’s Idea Bohr suggested that the electrons must be orbiting the nucleus in certain fixed energy levels (or shells). The energy must be given out when 'excited' electrons fall from a high energy level to a low one.

37. Bohr’ Theory • Quantum Mechanics. It said that energy could only change in little jumps. These are called quanta http://www.colorado.edu/physics/2000/quantumzone/bohr.html

38. Bohr’s Atom

39. When the electron is in an allowed orbit, it does not radiate energy. It is stable. Stable orbits are called stationary states • Atom emits energy (gives off a photon) only when moving from high energy state to another. • Atom absorbs energy (captures a photon) when moving from low to high energy levels.

40. Bohr’ Theory • Quantum Mechanics. It said that energy could only change in little jumps. These are called quanta http://www.colorado.edu/physics/2000/quantumzone/bohr.html

41. Bohr’s Atom http://www.colorado.edu/physics/2000/quantumzone/bohr.html

42. James Chadwick

43. Chadwick • In 1932, Chadwick proved the existence of neutrons - elementary particles devoid of any electrical charge. • Located in the nucleus (Rutherford also put out the idea that there could be a particle with mass but no charge)

44. Chadwick • He studied atomic disintegration, he kept seeing that the atomic number (number of protons in the nucleus, equal to the positive charge of the atom) was less than the atomic mass.

45. Chadwick • For example, a helium atom has an atomic mass of 4, but an atomic number (or positive charge) of 2. Since electrons have almost no mass, it seemed that something besides the protons in the nucleus were adding to the mass.

46. Chadwicks Atom

47. The Modern Atom 1. Most of the atom's volume is occupied by space. 2. The number and arrangement of electrons in an atom determine its chemical properties.

48. The Modern Atom 3. The identity of an element is determined by the number of protons in the nucleus. 4. Different isotopes of elements exist and differ only in the number of neutrons and hence the mass of the atom.

49. Modern Atom • Electrons • Protons • Neutrons

50. Electrons •  Electrons are tiny particles which behave like clouds • Electrons carry a negative electric charge. • Electrons are responsible for the chemistry of the atom.