2.  Greek philosophers (300 BC) proposed matter was made of 4 elements: earth, air, fire, water.  Democritus coined the word “atom” meaning “cannot be broken.”  Atom seen as a solid sphere

3.  John Dalton (1766-1844) 1. All matter is made of atoms 2. Atoms are indestructible and can’t be divided 3. All atoms of one element are exactly alike, but different from atoms of other elements. 4. Atoms of diff elements combine in simple, whole-number ratios to make compounds 5. In reactions, atoms are combined, separated, or rearranged.

4.  1800s- scientists still thought atom was a tiny solid ball.  THEN…JJ Thomson (1897) discovers the electron (e-)

5.  Vacuum tube (no air inside) w/ electrode on each end, attached to a terminal.  He send electricity through the tube and saw  A bright ray travelling from the negative end (cathode) to the positive end (anode). “cathode rays”  Cathode ray bends toward a + end of a magnet.  “ “ bends away from a - end of a magnet.

7.  Cathode ray tubes pass electricity through a gas that is contained at a very low pressure. TelevisionComputer Monitor

8.  Conclusion: 1. The cathode ray was actually ____ charged particles. 2. The atom could not be ________ as scientists had thought, but must contain charged particles. 1909-scientists now believe the atom is like chocolate chip cookie dough

9.  In 1910 Thomson discovered that neon atoms have different masses.  Conclusion: there must be another particle that has no charge, called a neutron.  (In 1932, James Chadwick confirms existence of the neutron)

10. 1911-Rutherford’s Gold Foil Experiment Shot “alpha Particles” (helium nuclei) at gold foil. Hypothesis: they would pass through unaffected.

11. Expected results Actual results

12. a) The nucleus is small b) The nucleus is dense c) The nucleus is positively charged d) Most of the atom is empty space  Most of the particles passed right through  A few particles were deflected  VERY FEW were greatly deflected “Like howitzer shells bouncing off of tissue paper!” Conclusions:

13.  In 1920, Bohr proposes that electrons around the nucleus exist at only distinct distances from the nucleus  This is known as the Bohr model

14. ParticleCharge Mass (g) LocationElectron (e - ) (e - ) 9.11 x 10 -28 9.11 x 10 -28 Electron cloud Proton (p + ) +1 1.67 x 10 -24 1.67 x 10 -24Nucleus Neutron (n o ) (n o )0 1.67 x 10 -24 1.67 x 10 -24Nucleus

16.  The + charge on a proton is equal to the - charge on an electron.  Atoms are neutral (have no overall charge)  Therefore, the # of protons = # electrons in an atom.

17. Slide 2.2  determines the identity of the atom.  tells us the # of protons in the atom.  also tells us the # of electrons (b/c an atom is neutral in charge.)  Ex: atomic number of carbon, C = 6  Question: how many protons? How many electrons? How many neutrons ?...

18. Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element.Element # of protons Atomic # (Z) Carbon66 Phosphorus1515 Gold7979

19. Mass number is the number of protons and neutrons in the nucleus of an isotope: Mass # = p + + n 0Nuclide p+p+p+p+ n0n0n0n0 e-e-e-e- Mass # Oxygen - 10 -3342 - 31 - 3115 8 8 18 Arsenic 7533 75 Phosphorus 15 31 16

20.  (Def) Atoms of the same element w/different #s of neutrons.  The number of neutrons can vary from atom to atom in an element.  In order to know how many neutrons in an atom you must be told.  The mass number tells you how much mass the atom has.  Since p + and n 0 are the heavy parts,  mass # = # of p + ’s + n 0 ’s.

21. B 5 11 Atomic # Mass # Symbol for element

22.  The atom in the prior slide can be called “boron-11” Name of element Mass #

23.  How many protons?  How many electrons?  How many neutrons?  LET’S PRACTICE!  Whiteboard  Marker  Paper towel

24. Practice Problem #1 n If an element has an atomic number of 34 and a mass number of 78, what is the: a) number of protons b) number of neutrons c) number of electrons d) complete symbol

25. Practice Problem #2 n If an element has 78 electrons and 117 neutrons what is the a) Atomic number b) Mass number c) number of protons d) complete symbol

26.  Atoms are weighed in a.m.u.  1 a.m.u. is based on the mass of a Carbon-12 atom.  it has 6 p+ and 6 n 0,  1 a.m.u = 1/12 the mass of a carbon-12 atom.

27.  (definition) Weighted average of all the isotopes of an element. See p 68 of text. calculating atomic mass  Located below element symbol on periodic table.

28. Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. IsotopeProtonsElectronsNeutronsNucleus Hydrogen–1 (protium) (protium)110 Hydrogen-2(deuterium)111 Hydrogen-3(tritium)112

29. Elements occur in nature as mixtures of isotopes. Isotopes are atoms of the same element that differ in the number of neutrons.

30.  Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.  If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu)

31. IsotopeSymbol Composition of the nucleus % in nature Carbon-12 12 C 6 protons 6 neutrons 98.89% Carbon-13 13 C 6 protons 7 neutrons 1.11% Carbon-14 14 C 6 protons 8 neutrons <0.01% Atomic mass is the average of all the naturally occurring isotopes of that element. Carbon = 12.011

32.  Copper has the following isotopes ISOTOPE MASS # % ABUNDANCE  Copper-63 63 69.15  Copper-65 65 30.85  Calculate the atomic mass (average mass)

33. Finding Atomic Mass on Periodic Table

36. Ch 5 – Chem IH Ch2.2 & 7 – Chem I

37. Energy can travel in waves. There are high energy and low energy waves. The ones we can see are called “the visible spectrum.” ROY G BIV Red is the low energy end: violet is the high energy end.

38.  1. Wavelength: distance between crests of a wave. Ex: radio waves = 10 2 m

39.  2. Frequency: number of wave cycles to pass a point per unit time.

40. Energy of Electrons  Why electrons don’t crash into the nucleus: they have enough energy to keep them away.  Why e-s (usually) don’t fly off of atoms: they have enough attraction to the nucleus to keep them in “orbit.” (Kind of like planets in orbit around the sun.)

41. (Don’t write this!) DISCUSS WITH YOUR NEIGHBOR:  You are an electron. If you have a lot of energy, will you stay close to the nucleus or will you move further from it? Answer: you may still stay in “orbit” but you will be able to move further away from the nucleus.

42.  Neils Bohr studied w/Rutherford  His model is also called the planetary model  He discovered that e-s could only exist at certain distances from the nucleus. (Energy Levels)

43.  "The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth." Neils Bohr

44.  See p 75 of text: electron energy levels are like rungs of a ladder.  Ladder  To climb to a higher level, you can’t put your foot at any level,  you must place it on a rung  Electron energy levels  e-s must move to higher or lower e.l.’s in specific intervals

45.  Interactive Bohr Model Interactive Bohr Model

46.  Atoms are arranged in energy levels (e.l.’s), at different distances from nucleus  Close to nucleus = low energy  Far from nucleus = high energy  e-s in highest occupied level are “valence e-s”  Only so many e-’s can fit in energy levels  e-s fill lower e.l.’s before being located in higher e.l.’s* (* There are exceptions we will learn later!)

47.  Only so many e-’s can fit in energy levels Energy Level# of electrons 1 st 2 2 nd 8 3 rd 18* 4 th 32*

48.  VALENCE ELECTRONS DETERMINE HOW ELEMENTS BEHAVE!!!

49. Let’s practice drawing some atoms/ions In your teams, pick up enough of the following for your team: 1 white board per person 1 marker per person 1 paper towel per team (Please save a tree & share!)

50.  Electrons aren’t in perfect orbits.  Energy levels are regions of space in which an e- is likely to be found most of the time.  The area in which they move is like a cloud, an area of space surrounding the nucleus.

51.  Show # of protons and neutrons in the nucleus  Draw e.l.’s and show each electron in the proper e.l.  Ex: Bohr Model of BORON-11Bohr Model of BORON-11

52.  Hydrogen-2 (Practice together)  Helium-4  Lithium-6  Beryllium-8  Carbon-12  Magnesium-24

53. Have 2 parts 1. Chemical symbol of element 2. Valence e-s, represented by dots  Are placed in one of four locations  Above  Below  Right  left  Are not paired unless there is 1 e- in each location.  Ex: OxygenOxygen

54. TEACHER DEMONSTRATION  Hydrogen  Helium  Lithium STUDENT PRACTICE  Beryllium  Boron  Carbon

55.  Bohr Models  Lewis dot diagrams