2. THE ATOM is defined as… The smallest particle of an element that still has properties of that element. But where did this idea come from?

3. “If you break a piece of matter in half, and you break it again… how many breaks will you have to make, until you can break it no further?” DEMOCRITUS Around 460 B.C… Democritus thought it ended with a single particle…the smallest bit of matter. He called these bits of matter “atoms”. Like most things, it started with the Greeks….

4. People got busy…

5. 1. All matter is composed of atoms. 2. Atoms of a given element are identical in size, mass, and other properties. 3. Atoms of different elements have different number of protons 4. Atoms unite in simple, whole number ratios to form compounds 5. Atoms cannot be subdivided, created, destroyed. It is a SOLID, INDIVISIBLE SPHERE.

6. J. J. Thompson’s Contributions He wanted to test Dalton’s idea that the atom was a tiny solid ball aka solid, indivisible sphere Thomson worked around 1897, and was given credit for discovering the ELECTRON! His model of the atom is called the “plum pudding” model because he thought electrons existed in a ball of positive charge.

8. Rutherford’s Contribution… In order to investigate the struture within the atom, around 1911 – the Gold Foil Experiment was performed. This is the most important contribution you are responsible for knowing.

9. Rutherford in short… Wanted to test Dalton and Thomson models: Shot alpha particles which are positive through a sheet of gold foil. Most of the alpha particles pass through the gold foil. But a few were deflected back. This meant that there was something small and positive in the center of the gold atoms – hence the nucleus that contained positive charges. Because most of them went through – nucleus must be very small in comparison to the volume of the entire atom.

10. Rutherford’s Gold Foil Exp.

12. 2 major conclusions supported by evidence: 1. The atom is made up of mostly empty space. EVIDENCE: Most of the alpha particles passed through the gold foil and were detected on the screen. 2. The nucleus is small, dense, positively charged center. EVIDENCE: A miniscule percentage of the positive alpha particles were deflected back, meaning the there must be a positively charged mass inside the atom. I STOLE THIS FROM THE REGENTS EXAM. YOU SHOULD PROBABLY REMEMBER IT.

13. Neil Bohr Neil Bohr is responsible for attempting to explain how the electrons and the nucleus interacted. Thompson had discovered the electron as a negatively charged particle and Rutherford concluded that the nucleus was a positive center. Neil Bohr introduced what is called the “planetary model” of the atom: Electrons travel in specific, circular orbits around the positive nucleus. These orbits are a fixed distance away from the nucleus.

14. These circular orbits are known as energy levels. The energy levels are fixed but the electrons can jump from one to the next. When electrons are given energy… they can jump up to a higher energy level. When electrons release energy, they fall back down. The energy is released in the form of light..

16. Modern Model: Wave Mechanical As technology improved, Neil Bohr’s model of the atom didn’t hold up… Evidence suggested that electrons didn’t travel in specific energy levels… Scientists like Heisenberg, Planck, Schrodinger, Pauli modified the model.. And it is how we accept to this day..

17. Modern Model: Wave Mechanical Due to the interaction between the electron and the nucleus and the constant motion of the electron, they concluded that… The exact location of an electron is never known. All we can know is a general space in which the electron might be found. This general space is known as an ORBITAL

19. Wave Mechanical Model … The orbital is defined as the three- dimensional region of probability of finding an electron. Each orbital can only hold 2 electrons at a time. I STOLE THIS LINE FROM THE REGENTS EXAM too. YOU SHOULD PROBABLY REMEMBER IT.

21. The evolution of the atom…

22. MORAL OF THE STORY: The modern model of the atom is based on the work of MANY scientists over a long period of time. I STOLE THIS LINE FROM THE REGENTS EXAM. YOU SHOULD PROBABLY REMEMBER IT.

23. What particles are found in the atom and how are they important?

24. PROTONS : Protons have a mass of 1 AMU (atomic mass unit) and a charge of +1. The number of protons is called the ATOMIC NUMBER, and is used to identify an atom or element. Due to their location and charge, the number of protons is also known as the nuclear charge. (particles found in the nucleus)

25. Each element has a unique number of protons, which is used to identify the element The number of protons is known as the

26. Examples… What is the atomic number of…. What is the atomic number of…. F? F? Ca? Ca? Hg? Hg? Au? Au? Kr? Kr?

27. NEUTRONS: Neutrons also have a mass of 1 AMU, but have a charge of 0. They are neutral. The number of neutrons does not effect the charge or the identity of an atom. Atoms of the same element can have a different number of protons and neutrons and still keep their identity. They are called isotopes. More on that later… (particles found in the nucleus)

28. ELECTRONS: Electrons are NOT nucleons because they are found in the area outside of the nucleus. Electrons have a charge of -1 and they are found orbiting the nucleus in orbitals and energy levels. We say that the charge of an electron is equal but opposite to that of a proton. Electrons are 1/1836 th the mass of a proton, so we say that their mass is negligible because it is so small in comparison. However, of course it has mass because it is matter.

29. The Mass of the Atom Based upon the mass of the subatomic particles, we can tell that most of the mass is found in the nucleus. Therefore, we can assign every atom a “mass number” which is based upon how many protons and neutrons are in the nucleus. Mass Number = Protons + Neutrons Note: Mass number is NOT THE SAME as Atomic Mass. We’ll discuss this shortly.

30. The Nuclear Symbol: This element has … PROTONS NEUTRONS ELECTRONS 2 2 2 Given the nuclear symbol… we get the number of neutrons by doing the simple calculation: Mass Number – Atomic Number.

32. Examples… CBHgPbMgNOFCu Element Atomic Number Mass Number ProtonsNeutronsElectrons

33. Vs. 12 PROTONS NEUTRONS ELECTRONS PROTONS NEUTRONS ELECTRONS 686686 666666

34. Two atoms of the same element must have the same number of protons. However, they can have a different number of neutrons. These are called isotopes. Same Atomic Number Different Mass Number

35. Isotope examples… Hydrogen has three isotopes Hydrogen has three isotopes A. Protium: 99.985% of all Hydrogen is protium: 1 proton, 1 electron. A. Protium: 99.985% of all Hydrogen is protium: 1 proton, 1 electron. B. Deuterium: 0.015% of all Hydrogen, has 1 proton, 1 electron, 1 neutron. B. Deuterium: 0.015% of all Hydrogen, has 1 proton, 1 electron, 1 neutron. Tritium: Exists in very small amounts in nature and is RADIOACTIVE. Has 1 proton, 1 electron and 2 neutrons. Tritium: Exists in very small amounts in nature and is RADIOACTIVE. Has 1 proton, 1 electron and 2 neutrons.

36. On the periodic table, we can determine which is the most common isotope of any element. For this example… the most common isotope of Fe is Fe-56. We get this by rounding off the atomic mass to the nearest whole number.

37. Things to Know About Isotopes: 1. Same atomic number, different mass number. 2. Same number of protons, different number of neutrons. 3. Must be the same element

38. Which of the following are isotopes? 14 C 6 14 N 7 16 O 8 12 C 6 Same atomic number, different mass

39. In certain times, neutral atoms will either gain or lose 1 or more of their electrons These charged particles are called ions Positive ions are called CATIONS Negative ions are called ANIONS Ions

40. Ions… When an element gains an electron, it becomes a negative ion. This is because it is adding an extra negative charge. When an element loses an electron, it becomes a positive ion. This is because it is losing a negative charge that was balancing a proton.

41. Ions… Ions can be represented as part of the atomic symbol as well. Ions can be represented as part of the atomic symbol as well. 30 P 3- 15 The sign of the charge tells us if electrons were gained or lost. The quantity tells us how many electrons

42. Determine the protons, neutrons and electrons for the following atom: Protons = Neutrons = Electrons = 24 Mg 12 12 12 12

43. Determine the protons, neutrons and electrons for the following atom: Protons = Neutrons = Electrons = 137 Ba 56 56 81 56

44. Determine the protons, neutrons and electrons for the following atom: Protons = Neutrons = Electrons = 56 Fe 26 26 30 23 +3

45. Determine the protons, neutrons and electrons for the following atom: Protons = Neutrons = Electrons = 35 Cl 17 17 18 18

46. Determine the protons, neutrons and electrons for the following atom: Protons = Neutrons = Electrons = 27 Al 13 13 14 10 +3

48. This is what you do every single time you are asked to “calculate the atomic mass” They wouldn’t ask you to calculate it, They wouldn’t ask you to calculate it, if they wanted to you to read it off the periodic table. if they wanted to you to read it off the periodic table.

49. Where did the number 55.847 amu come from? Calculate the average of the mass numbers of all the isotopes…

50. Atomic Mass Calculations Atomic Mass is the weighted average of all the naturally occurring isotopes of a particular element Atomic Mass = Mass Number I STOLE THIS LINE FROM THE REGENTS EXAM too. YOU SHOULD PROBABLY REMEMBER IT.

51. How is this different from the mass number? The mass number is a literal count of protons and neutrons in an individual atom. It is always a whole number. However, because isotopes exist – atoms of the same element may have a different mass numbers. When coming up with the mass of an element, we have to take all of the different isotopes and the abundance into consideration. The atomic mass is almost always a decimal because it is a WEIGHTED average.

52. Steps to CALCULATE a Weighted Average Atomic Mass: 1. Change abundance percentages to decimals by moving decimal two to the left. 2. Multiply abundance by respective mass numbers 3. Add the products together. 4. Label “amu”

54. Example and How-To A sample of Carbon contains 78.00% Carbon-12 and 22.00% Carbon 14. What is the atomic mass of this sample? First, change percentages to decimals. Then multiply decimal by respective mass number. Then add them together. 78.00 %  0.7800 22.00%  0.2200 X 12 X 14 = 9.360 = 3.080 + 12.440 amu

55. Example 2: A sample of Sodium contains 80.0 % Na-23, 15.0 % Na-22 and 5.0% Na-24. What is the atomic mass of this sample? 0.800 x 23 = 18.4 0.150 x 22 = 3.30 0.050 x 24 = 1.2 + 22.9 amu

56. Example 3: A sample of Boron has two naturally occuring isotopes. B-10 has a mass of 10.0 amu and makes up 19.80% of all B atoms. B-11 has a mass of 11.0 amu and makes up 80.20% of B atoms. What is the average atomic mass of Boron? Answer: 10.802 amu

57. Key Idea: The atomic mass listed on the Periodic Table is always closest to the most abundant isotope. Just like your marking period average is always closest to your test average. Hydrogen has three isotopes with mass numbers of 1, 2, and 3 and has an average atomic mass of 1.00794 amu. This information indicates that: 1. equal numbers of each isotope are present 2. more isotopes have an atomic mass of 2 or 3 than of 1 3. more isotopes have an atomic mass of 1 than of 2 or 3 4. isotopes have only an atomic mass of 1

59. Think of an electron configuration as an address for the electrons in an atom. It is our best guess as to what the inside of an atom looks like. The scientists whose models deal with electron configuration are Bohr and all the gentlemen of the Wave Mechanical Model. When we come up with electron configurations or electron addresses – we use a little bit of both models to give us our best visualization.

60. Electron Shells: The shell configuration is found at the bottom of the box on the periodic table for each element. It gives a very rough estimatation of electron location. It is the principle that Neil Bohr is responsible for. The electron shells are called principle energy levels or PEL’s.

61. The electrons fill from the inside out as follows: 1 st PEL (closest to nucleus) holds 2 electrons 2 nd PEL holds 8 electrons 3 rd PEL holds 18 electrons 4 th PEL holds 32 electrons This continues all the way to the 7 th PEL, as electrons fill from the inside out. LOWEST ENERGY HIGHER ENERGY

62. Each P.E.L can only hold a certain number of electrons. Max # of Electrons = 2n 2 where “n” is 1  7

63. This allows to write the basic electron configuration for any element on the periodic table. This is also provided for you on the Periodic Table in your Reference Tables.

64. Write the basic electron configuration for the following elements: no cheating! O N NaC ClNe P Al 2-6 2-8-1 2-8-7 2-8-5 2-5 2- 4 2-8 2-8-3 8 11 17 15 7 6 10 13 Atomic Number

65. The electrons found in the outermost principle energy level are called the valence electrons. The valence electrons are the electrons that participate in bonding with other atoms.

66. Nitrogen has 2 energy levels. It has 5 electrons in the 2 nd p.e.l. Therefore, 5 valence electrons. Lithium has 2 energy levels. It has 1 electron in the 2 nd p.e.l. Therefore, 1 valence electron.

68. PEL can be broken down into more specific “homes” for the electrons. Each PEL is made up of sublevels 1 st PEL: “S” sublevel: 2 nd PEL: “S” and “P” sublevels 3 rd PEL: “S”, “P”, “D” sublevels 4 th PEL: “S”, “P”, “D”, “F” sublevels

69. PEL can be broken down into more specific “homes” for the electrons. Each sublevel can be broken down into orbitals... Recall that an orbital is a 3D region of finding electrons… only 2 e- can occupy an orbital. S = 1 orbital P = 3 orbitals D = 5 orbitals F = 7 orbitals

71. If each orbital contains 2 electrons, they must have opposite spins. We use “up” and “down” arrows to represent different spins. Or, we use +½ and – ½. This is called “Hunds Rule”

72. 2 8 18 32

73. We can write expanded e- configurations using all of this information. RULES: 1. # of electrons in a neutral atoms = protons 2. Each orbital can have no more than 2 electrons, with opposite spins 3. Fill in e- starting with the lowest energy level first. Fill in 1s before 2s. 2s before 2p. Follow the “diagonal rule” 4. Orbitals of equal energy level are occupied by 1 electron, before any orbital is occupied by 2 electrons.

74. Basic Example: H: 1 electron 1s2s3s3p4f4d4p4s2p3d “1” = p.e.l “s” = sublevel Orbital containing max 2 e- E config: 1s 1 Basic: 1 (this is what is in the C.R.T)

75. He:Li:Be:B: 1s2s3s3p4f4d4p4s2p3d 1s 2 1s 2 2s 1 1s 2 2s 2 1s 2 2s 2 2p 1 C: 1s 2 2s 2 2p 2 N: 1s 2 2s 2 2p 3 O: 1s 2 2s 2 2p 4 F: 1s 2 2s 2 2p 5 Ne: 1s 2 2s 2 2p 6 Na: 1s 2 2s 2 2p 6 3s 1 Mg: 1s 2 2s 2 2p 6 3s 2 Al: 1s 2 2s 2 2p 6 3s 2 3p 1 Hund’s Rule!

76. Draw the electron configuration for Chlorine: 1s2s3s3p4f4d4p4s2p3d Basic E- config: 2-8-7 E-config: How many valence electrons?

77. Sometimes, we use orbital diagrams. Orbital diagrams use boxes to represent the each orbital found in a sublevel. 2 electrons/box just like 2 electrons/orbital. S= 1 box P= 3 boxes D= 5 boxes F= 7 boxes They are useful when determining the number of Unpaired electrons!!!

78. Ex: Orbital diagram of chlorine: Basic e-config: 2-8-7 Expanded:1s 2 2s 2 2p 6 3s 2 3p 5 Orbital Diagram: 1s 2 2s 2 2p 6 3s 2 3p 5

79. After the element Argon: 2-8-8 (18 total e-) the electrons will be placed out of order. The P.E.L’s will start to overlap one another in an atom to stabilize the atom. For element larger than Argon: we use the “Diagonal Rule” to predict the order or e- filling.

80. Diagonal Rule 7s 6s 5s 4s 3s 2s 1s 7p 6p 5p 4p 3p 2p 7d 6d 5d 4d 3d 7f 6f 5f 4f Electrons will follow the arrows to fill p.e.l’s. If you look, electron will fill 4s before 3d, as you might expect. This is due to shell overlap to stablize.

81. Electron Configuration for K: Electron Configuration for K: 19 electrons: must use diagonal rule! 1s2s3s3p4f4d4p4s2p3d How many valence electrons?

82. Electron Configuration for Fe: 26 electrons: must use diagonal rule! 1s2s3s3p4f4d4p4s2p3d How many valence electrons?

83. Lewis Dot Structures Lewis Dot structures are a way of representing an element and their valence electrons. This is useful when we get to bonding to show the interaction between nuclei and electrons. Lewis Dot Diagrams: 2 parts Kernel: The nucleus and all non-bonding electrons Dots: The valence electrons

84. Steps for Writing Lewis Dot Structures 1. Write the element symbol. Called “kernel.” Represents all protons, neutrons, non-valence e- 2. Use dots to represent the valence e-. These go around kernel. 3. Place 2 dots together first. Then place dots around kernel, placing one on each side. Don’t double up until each side has at least 1.

85. How many valence e-?2 Lewis Dot: Mg

86. How many valence e-?5 Lewis Dot: N C C C C C

87. How many valence e-?7 Lewis Dot: Cl C C C C C C

89. The principle energy levels that the electrons are house in, are associated with certain levels of energy. The PEL closest to the nucleus has the least amount of energy, while the farther away PEL’s have the most amount of energy. If we feed the electrons energy in the form of heat or electricity, we can force them to jump into a higher PEL. They get “excited”

90. Electrons can gain energy and jump up to a higher principle energy level. We call these electrons in an “excited” state However, they are very unstable. Stay for a short period of time, released energy to fall back down to their “ground” state.

91. Excited vs. Ground State When the electrons release the energy to drop from excited to ground state, this energy is LIGHT energy. Each different color light corresponds with a different amount of energy or a different “fall” from one PEL to another. The energy that they absorb and emit is called “ QUANTA ”. Packets of Light “ QUANTA ”. Packets of Light

92. How to recognize Excited state electron configurations appear as if a mistake has been made. Always check to make sure it has the right amount of electrons for the given element, and then look for a mistake. Normal:Excited: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 6

94. Because each element has its own unique electron configuration, the color of light given off is unique to that element. Flame Test Lab! If we were to view this light through a If we were to view this light through a spectroscope, it would break the light up into its component parts. This is called the bright line spectrum. spectroscope, it would break the light up into its component parts. This is called the bright line spectrum.

95. Spectroscope: A devise that contains a prism and used to separate light into component colors. (Roy G. Biv)

96. Bright Line Spectrum: Unique set of wavelengths ( ) of light for each element. These unique wavelengths and spectrum of light are produced because each element has a unique electron arrangement. If we have a mixture of elements, we can identify them, using the bright line spectrum.

98. The diagram shows the characteristic spectral line patterns of four elements. Also shown are spectral lines produced by an unknown substance. Which pair of elements is present in the unknown? 1.lithium and sodium 2.sodium and hydrogen 3.lithium and helium 4.helium and hydrogen