1. Atomic Theory Model History and Structure

2. I. Models of the Atom A. The Evolution of Atomic Models 1. He believed that there had to be a basic building block that made up all other matter. 2. Democritus believed the atom was it – smallest particle of matter. a. All matter consists of invisible particles called atoms. b. Atoms are indestructible. c. Atoms are solid but invisible. d. Atoms are homogenous. e. Atoms differ in size, shape, mass, position, and arrangement. – ->Solids are made of small, pointy atoms. – ->Liquids are made of large, round atoms. – ->Oils are made of very fine, small atoms that can easily slip past each other.

3. I. Models of the Atom A. The Evolution of Atomic Models 3. There are four major models of the atom that have been developed from John Dalton theory. 4. Dalton Atomic Theory a. He theorized that an atom was indivisible, uniformly dense sphere. b. He theorized that all atoms of the same element have the same mass and the same chemical behaviors. c. He theorized that atoms of different elements have different chemical behaviors. d. He theorized that atoms of different elements combine to form compounds. (Example — H 2 O)

4. I. Models of the Atom A. The Evolution of Atomic Models 5. J.J. Thomson realized that the accepted model did not take electrons into account. a)J.J. Thompson devised an experiment to determine the nature of the cathode ray. b)He built a cathode ray tube and placed a fluorescent screen at the end that would glow when struck by charged particles. c)When the beam was normal, the center of the screen would glow but, when altered with a magnet or charged plates, the glow would move in the direction that the beam was altered. d)He concluded that the direction of the beam was determined by the charge of the plate. e)He concluded that the particles in the cathode ray are subatomic particles that are found in all atoms. f)He is credited with the discovery of the negatively charged particles called electrons. 1.He is credited with the discovery of the negatively charged particles called electrons. 2.He theorized that the atom is a dense sphere with a positive charge and also contains negative charged particles. 3.His model is also known as the Plum Pudding model.

5. Cathode Ray Tube

6. I. Models of the Atom A. The Evolution of Atomic Models 6. Robert A. Millikan obtained the first accurate measurement of an electron charge. a. Using a brass atomizer, he sprayed oil drops into an apparatus with charged plates inside (electrons were transferred to oil drops). b. The charge plates were set to offset the force of gravity. c. When the forces were equal, the drops were stationary (the drops did not move). d.An electron carries exactly one unit of negative charge, and its mass 1/1840 the mass of a hydrogen atom. 7. Ernest Rutherford expanded on Thomson’s theory. a. The atom has a very dense center of positive charge called the nucleus. b. The nucleus contains the protons for the atom and make up more than 99.9% of its mass. c.The electrons surround the nucleus. 8. Evidence for a positively charged particle was found by E. Goldstein. a.He observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. b.He called them canal rays and concluded that they were composed of positively charged particles. c.We call these particles protons. d.The first evidence of the third particle was discovered by Walter Bothe and later James Chadwick repeated Bothe’s work. e.They found a high energy particles with no charge and the same mass as the proton. f.These particles are called neutrons.

7. Brass Atomizer and Oil Drop

8. I. Models of the Atom A. The Evolution of Atomic Models 9. Ernst Rutherford designed an experiment to test Thompson’s Model. a He used alpha particles to bombard targets made of thin gold foil. b. A fluorescent screen was placed around the gold foil to detect the particles after they struck the target. c.He expected that the particles should uniformly pass through the foil undisturbed and some of the particles did pass through but other were deflected. d.He realized the explanations that accounts for the deflection. 1.The atom has a very dense center of positive charge called the nucleus. 2.The nucleus contains the protons for the atom and make up more than 99.9% of its mass. 3.The electrons move around the nucleus.

9. Rutherford’s Gold Foil Experiment Stats...Stats... 98% of particles went straight through (expected) 98% of particles went straight through (expected) 2% of particles deflected at large angles 2% of particles deflected at large angles 0.01% of particles deflected straight back (canon balls & tissue!) 0.01% of particles deflected straight back (canon balls & tissue!)

10. I. Models of the Atom A. The Evolution of Atomic Models 10. Niels Bohr proposed a model in which the electrons move around the nucleus. a. He theorized that the electron orbits the nucleus. b. He theorized that the orbits were different energy levels that the electrons travel in and can be excited to a high energy level. c. He theorized that the electrons did not lose energy and fall into the nucleus. (The weakness in Rutherford’s theory.) 11. A quantum of energy is the amount of energy required to move an electron from its present energy level to the next higher one. (Also called a quantum leap)

11. I. Models of the Atom B. The Quantum Mechanical Model 1. Erwin Schrödinger related the amplitude of the electron wave,  (psi), to any point in space around the nucleus. 2. His equation treated the electron as a wave and developed an equation to describe this behavior. 3. The quantum mechanical model comes from the mathematical solutions to Schrödinger equation.

12. I. Models of the Atom B. The Quantum Mechanical Model 4. The quantum mechanical model does not define an exact path for the electron to take around the nucleus but instead estimates a probability of finding the electron in a certain position. 5. Since the volume occupied by an electron is somewhat vague, it is better to refer to an electron cloud. Plum Pudding Rutherford Rutherford-Bohr Quantum

13. II. Distinguishing Between Atoms A. Atomic Number 1. The atomic number is the number of protons in an atom. 2. Because the atom is electrically neutral, the number of electrons is equal to the number of protons. 3. The number of protons determines the identity of the element. 4. To solve for the number of neutrons, subtract the atomic mass by the atomic number.

14. Characteristics of Elements K 19 Potassium 39.098 Atomic Number Element Symbol Element Name Atomic Mass

15. II. Distinguishing Between Atoms B. Mass Number and Isotopes 1. The proton and neutron are equal in mass. 2. The mass of the electron is extremely small, so most of the mass is in the nucleus. 3. It is possible to discuss the mass of one atom, however chemist use the masses of a large groups of atoms. 4. The way to represent this is with the symbol of the element and the mass as a superscript and the atomic number as a subscript. ( Oxygen 16 8 O) 5. It can also be written as oxygen -16. 6. An element that has the same atomic number but a different mass is called an isotope. 7. Isotopes are chemically alike because they have identical numbers of protons and electrons which are responsible for reactivity. 8. Example Carbon-12 and Carbon-14

16. Isotopes 22 22 X 12 12 +3 +3 22 22 X 10 10 25 25 X 10 10 -1 -1 Neon - 20 Neon - 20 Neon - 22 Neon - 22 Fluorine - 20 Fluorine - 20 Isotopes: atoms of the same element with different atomic masses. Isotopes: atoms of the same element with different atomic masses. - different # of n 0 !!!- different # of n 0 !!! Three isotopes of Carbon: Three isotopes of Carbon: Carbon - 12 (6p +, 6n 0 ) element of lifeCarbon - 12 (6p +, 6n 0 ) element of life Carbon - 13 (6p +, 7n 0 ) extremely rare Carbon - 13 (6p +, 7n 0 ) extremely rare Carbon - 14 (6p +, 8n 0 ) radioactive…carbon datingCarbon - 14 (6p +, 8n 0 ) radioactive…carbon dating Note: atomic # will NEVER change in isotopes… only mass and # of n 0 do!Note: atomic # will NEVER change in isotopes… only mass and # of n 0 do! Which of the following are isotopes of the same element?Which of the following are isotopes of the same element?

17. Average Mass of Isotopes Isotopes are naturally occurring. Isotopes are naturally occurring. The mass # of an element (periodic table) is the weighted avg. of allisotopes that exist in nature. The mass # of an element (periodic table) is the weighted avg. of all isotopes that exist in nature. - abundance of isotope is just as important as mass! - abundance of isotope is just as important as mass! Ex... Ex... Natural copper (Cu) consists of 2 isotopes …Natural copper (Cu) consists of 2 isotopes … Copper - 63 (mass = 62.930 g/mole) @ 69%Copper - 63 (mass = 62.930 g/mole) @ 69% Copper - 65 (mass = 64.930 g/mole) @ 31%Copper - 65 (mass = 64.930 g/mole) @ 31% To calculate avg. mass... To calculate avg. mass... Step 1 : mass x abundance for each isotopeStep 1 : mass x abundance for each isotope Step 2 :add the two values from step 1 togetherStep 2 :add the two values from step 1 together 62.93 x.69 = 43.42 43.4262.93 x.69 = 43.42 43.42 64.93 x.31 = 20.13 +20.1364.93 x.31 = 20.13 +20.13 63.55 g/mole

18. Average Mass of Isotopes The average mass of an element is closest to the isotope that is mostplentiful in nature. The average mass of an element is closest to the isotope that is most plentiful in nature. Ex... Ex... Three isotopes of Oxygen:Three isotopes of Oxygen: Oxygen - 16 Oxygen - 16 99. 759% Oxygen - 17 Oxygen - 17 0.037% Oxygen - 18 Oxygen - 18 0.204% The avg. mass (from P.T.) is closest to 16, therefore, Oxygen-16 is the isotope that is most abundant in nature.

19. Characteristics of Elements Atomic Number : Number of p + in an atom Atomic Number : Number of p + in an atom identifies elementidentifies element (change atomic # = change of element). # p + = # e- in neutral atom# p + = # e- in neutral atom (+) charge = less e- than p +(+) charge = less e- than p + (-) charge = more e- than p +(-) charge = more e- than p + Atomic mass:Atomic mass: (a.k.a. Mass Number) mass of the nucleusmass of the nucleus p + + n 0p + + n 0 units are a.m.u. (atomic mass unit)units are a.m.u. (atomic mass unit)

20. II. Distinguishing Between Atoms C. Atomic Mass and Subatomic Particles 1. There are two ways of determining masses for atoms of other elements a. Reacting the standard element with the element to be determined b. Mass Spectrometer. 2. Using a mass spectrometer, we can determine the relative amounts and masses of the nuclides for all isotopes of an element. 3. Chemist measure the mass of one atom in atomic mass units (AMU). 4. The mass of the atomic particles. a. electron = 9.109 x 10 -28 g = 0.000549 AMU b. proton = 1.672 x 10 -24 g = 1.00 AMU c. neutron = 1.674 x 10 -24 g = 1.00 AMU 5. This is called the atomic mass and is the average of the amounts and masses of all the isotopes of the element.

21. Subatomic Particles PROPERTIES OF SUBATOMIC PARTICLES PARTICLESYMBOL ELECTRICAL CHARGE RELATIVE MASS ACTUAL MASS (g) Electron e-e-e-e-1/1840 9.11 x 10 -28 Proton p+p+p+p++11 1.67 x 10 -24 Neutron n0n0n0n001

22. Forms of Atomic Symbols There are two ways to represent elements: There are two ways to represent elements: Symbol Form: Symbol Form: # X # atomic mass atomic # (# of p + ) element symbol # X atomic mass element symbol OR OR Shorthand Form: name of element followed by atomic mass. Shorthand Form: name of element followed by atomic mass. Ex... Ex... Aluminum - 27Aluminum - 27 Nitrogen – 14 Nitrogen – 14 Carbon – 14Carbon – 14 You can find mass number, atomic number, number of n 0, and number of e- with either notation! You can find mass number, atomic number, number of n 0, and number of e- with either notation!

23. Practice: Atomic Symbols There are two ways to represent elements: There are two ways to represent elements: Symbol Form: Symbol Form: Shorthand Form: Shorthand Form: name of element followed by atomic mass. Ex... Aluminum – 27 Ex... Aluminum – 27 Find the following elements on the Periodic Table: Beryllium, Copper, Sulfur, Neon and write them in both notations. # X # atomic mass atomic # (# of p + ) element symbol # X atomic mass element symbolOR

24. Practice:Atomic Symbols Using the symbol form for neutral elements:Using the symbol form for neutral elements: Symbol Form:Symbol Form: # X # atomic mass (# of p + ) atomic # element symbol Now find for each element the: Now find for each element the: atomic mass atomic mass atomic number atomic number # of p+ (same as atomic#)# of p+ (same as atomic#) # of e- (same as # of protons)# of e- (same as # of protons) # of n 0 (mass# - atomic#)# of n 0 (mass# - atomic#)

25. Atomic Calculations All mass of the atom is in the nucleus. All mass of the atom is in the nucleus. – only p + and n 0 are in the nucleus. – if you know the mass of any atom, you can find the # of n 0. – if you know the # of n 0 and the # of p+, you can find the mass. Ex... electrical charge on atom ( it is an ion) Ex... electrical charge on atom ( it is an ion) Manganese - 55 31 31P 15 15 -3 -3 element = element = Phosphorus atomic mass = __31 a.m.u.s atomic # = 15 # of p + =15 # of N 0 =16 # of e - =18 symbol = __ symbol = __ Mn atomic mass = __ atomic mass = __55 a.m.u.s atomic # = atomic # = 25 # of p + = 25 # of n 0 = 30 # of e - = 25

26. http://the-history-of-the- atom.wikispaces.com/Democritus http://the-history-of-the- atom.wikispaces.com/Democritus http://edtech2.boisestate.edu/lindabennett1/ 502/democritus.html http://edtech2.boisestate.edu/lindabennett1/ 502/democritus.html