Atomic Theory of the Elements for High S

High School

1. Atomic Theory The History

2. Democritus 460-370 B.C. Atom is a tiny indivisible particle of matter which cannot be divided. Word “atom” came from the Greek term atomos which means indivisible.

3. Aristotle 384 BC – 322 BC Disagreed with Democritus’ ideas about atoms and most Greeks agreed. Determined there were four elements: earth, air, wind and fire.

4. Antoine Lavoisier 1743-1794 Law of Conservation of Mass Matter is not created or destroyed in a chemical reaction

5. John Dalton 1766-1844 Important theories, but there were some inaccuracies that were later clarified. Defined an atom as: The smallest particle of an element that retains the properties of that element. Example: There are 1.2x10 18 atoms in a grain of salt.

6. Dalton’s Atomic Theory of Matter Matter is composed of small particles (atoms). Atoms of a certain element are identical. Atoms cannot be divided into smaller particles. Different atoms combine in simple whole-number ratios to form compounds Atoms are rearranged in a chemical reaction.

7. Quiz Democritus described the ___ as a tiny indivisible particle. The Atomic Theory was devised by ____. It states that matter is made of small particles called ___. These cannot be ____. All atoms are ___ in size, etc. In a chemical reaction atoms are ____ and combine in ___number ratios.

8. Quiz Continued… Dalton’s theory was important but ____. The smallest particle of an element that retains the properties is ____.

9. J.J. Thomson 1856-1940 Worked with cathode ray tubes to find the charge:mass ratio for particles. Plum Pudding Model Believed that the (-) charges were distributed throughout a uniform positive charge.

10. Plum Pudding Model

11. Robert Millikan Oil Drop Experiment Determined the charge and calculated the mass of the electron. Mass = 9.11 x 10 -28 g 1/1840 mass of hydrogen (0 Atomic Mass Units)

12. Millikan Oil Drop Experiment

13. Earnest Rutherford Gold Foil Experiment Alpha particles were shot through thin gold foil. Most of the particles passed straight through. About 1 in 8000 particles was deflected. This showed that matter is mostly empty space, but there is a small, dense nucleus that is positively charged.

14. Rutherford Gold Foil Experiment

15. The Atomic Scale Most of the mass of the atom is in the nucleus (protons and neutrons) Electrons are found outside of the nucleus (the electron cloud) Most of the volume of the atom is empty space “q” is a particle called a “quark”

16. EQ #1 What are the position, charge and relative size of the subatomic particles?

17. The Subatomic Particles: Particle Symbol Location Charge Relative Mass Electron e - Outside Nucleus - 1 * 0 AMU (1/1840) Proton p + Nucleus + 1 1 AMU Neutron n ° Nucleus 1 AMU

18. AMU = Atomic Mass Unit These are the units used because the mass of atoms is so small. 1 p + = 1.007 276 amu (1 amu) 1 n = 1.008 665 amu (1 amu) 1 e - = 0.000 549 amu (0 amu)

19. The Atom Cloud of fast moving electrons travel through the empty space surrounding the nucleus. If the atom is neutral: Number protons = number electrons Nucleus contains protons & neutrons. (Except: H atom has 1 proton & 0 neutrons) Neutrons separate (+) charged protons .

20. Protons Protons determine an elements identity. Changing the number of protons creates a different element with a different atomic number. Element Atomic # # Protons Carbon 6 6 Phosphorus 15 15 Gold 79 79

21. Identify the number of Protons: Helium = 2 Protons Neon = 10 Protons

22. The Atomic Number also gives us the number of electrons if the atom is neutral. # protons (+) = # electrons (-) How many protons does lithium have? Electrons? Answer: 3 protons and 3 electrons How many protons does oxygen have? Electrons? Answer: 8 protons and 8 electrons If electrons are gained or lost, the atom is then an ion.

23. APE A tomic Number = P rotons = E lectrons (if neutral)

24. Quiz Tell whether the following describes a proton, neutron, or electron: +1 charge Found in nucleus Has a mass of 1 amu 0 charge Negligible (1/1840) mass (0 amu) -1 charge If neutral, the number protons = # _____ Particles identifies the element

25. EQ #2 How is an Element’s Identity Determined?

26. EQ #5 How does the abundance of various isotopes affect an atom’s mass?

27. Mass Number Mass Number is the number of protons and neutrons in the nucleus of an atom. Electrons are not included (mass of 0 amu) Atom Protons Neutrons Electrons Mass Number Oxygen-18 (O-18) 8 10 8 18 Arsenic-75 (As-75) 33 42 33 75 Phosphorus-31 (P-31) 15 16 15 31

28. Isotopes Atoms of the same element having different numbers of neutrons. These do have the same number of protons and electrons. These have different masses since there is a different number of neutrons. What element is shown in the diagram? How many protons and electrons in each isotope? What is the mass of each?

29. Atomic Mass This is the weighted average mass of all isotopes of a given element. Boron has 2 isotopes. Boron-10 and Boron-11 (B-10 and B-11) Which isotope is more common?

30. If a mass number is not provided, then round the atomic mass, and then subtract the atomic number to find the number of neutrons. How many protons, neutrons and electrons in Lithium?

31. What is the most abundant isotope for carbon?

32. COMPARE 3 ISOTOPES OF HYDROGEN: H-1 H-2 H-3 How many p+ for each? What is the atomic #? How many e - ? What is the mass# How many n o ? What is the atomic mass for H? Which isotope?

33. What is the most abundant isotope for Hydrogen?

34. Isotopic Notation 14 C or 14 C 6 Used to show mass # (top) and atomic # (bottom) Find atomic #, number protons, number of electrons. How many neutrons? Top – bottom = 14 – 6 = 8 Ans. 1) 6,6,6 C-14 is used to date rock art, etc.

35. Isotopic Notation What is another way to write this? C-12 Carbon-12

36. ATOMIC MASS IS A WEIGHTED AVERAGE: To find a weighted average: (% as a decimal) (Mass 1) + (% as a decimal) (Mass 2) Weighted Average

37. Weighted Average Find the average mass of football team if; 90% weigh 200 lbs. 10% weigh 180 lbs. Ave. mass = (0.90)(200) + (0.10)(180) = 180 + 18.0 = 198 lbs.

38. ATOMIC MASS OF ELEMENT – Weighted average mass of the isotopes of that element. Isotopes % Abundance Atomic Mass Cl-35 75.770% 34.969 amu Cl-37 24.230% 36.966 amu At.Mass = (% Cl-35)(Mass) +(% Cl-37)(Mass) = (0.75770)(34.969) + (0.24230)(36.966) = 26.496 amu + 8.957 amu = 35.453 amu Check answer on Periodic Table √ Ans. Closest to Cl-35 (76% abund.)

39. EQ #5 How does the abundance of various isotopes affect an atom’s mass?

40. The Atomic Number also gives us the number of electrons if the atom is neutral. # protons (+) = # electrons (-) How many protons does lithium have? Electrons? Answer: 3 protons and 3 electrons How many protons does oxygen have? Electrons? Answer: 8 protons and 8 electrons If electrons are gained or lost, the atom is then an ion.

41. APE A tomic Number = P rotons = E lectrons (if neutral)

42. FINDING # ELECTRONS WHEN ATOMS ARE NOT NEUTRAL Neutral atoms: # electrons = # protons Atoms become charged (ionized) when they gain or lose electrons

43. Negative Ions Gain of electrons – negative charge Ex. Cl has 17 p + 17 e - (neutral) Cl - 17 p + 18 e - (gained 1 electron)

44. Positive Ions Formed by loss of electrons Ex. Na has 11 p + 11 e - (neutral) Na + 11 p + 10 e - ( lost 1 electron) Al 3+ 13 p + 10 e - ( lost 3 electrons)

45. Practice Find Protons and Electrons Mg 12 p + 12 e - (neutral) Ca 2+ 20 p + 18 e - (lost 2 e - ) Br - 35 p + 36 e - (gained 1 e - ) P 3- 15 p + 18 e - (gained 3 e - )

46. Practice Find protons, electrons and neutrons 41 Ca or Ca-41 20 20 p + 20 e - 41-20 = 21 n 41 Ca 2+ 20 p + 20-2 = 18 e - 41-20 = 21 n 127 I 1- 53 53 p + 53 + 1 = 54 e - 127 - 53 = 74 n

47. Atomic Theory The End