Chemistry EOC TIPS

1. Chemistry EOC TIPS Remember, label your periodic table with the positive and negative charges before you begin your test. Remember, to use your reference page to find formulas and constants Remember to do all of the problems that you know how to do first, and then go back and do the ones you don’t know. Remember, the group numbers tell you the number of valence electrons. You have 75 minutes to complete your test.

2. Labeling Your Reference Page • Label the metals in Groups 1-3 with their positive charges, and the non-metals in 14-17 with their negative charges. • Draw the periodic trend arrows for atomic radius- the other two trends (Electronegativity and Ionization Energy are opposite). • 1kg = 1L ( for molality problems) • Draw the Mole Wheel

3. THE BIG SEVEN- DIATOMIC ELEMENTS *There are 7 elements that are not found alone in nature: N2, O2, F2, Cl2, Br2, I2, and H2 • Diatomic: • Too unstable to occur on their own, occur in pairs. • Example:

4. History of the Atom – Ch. 3 PPT

5. Democritus (400 B.C.) • A Greek philosopher • Was the first person to thinkabout an atom’s existence. • Believed that matter was composed of tiny indivisible particles called atoms. “atomos” He had no experimental evidenceto support his thoughts. Hmmm… atoms…

6. John Dalton (1803) • A meteorologist • Unlike Democritus, he had experimental evidence to support his theory. • Dalton had fourmajor points (postulates) to his theory.

7. Joseph John (J.J.) Thompson) • In the tube was an inert gas, and two plates, a positiveand a negative. • The particles in the gas were attracted to the positiveplate. • Therefore, the particles MUST have anegativecharge. (Opposites attract.) Cathode Ray Tube Experiment

8. Plum Pudding Model - 1897 • Discovered the electron. • From his experimental evidence, he believed that the atom was a solid positive sphere with electrons shoved into the sides of it. • His model was said to resemble a popular English dessert called Plum Pudding, and so his model was deemed the “Plum Pudding Model.”

9. Ernest Rutherford • Used the gold foil experiment to discover the nucleus. • Shot high energy beam of alphaparticlesinto gold foil.

10. Ernest Rutherford Conclusions The atom is mostly empty space. The alpha particle came close to something small and positive (nucleus). The alpha particles hit a small, very dense, and positively charged center (nucleus).

11. Rutherford’s Planetary Model • The problem with this model is that it doesn’t make sense. • If the electrons are circling around the positively charged nucleus, why don’t the opposite charges attract?

12. Eugene Goldstein (1850-1930) • Goldstein discovered theproton. James Chadwick (1932) Chadwick discovered theneutron.

13. Arranging elements in order of increasing atomic mass worked relatively well, but some discrepancies resulted: For example: K and Ar. The mass of Potassium is less than that of Ar. Today, elements on the periodic table are arranged by increasing Atomic Number (number of protons) Mendeleev’s Periodic Law

14. Elements are arranged in order of increasing atomic number and show a periodic repetition of properties Modern Periodic Law

15. The atom is made up of protons and neutrons in the nucleus and electrons orbiting around it. ONLY electrons can be added or subtracted from an atom When this occurs the atom becomes an ion Loses electrons (metal) = cation (+) because it has less negative charges Gains electrons (non-metal) = anion (-) it has because more negative charges Ions can be distinguished from atoms by writing the ion charge as a superscript in the symbol Ions

16. Isotopes • Atoms of an element with the same number of protons, but different number of neutrons. • They are chemically alike. • Have different mass numbers. • Written like this: • Element–Mass Number • Ex: C-11 C-12 C-13

17. Examples: Neutral hydrogen isotopes Hydrogen has 3 different atoms H-1 H-2 H-3 1 proton 1 proton 1 proton 1 electron 1 electron 1 electron 0 neutrons 1 neutron 2 neutrons Isotopes are named by their atomic masses.

18. Isotopes that are radioactive Radioactive isotopes are formed from unstable nuclei. They release radiation as they decay and change into other isotopes of a given element Used in smoke detectors, food irradiation and cancer treatments Radiation comes in three forms: alpha, beta, gamma Radioisotopes The radiation is used to kill bacteria in food, prolonging its shelf-life

19. Radiometric dating: using the known half-life of an unstable element (time to change to more stable form), we can calculate the amount of time that has elapsed since a known level of isotope existed The most widely known example is radiocarbon dating used to determine the age of carbon based materials (trees, etc.) Cancer treatments – Isotopes are injected into the patients cancer cells. The isotopes release radiation which kills nearby cancer cells What are Isotopes used for?

20. 3 Types of Radiation • Alpha ( α) – emits 2 protons and 2 neutrons during radioactive decay. Releases a helium nucleus. Reduces the atomic number by two and the mass number by four. They are slow and can be stopped by paper. • Beta (β) – A beta particle (electron) is released from the nucleus, causing the atomic number to be reduced by one, and the mass number stays the same. They can travel through paper but not aluminum foil. • Gamma (γ) – High energy magnetic waves that are released when the nucleus changes from an excited to a ground state. Does not affect the atomic number or the mass. Most powerful form of radiation.

21. 226 222 Ra Rn 88 86 4 He 2 Alpha Decay

22. + A - 4 Y A X Z - 2 Z 4 4 226 222 He He Ra Rn + 2 2 88 86 Alpha Decay

23. 222 Rn + 86 A Y Z 222 218 4 4 4 Rn Po He He He + 86 84 2 2 2 Alpha Decay

24. A X + 230 Th Z 90 234 230 4 4 4 U Th He He He + 92 90 2 2 2 Alpha Decay

25. 230 230 Th Th + A Y 90 90 Z 226 4 4 4 Ra He He He + 88 2 2 2 Alpha Decay

26. A 218 X Po + 214 Pb 84 Z 82 214 4 4 4 Pb He He He + 82 2 2 2 Alpha Decay

27. Beta Decay A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when a neutron changes into a proton and an electron.

28. Beta Decay A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when a neutron changes into a proton and an electron.

29. Beta Decay As a result of beta decay, the nucleus has one less neutron, but one extra proton. The atomic number, Z, increases by 1 and the mass number, A, stays the same.

30. 218 218 Po At 84 85 0 b -1 Beta Decay

31. A A 0 0 b b X Y + Z Z + 1 -1 -1 218 218 Po Rn + 84 85 Beta Decay

32. 210 A 0 0 b b Bi Y + 83 Z -1 -1 210 210 Bi Po + 83 84 Beta Decay

33. A 210 0 0 b b X Pb + Z 82 -1 -1 210 210 Tl Pb + 81 82 Beta Decay

34. 234 A 0 0 b b Th Y + 90 Z -1 -1 234 234 Th Pa + 90 91 Beta Decay

35. A 214 0 0 b b X Bi + Z 83 -1 -1 214 214 Pb Bi + 82 83 Beta Decay

36. 7.2 Half-life • It can be difficult to determine the ages of objects by sight alone. • Radioactivity provides a method to determine age by measuring relative amounts of remaining radioactive material to stable products formed. • See pages 302 - 304

37. 7.2 Half-life • Carbon dating measures the ratio of carbon-12 and carbon-14. • Stable carbon-12 and radioactive carbon-14 exist naturally in a constant ratio. • When an organism dies, carbon-14 stops being created and slowly decays. • Carbon dating only works for organisms less than 50 000 years old. • Using carbon dating, these cave paintings of horses, • from France, were drawn 30 000 years ago. • See pages 302 - 304

38. The Rate of Radioactive Decay • Half-life measures the rate of radioactive decay. • Half-life = time required for half of the radioactive sample to decay. • The half-life for a radioactive element is a constant rate of decay. • Strontium-90 has a half-life of 29 years. If you have 10 g of strontium-90 today, there will be 5.0 g remaining in 29 years. • See pages 305 - 306

39. The Rate of Radioactive Decay • Decay curves show the rate of decay for radioactive elements. • The curve shows the relationship between half-life and percentage of original substance remaining. • The decay curve for strontium-90 • See pages 305 - 306

40. Half – Life Problem • Radioactive Half-Life Formula Questions: • 1. If the half-life of 100.0 grams of a radioactive isotope is 8 years, how many grams will remain in 32 years? • Answer: • To answer this question, there is no need to solve for the radioactive decay equation. If 32 ÷ 8 = 4, then the material will go through 4 half-lives. • 6.25g

41. 30.3 Fusion reactions • A fusion reaction is a nuclear reaction that combines, or fuses, two smaller nuclei into a larger nucleus. • It is difficult to make fusion reactions occur because positively charged nuclei repel each other.

42. 30.3 Fission reactions • A fission reaction splits up a large nucleus into smaller pieces. • A fission reaction typically happens when a neutron hits a nucleus with enough energy to make the nucleus unstable.

43. Electron Configuration – Ch. 4 • 2n2 is the equation that tells you how many electrons can be found on each energy level. • Ex: 3rd Energy Level = 2(3)2 = 62 = = 36 electrons. • You can also count two electrons for each box on the periodic table in that row.

44. Silicon – 1s22s22p63s23p2

45. The 4 types of orbitals that electrons can be found in

48. How many electrons are found in each orbital

49. Periodic Trends – Chapter 5

50. PERIODIC TRENDS - ATOMIC RADIUS INCREASE INCREASES