Chemistry

1. Chemistry The Study of Matter Chemistry is the branch of science that deals with the composition, structure, and properties of matter as well as the changes it undergoes. Matter is any substance that occupies space and has mass. Your chair, desk, and table are composed of matter. (page 533)

2. Chemistry The Study of Matter Even the air you breathe is composed of matter. Matter exists in four states— solid, liquid, gas, and plasma (an ionized gas of which the Sun is made). The starting point for a systematic study of chemistry generally begins with an examination of the basic unit of matter, the atom. (page 533)

3. Chemistry The Study of Matter The Atom, the Basis of Matter In chemistry, atoms are the building blocks for matter. The atom is the smallest particle of an element that has the properties of that element. An element is a substance that occurs in nature and that cannot be broken down into a simpler substance. (page 533)

4. Chemistry The Study of Matter The Atom, the Basis of Matter Nearly 100 fundamental substances known as elements are known to occur in nature. A few elements have been produced synthetically by man. Atoms also form molecules. A molecule is the smallest part of a compound that can exist by itself. A molecule consists of two or more atoms joined together chemically. (page 533)

5. Chemistry The Study of Matter The Atom, the Basis of Matter

6. Chemistry The Study of Matter The Atom, the Basis of Matter

7. Chemistry The Study of Matter The Atom, the Basis of Matter

8. Chemistry The Study of Matter The Atom, the Basis of Matter In the early 19th century, only a few elements were known to exist. According to the theory of John Dalton, an atom cannot be made, destroyed, or divided; and atoms of the same element are alike. This concept became known as atomic theory. Later physicists discovered that the nucleus of an atom can be split by bombarding it with neutrons, a process known as nuclear fission. (page 534)

9. Chemistry The Study of Matter The Atom, the Basis of Matter John Dalton

10. Chemistry The Study of Matter The Atom, the Basis of Matter A Russian chemist, Dmitri Mendeleyev, constructed a table, known as the periodic table, by which he calculated the atomic weights of the different elements. The elements are identified by symbols taken largely from Latin names for the elements. Hydrogen is the lightest known element, having only one proton and was, therefore, assigned the atomic number 1. (page 534)

11. Chemistry The Study of Matter The Atom, the Basis of Matter Dmitri Mendeleyev

12. Chemistry

13. Chemistry

14. Chemistry The Study of Matter The Atom, the Basis of Matter An atom of oxygen, an abundant gas on Earth, has a mass 16 times that of a hydrogen atom; therefore, oxygen was given an atomic mass of 16. Oxygen is the eighth lightest element and is assigned the atomic number 8. (page 534)

15. Chemistry The Study of Matter The Atom, the Basis of Matter Dalton's and Mendeleyev's discoveries were the most significant in the field of chemistry since that of Antoine-Laurent Lavoisier, a French chemist who identified oxygen as the key element that supports combustion. (page 534)

16. Chemistry The Study of Matter The Atom, the Basis of Matter Atomic Structure Scientists have learned a great deal about atoms since Dalton's time. For example, an atom is composed of a nucleus with electrons that surround it. The nucleus, located in the center of the atom, is made up of protons and neutrons. (page 534)

17. Chemistry The Study of Matter The Atom, the Basis of Matter Atomic Structure A proton is a positively charged particle. An element's atomic number is determined by the number of protons it has. Because hydrogen has only one proton in its nucleus, it has an atomic number of 1. A neutron has a mass nearly equal to that of a proton but has no charge at all. The nucleus has a positive charge, determined by the number of protons it contains. The nucleus provides the mass number for an element. (page 534)

18. Chemistry The Study of Matter The Atom, the Basis of Matter Atomic Structure An electron is a negatively charged particle. Electrons occupy an orbit, or shell, that surrounds the nucleus. Each shell can hold only a fixed number of electrons. It is the number of shells that distinguishes one element from another. The greater the number of shells with orbiting electrons that an element has, the greater its atomic number. (page 534)

19. Chemistry The Study of Matter The Atom, the Basis of Matter Atomic Structure

20. Chemistry EXERCISE 1 Atomic Structure Directions: Match each term on the right with the correct description on the left. (page 535) 1. ________ the second lightest element; a. oxygen contains two protons in its nucleus 2. ________ a negatively charged particle b. neutron 3. ________ the part of an atom that determines c. proton an element's mass 4. ________ a particle that has no charge d. helium 5. ________ a positively charged particle e. electron 6. ________ an element containing eight protons f. nucleus in its nucleus

21. Chemistry Nuclear Energy The nucleus of every atom contains an almost unimaginable amount of potential energy. The protons that are locked together are all positive and naturally repel each other. It takes the strongest force in the universe, nuclear force, to keep those subatomic particles locked together. (page 536)

22. Chemistry Nuclear Energy Nuclear fission

23. Chemistry Nuclear Energy Nuclear fusion

24. Chemistry Nuclear Energy Nuclear fission and fusion

25. Chemistry Nuclear Energy Science has been able to unlock and capture this energy by splitting larger atoms (those with the greatest number of protons) by firing a neutral neutron at the atom. This process of splitting the larger atoms is nuclear fission. The fuel for this reaction is uranium because of the great size of its nucleus and its unstable qualities. (page 536)

26. Chemistry Nuclear Energy When a material is unstable and able to release radiation it is said to be radioactive. This radioactive material is made into pellets that are held by fuel rods placed in a heavily shielded nuclear reactor. (page 536)

27. Chemistry Nuclear Energy

28. Chemistry Nuclear Energy The process of regulating the release of the nuclear energy requires that the fuel rods remain partially covered with control rods. These control rods prevent free neutrons from splitting too many uranium atoms in an uncontrolled explosion. (page 536)

29. Chemistry Nuclear Energy Radioactivity and Environmental Protection One of the dangers of nuclear energy is that such an explosion could release radioactive materials into the environment, causing serious and extensive contamination of radioactivity to any living organisms, plants and animals in the vicinity. (page 536)

30. Chemistry Nuclear Energy Radioactivity and Environmental Protection Chernobyl

31. Chemistry Nuclear Energy Radioactivity and Environmental Protection Chernobyl

32. Chemistry Nuclear Energy Radioactivity and Environmental Protection Chernobyl

33. Chemistry Nuclear Energy Radioactivity and Environmental Protection Chernobyl

34. Chemistry Nuclear Energy Radioactivity and Environmental Protection One such explosion occurred at a Ukranian nuclear power plant, Chernobyl, in the early 1980s. A combination of poor operator judgment and a tight testing schedule created the conditions that caused too many of the fuel rods to be exposed. The overwhelming heat from the reaction melted through the containment walls, and an explosion sent radioactive particles and gases outside to the nearby forest and town. (page 536)

35. Chemistry Nuclear Energy Radioactivity and Environmental Protection To stop the fire and prevent further leakage, the entire reactor was encased in cement, which is now referred to as the sarcophagus (a stone coffin). Local animals that were contaminated as well as the entire nearby forest and even construction equipment used during the cleanup had to be buried as well. (page 536)

36. Chemistry Nuclear Energy Radioactivity and Environmental Protection Evacuation of the residents of the town near the reactor did not allow the packing of personal belongings. The town remains empty to this day, and the objects left behind convey a very eerie "ghost town" effect. (page 536)

37. Chemistry Nuclear Energy Radioactivity and Environmental Protection The United States also has experienced the fear of a near disaster. A nuclear power plant at Three Mile Island, located in New Jersey, sprang a leak of cooling water. This leak allowed the reactor to become very hot. (page 536)

38. Chemistry Nuclear Energy Radioactivity and Environmental Protection Three Mile Island

39. Chemistry Nuclear Energy Radioactivity and Environmental Protection The American reactor, however, was equipped with an automatic shut-off system that was activated when the recorded temperature exceeded maximum capacity. There was no leakage of radioactive materials, and nuclear-energy advocates explain that this fact proves that the automatic system keeps nuclear power safe. (page 536)

40. Chemistry Nuclear Energy Radioactivity and Environmental Protection These advocates still do not have an answer to the biggest concern nuclear-energy opponents have: the safe disposal of radioactive wastes. Currently these wastes are sealed in large barrels and are transported to empty underground mines that are reinforced with a lining to protect the environment. (page 536)

41. Chemistry EXERCISE 2 Nuclear Energy Directions: Read the passage below and choose the best answer for each of the following items. You may need to refer to the periodic table shown on page 541. Nuclear energy may be released in two ways: by fission and by fusion. Nuclear fission involves the splitting of the nucleus of a heavy chemical element by bombardment with neutrons. Nuclear fusion involves the uniting of two nuclei of an element at high temperatures and pressure to form the nucleus of a new, heavier, element. In each process, nuclear energy is released. (page 537)

42. Chemistry EXERCISE 2 Nuclear Energy (page 537) 1. According to the information in the passage and the atomic masses shown in the periodic table, when would energy from nuclear fusion be released? (1) when uranium nuclei are fused to make plutonium (2) when hydrogen nuclei are fused to make oxygen (3) when oxygen nuclei are fused to make helium (4) when hydrogen nuclei are fused to make helium (5) when helium nuclei are fused to make hydrogen

43. Chemistry EXERCISE 2 Nuclear Energy (page 537) 2. Energy from nuclear fission would be released in the splitting of the nucleus of which element? (1) plutonium (2) hydrogen (3) oxygen (4) helium (5) carbon

44. Chemistry EXERCISE 2 Nuclear Energy (page 537) 3. Identify the following statements about nuclear power as true (T) or false (F). _________ The Three Mile Island accident contaminated a nearby forest. _________ Nuclear waste is safe to dispose of in landfills. _________ The Chernobyl accident could have been prevented. _________ Fuel rods must also have control rods to control the reaction.

45. Chemistry Nuclear Energy Radioactivity that is Useful Not all radioactivity is harmful. Particles of radioactive carbon are in the air and inhaled by animals and people every day. It is this radioactive carbon that allows paleontologists to calculate how long an organism has been dead. (page 538)

46. Chemistry Nuclear Energy Radioactivity that is Useful Radioactive carbon

47. Chemistry Nuclear Energy Radioactivity that is Useful Once the organism dies, it no longer takes in additional radioactive C14, and the amount of radioactive carbon that is present in the organism starts to decay or lose some of its radioactivity in the form of subatomic particles called alpha or beta particles. (page 538)

48. Chemistry Nuclear Energy Radioactivity that is Useful The release of alpha and beta particles would contaminate nearby objects with radioactivity. This process of radiocarbon dating has given scientists a tool to examine and date fossils from once-living organisms including early man. (page 538)

49. Chemistry Nuclear Energy Radioactivity that is Useful Smoke detectors also have a small, safe amount of material that gives off alpha particles. Some smoke detectors contain small amounts of Am241 (Americium) that releases a steady stream of alpha particles between two electrodes. When smoke particles interrupt the current between the two electrodes, an alarm sounds. (page 538)

50. Chemistry Nuclear Energy Radioactivity that is Useful Radioactive materials are also used in the treatment of some cancers. An entire branch of medicine, called nuclear medicine, researches and uses radioactive materials to treat the human body. (page 538)