CHAPTER 19 Elements and their Properties

Transcription

1 CHAPTER 19 Elements and their Properties

2 Elements and their Properties PSc.2.1 Understand types, properties, and structure of matter. PSc Classify matter as: homogeneous or heterogeneous; pure substance or mixture; element or compound; metals, nonmetals, or metalloids; solution, colloid, or suspension. PSc Explain the phases of matter and the physical changes that matter undergo. PSc Compare physical and chemical properties of various types of matter. PSc Interpret data presented in Bohr model diagrams and dot diagrams for atom and ions of elements 1 through 18.

3 Elements and their Properties PSc.2.2 Understand chemical bonding and chemical interactions. PSc Infer valence electrons, oxidation number, and reactivity of an element based on its location in the Periodic Table. PSc Infer the type of chemical bond that occurs, whether covalent, ionic, or metallic, in a given substance. PSc Predict chemical formulas and names for simple compounds based on knowledge of bond formation and naming conventions. PSc Exemplify the laws of conservation of mass by balancing chemical equations. PSc Classify types of reactions such as synthesis, decomposition, single replacement or double replacement. PSc Summarize the characteristics and interactions of acids and bases. PSc.2.3 Understand the role of the nucleus in radiation and radioactivity. PSc Compare nuclear reactions including alpha decay, beta decay, and gamma decay: nuclear fusion and nuclear fission PSc2.3.2 Exemplify the radioactive decay of unstable nuclei using the concept of halflife.

4 Read Chapter 19; pages: Elements and their Properties Objectives: - Describe the properties of a typical metal; Identify the alkali metals and alkaline earth metals; Differentiate among three groups of transition elements; Recognize hydrogen as a nonmetal; Compare and contrast properties of the halogens; Describe properties and uses of the noble gases; Distinguish among metals, nonmetals, and metalloids; Describe the nature of allotropes; Recognize the significance of differences in crystal structure in carbon; Understand the importance of synthetic elements; Vocabulary: Allotrope Diatomic molecule Ductile Malleable Metal Metallic bonding Metalloid Nonmetal Radioactive element Salt Semiconductor Sublimation Transition element Transuranium element Noble gases

5 Metals

6 Blue: metals Green: metalloids Yellow: nonmetals

7 Metals Properties of Metals Metals- good conductors of heat and electricity, All but one are solid at room temperature. Metals also reflect light (Luster) Malleable- Can be hammered or rolled into sheets. Ductile- Can be drawn into wires.

8 Metals Ionic Bonding in Metals The atoms of metals generally have one to three electrons in their outer energy levels. In chemical reactions, metals tend to give up electrons easily because of the strength of charge of the protons in the nucleus. When metals combine with nonmetals, the atoms of the metals tend to lose electrons to the atoms of nonmetals, forming ionic bonds. Both metals and nonmetals become more chemically stable when they form ions.

9 Metals Metallic Bonding In metallic bonding, positively charged metallic ions are surrounded by a cloud of electrons. Outer-level electrons are not held tightly to the nucleus of an atom. Rather, the electrons move freely among many positively charged ions. As seen, the electrons form a cloud around the ions of the metal.

10 Metals Metallic Bonding The idea of metallic bonding explains many properties of metals, for example: When a metal is hammered into a sheet or drawn into a wire, it does not break because the ions are in layers that slide past one another without losing their attraction to the electron cloud. Metals are good conductors because the outer-level electrons are weakly held.

11 Metals The Alkali Metals Elements in group 1 are the alkali metals. These metals are shiny, malleable, and ductile. They are also good conductors of heat and electricity. They are softer than most other metals. They react rapidly, sometimes violently with oxygen and water.

12 Metals The Alkali Metals Alkali metals don t occur in nature in their elemental form but are stored in substances that are unreactive, such as an oil. Each atom of an alkali metal has one electron in its outer energy level. This electron is given up when an alkali metal combines with another atom. As a result, the alkali metal becomes a positively charged ion in a compound such as sodium chloride, NaCl or potassium bromide, KBr.

13 Metals The Alkali Metals Alkali metals and their compounds have many uses, such as the need for potassium and sodium compounds to stay healthy. Doctors sometimes use lithium compounds to treat bipolar depression. The operation of photocells depends on rubidium or cesium compounds.

14 Metals The Alkali Metals Francium, the last element in Group 1, is extremely rare and radioactive. A radioactive element is one in which the nucleus breaks down and gives off particles and energy. Francium can be found in uranium minerals but only 25g to 30g of francium are in all of Earth s crust at one time.

15 Metals The Alkaline Earth Metals Group 2 Alkaline earth metal- Not as reactive as Alkali Metals. Like most metals, theses metals are shiny, malleable, and ductile. They also combine readily with other elements that are not found as free elements in nature.

16 Metals The Alkaline Earth Metals Each atom of an alkaline earth metal has two electrons in tis outer energy level. These electrons are given up when an alkaline earth metal combines with a nonmetal. As a result, the alkaline earth metal becomes a positively charged ion in a compound such as calcium fluoride, CaF 2.

17 Metals Fireworks and Other Uses Magnesium- used to produce the brilliant white color in fireworks. Compounds of strontium produce the bright red flashes.

18 Metals Fireworks and Other Uses Magnesium s lightness and strength account for its use in cars, planes, and spacecraft. Magnesium also is used in compounds to make such things as household ladders, and baseball and softball bats. Most life on Earth depends upon chlorophyll, a magnesium compound that enables plants to make food.

19 Metals The Alkaline Earth Metals and Your Body Marble statues and some countertops are made of the calcium compound calcium carbonate. Calcium is seldom used as a free metal, but its compounds are needed for life. Calcium phosphate in your bones helps make them strong.

20 Metals The Alkaline Earth Metals and Your Body The barium compound BaSO 4 is used to diagnose some digestive disorders because it absorbs X-ray radiation well. Radium, the last element in Group 2, is radioactive and is found associated with uranium. It was once used to treat cancers.

21 Metals Transition Elements Transition elements are those elements in Groups 3 through 12 in the periodic table. (Transition between the other groups)

22 Metals Transition Elements They are called transition elements because they are considered to be elements in transition between Groups 1 and 2 and Groups 13 through 18. Transition elements are familiar because they often occur in nature as uncombined elements, unlike Group 1 and Group 2 metals which are less stable.

23 Metals Transition Elements Transition elements often form colored compounds. Gems show brightly colored compounds containing chromium. Cadmium yellow and cobalt blue paints are made from compounds of transition elements. However, cadmium and cobalt paints are so toxic, so their use is limited.

24 Metals Iron, Cobalt, and Nickel First element in Groups 8, 9, and 10 are iron, cobalt, and nickel, which form a unique cluster of transition elements. These three sometimes called the iron triad. All three elements are used in the process to create steel and other metal mixtures.

25 Metals Iron, Cobalt, and Nickel Iron the main component of steel is the most widely used of all metals. It is the second most abundant metallic element in Earth s crust after aluminum. Other metals like cobalt and nickel are often added to steel. Nickel is added to some metals to give them strength.

26 Metals Copper, Silver, and Gold The three elements in Group 11 are copper, silver, and gold referred to as the coinage metals. Because they are so stable and malleable and can be found as free elements in nature, these metals were once used widely to make coins. Because they are so expensive, the use of gold in coins was stopped in 1933, and the use of silver in coins was stopped in Most coins now are made of nickel and copper.

27 Metals Copper, Silver, and Gold Copper often is used in electrical wiring because of its superior ability to conduct electricity and its relatively low cost. Silver iodide and silver bromide break down when exposed to light, producing an image on paper. Consequently, these compounds are used to make photographic film and paper. Silver and gold are used in jewelry because of their attractive color, relative softness, resistance to corrosion and rarity.

28 Metals Zinc, Cadmium, and Mercury Zinc, cadmium, and mercury are found in Group 12 of the periodic table. Zinc combines with oxygen in the air to form a thin, protective coating of zinc oxide on its surface. Zinc and cadmium often are used to coat, or plate, other metals such as iron because of this protective quality. Cadmium is used also in rechargeable batteries.

29 Metals Zinc, Cadmium, and Mercury Mercury is a silvery, liquid metal the only metal that is a liquid at room temperature. It is used in thermometers, thermostats, switches, and batteries. Mercury is poisonous and can accumulate in the body. People have died of mercury poisoning after eating fish that lived in mercury-contaminated water.

30 Metals The Inner Transition Metals Inner transition elements- Elements that are disconnected from the periodic table To save space, the periodic table usually isn t shown with the inner transition elements.

31 Metals The Inner Transition Metals They are called inner Transition metals because like the transition elements, they fit in the periodic table between Groups 3 and 4, and in periods 6 and 7; most often to save room, they are listed below the table. Lanthanide- Upper row of inner transition elements

32 Metals The Lanthanides The first row includes a series of elements with atomic numbers of are called the lanthanide series because they follow the element lanthanum. Lanthanum, cerium, praseodymium and samarium are used with carbon to make a compound that is used extensively by the motion picture industry. Europium, gadolinium, and terbium are used to produce the colors we see on our television screens.

33 Metals The Actinides The second row of inner transition metals includes elements with atomic numbers ranging from These elements are called the actinide series because they follow the element actinium. ALL of the actinides are radioactive and unstable. Their unstable nature makes researching them difficult. Thorium and uranium are actinides found in Earth s crust in usable quantities. Thorium is used in making the glass for high quality camera lenses because it bends light without much distortion.

34 Metals The Actinides Uranium, best known for its use in nuclear reactors and in weapons applications, and one of its compounds has best been used as photograph toner. Metals in the Crust The Earth s crust contains many compounds and a few uncombined metals such as gold and copper. Metals must be mined and separated from their ores.

35 Metals Ores: Minerals and Mixtures Metals in Earth s crust that combined with other elements are found as ores. Most ores consist of a metal compound, or mineral, within a mixture of clay or rock. After an ore is mined, the rock is separated from the mineral; then the mineral is often heated in a process called roasting; and finally, the metal is refined into a pure form. Removing the waste rock can be expensive and if the cost of removal is greater than the value of the desired material, the mineral no longer is classified as an ore.

36 Nonmetals

37 Nonmetals Properties of Nonmetals Most of your body s mass is made of oxygen, carbon, hydrogen, and nitrogen. Calcium, a metal, and other elements make up the remaining four percent of your body s mass. In the periodic table, all nonmetals except hydrogen are found at the right of the stair-step line.

38 Nonmetals Properties of Nonmetals Phosphorus, sulfur, and chlorine are among these other elements found in your body. These elements are classified a nonmetals. Nonmetals are elements that usually are gases or brittle solids at room temperature. Because solid nonmetals are brittle or powdery, they are not malleable or ductile. Most nonmetals do not conduct heat or electricity well, and generally not shiny.

39 Nonmetals Bonding in Nonmetals The electrons in most nonmetals are strongly attracted to the nucleus of the atom. So, as a group, nonmetals are poor conductors of heat and electricity. Most nonmetals can form ionic and covalent compounds, examples: lead and sulfur bond ionically to form lead sulfide, PbS, known as galena And carbon and oxygen can bond covalently to form carbon dioxide, CO 2

40 Nonmetals Bonding in Nonmetals When nonmetals gain electrons from metals, the nonmetals become negative ions in ionic compounds, an example is potassium iodide, KI, which is often added to table salt and is formed from the nonmetal iodine and the metal potassium. When bonded with other nonmetals, atoms of nonmetals usually share electrons to form covalent compounds, of which is ammonia, NH 3, which is a compound of nitrogen and hydrogen.

41 Nonmetals Hydrogen 90% of all of the atoms in the universe is hydrogen Most hydrogen on Earth is found in the compound water; when water is broken down into elements, hydrogen becomes a gas made up of diatomic molecules, H 2. A diatomic molecule consists of two atoms of the same element in a covalent bond. Hydrogen is highly reactive.

42 Nonmetals Hydrogen A hydrogen atom has a single electron, which the atom shares when it combines with other nonmetals. For example, hydrogen burns in oxygen to form water H 2 O, in which hydrogen shares electrons with oxygen. Hydrogen can gain an electron when it combines with alkali and alkaline earth metals. The compounds formed are hydrides, such as sodium hydride, NaH.

43 Nonmetals The Halogens Group 17 is called halogens: fluorine, chlorine, bromine, iodine, and astatine. These are very reactive in their elemental form. The halogens compounds have many uses: Fluorides are added to toothpaste and to city water systems to prevent tooth decay Chlorine compounds are used in pools to disinfect the water

44 Nonmetals The Halogens Because an atom of a halogen has seven electrons in its outer energy level, only one electron is needed to complete this energy level. If a halogen gains an electron from a metal, an ionic compound called a salt is formed: The definition of salt is - when a halogen gains an electron from a metal.

45 Nonmetals The Halogens In the gaseous state, the halogens form reactive diatomic covalent molecules and can be identified by their distinctive colors: chlorine has a greenish yellow color, bromine has a reddish orange color, and iodine has a violet color

46 Nonmetals The Halogens Fluorine is the most chemically active of all elements. Hydrofluoric acid, a mixture of hydrogen fluoride and water, is used to etch glass and to frost the inner surfaces of lightbulbs and it is used in the fabrication of semiconductors.

47 Nonmetals Uses of Halogens Household and industrial bleaches used to whiten flour, clothing, and paper also contain chlorine compounds. Chlorine, the most abundant halogen, is obtained from seawater at ocean-salt recovery sites. Bromine, only nonmetal that is a liquid at room temperature, extracted from compounds in seawater. Bromine compounds are used as dyes in cosmetics.

48 Nonmetals Uses of Halogens Iodine, a shiny purple-gray solid at room temp. and is also obtained from seawater; when heated, iodine changes directly to a purple vapor. The process of a solid changing directly to a vapor without forming a liquid is called sublimation. Iodine is essential in you diet for the production of the hormone thyroxin and to prevent goiter. Astatine is the last member of Group 17. It is radioactive and rare, but has many properties similar to those of the other halogens. But due to its rarity, there is no known use.

49 Nonmetals The Noble Gases Group 18 Noble Gases they are stable because their outermost energy levels are full. No naturally occurring noble gas compounds are known, but several compounds of xenon and krypton with fluorine have been created in the lab. The stability of noble gasses is what makes them useful. In addition, the light weight of helium makes it useful in lighter-than-air blimps and balloons.

50 Nonmetals The Noble Gases Neon and argon are used in neon lights for advertising. Argon and krypton are also used in electric lightbulbs to produce light lasers.

51 Mixed Groups Properties of Metalloids Metalloids share unusual characteristics. Metalloids can form ionic and covalent bonds with other elements and can have metallic and nonmetallic properties. Some metalloids are semiconductors- conduct electricity better than most nonmetals, but not as well as some metals, giving them the name of semiconductors.

52 Mixed Groups Properties of Metalloids With the exception of aluminum, the metalloids are the elements in the periodic table that are located along the stair-step line. The mixed groups 13, 14, 15, 16, and 17 contain metals, nonmetals, and metalloids.

53 Mixed Groups The Boron Group Boron, a metalloid, is the first element in Group 13. If you look around your home, you might find two compounds of boron.

54 Mixed Groups The Boron Group One of these is borax, which is used in some laundry products to soften water. The other is boric acid, a mild antiseptic. Boron also is used as a grinding material and as boranes, which are compounds used for jet and rocket fuel.

55 Mixed Groups The Boron Group Aluminum- is the MOST abundant metal in Earth s crust. It is used in soft-drink cans, foil wrap, cooking pans, and as siding. Aluminum is strong and light and is used in the construction of airplanes.

56 Mixed Groups The Carbon Group Each element in Group 14, the carbon family, has four electrons in its outer energy level, but this is where much of the similarity ends. Carbon is a nonmetal, silicon and germanium are metalloids, and tin and lead are metals.

57 Mixed Groups The Carbon Group Carbon occurs as an element in coal and as a compound in oil, natural gas, and foods. Carbon in these materials can combine with oxygen to produce carbon dioxide, CO 2. As you know, via photosynthesis, plants turn CO 2 into food and produce oxygen essential our for life. All organic compounds contain carbon, but not all carbon compounds are organic.

58 Mixed Groups The Carbon Group Silicon is second only to oxygen in abundance in Earth s crust. Most silicon, SiO 2 is found in sand, almost all rocks and soil. The crystal structure of silicon dioxide is similar to the structure of diamond. Silicon occurs as two allotropes which are different forms of the same element. One allotrope of silicon is a hard, gray substance, and the other is a brown powder.

59 Mixed Groups The Carbon Group Silicon is the main component in semiconductors elements that conduct an electric current under certain conditions. Germanium, the other metalloid in the carbon group, is used along with silicon in making semiconductors.

60 Mixed Groups The Carbon Group Tin is used to coat other metals to prevent corrosion. Tin also is combined with other metals to produce bronze and pewter. Lead was used widely in paint at one time, but because it is toxic, lead no longer is used.

61 Mixed Groups Allotropes of Carbon Carbon Allotropesdiamond and graphite, In a diamond, each carbon atom is bonded to four other carbon atoms at the vertices, or corner points, of a tetrahedron.

62 Mixed Groups Allotropes of Carbon In turn, many tetrahedrons join together to form a giant molecule in which the atoms are held tightly in a strong crystalline structure. This structure accounts for the hardness of diamond.

63 Mixed Groups Allotropes of Carbon Graphite is a black powder that consists of hexagonal layers of carbon atoms. In the hexagons, each carbon atom is bonded to three other carbon atoms. The fourth electron of each atom is bonded weakly to the next layer next to it.

64 Mixed Groups Allotropes of Carbon This structure allows the layers to slide easily past one another, making graphite an excellent lubricant.

65 Mixed Groups Allotropes of Carbon In the mid-1980s, a new allotrope of carbon called buckminsterfullerene was discovered. This soccer-ball-shaped molecule, informally called a buckyball, was named after the architect-engineer R. Buckminster Fuller, who designed structures with similar shapes.

66 Mixed Groups Allotropes of Carbon In 1991, scientists were able to use the buckyballs to synthesize extremely thin, graphite-like tubes. These tubes, called nanotubes are about 1 billionth of a meter in diameter. Nanotubes might be used someday to make computers that are smaller and faster, and to make strong building materials.

67 Mixed Groups The Nitrogen Group The nitrogen family makes up Group 15. Each element has five electrons in its outer energy level. These elements tend to share electrons and to form covalent compounds with other elements.

68 Mixed Groups The Nitrogen Group Nitrogen often is used to make nitrates, which are compounds that contain nitrate ion, NO 3 - and ammonia, NH 3, both are used in in making fertilizers. Nitrogen is the fourth most abundant element in your body. Each breath you take is about 80% gaseous nitrogen in the form of diatomic molecules, N 2. Yet we and animals can t use nitrogen in it diatomic form. The nitrogen must be combined into compounds, such as amino acids.

69 Mixed Groups Uses of the Nitrogen Group Phosphorus is a nonmetal that has three allotropes. Phosphorus compounds can be used for many things from water softeners to fertilizers, match heads, and even in fine china. Antimony is a metalloid, and bismuth is a metal. Both elements are used with other metals to lower their melting points. Because of this property, the metal in automatic fire-sprinkler heads contains bismuth.

70 Mixed Groups The Oxygen Group Group 16 on the periodic table is the oxygen group. Oxygen, a nonmetal, exists in the air as diatomic molecules, O 2. During electrical storms, some oxygen molecules, O 2, change into ozone molecules, O 3. Nearly all living things on Earth need both O 2 and O 3.

71 Mixed Groups The Oxygen Group Nearly all living things on Earth need oxygen for respiration, in addition, the ozone layer provides protection from the Sun s ultraviolet radiation. The second element in the oxygen group is sulfur. Sulfur is a nonmetal that exists in several allotropic forms. It exists as different-shaped crystals and as a noncrystalline solid. Sulfur combines with metals to form sulfides that are so color distinctive they are used as pigments in paints

72 Mixed Groups The Oxygen Group The nonmetal selenium and two metalloids: tellurium and polonium, are the other Group 16 elements. Selenium is the most common of these three. This element is one of several that you need in trace amounts in your diet. Many multivitamins contain selenium, but it is toxic if too much of its gets in your system.

73 Mixed Groups Synthetic Elements By smashing existing elements with particles accelerated in a heavy ion accelerator, scientists have been successful in creating elements not typically found on Earth. Except for technetium-43 and promethium- 61, each synthetic element has more than 92 protons. Bombarding uranium with neutrons can make neptunium, element 93.

74 Mixed Groups Synthetic Elements Plutonium also can be changed to americium, element 95. This element is used in home smoke detectors.

75 Mixed Groups Transuranium Elements Elements having more than 92 protons, the atomic number of uranium are called transuranium elements some are in the actinide series These elements do not belong exclusively to the metal, nonmetal, or metalloid group. All of the transuranium elements are synthetic and unstable, many disintegrate quickly.

76 Mixed Groups Why make elements? The most recently discovered elements are synthetic. By studying how the synthesized elements form and disintegrate, you can gain an understanding of the forces holding the nucleus together. Radioactive elements can be useful, for example technetium s radioactivity makes it ideal for many medical applications.

77 Mixed Groups Why make elements? Element 114, discovered 1999, appears to be much more stable than most synthetic elements of its size, lasting for 30 s. May not seem long, but it lasted 100,000 times longer than an atom of element 112. Perhaps this special combination of 114 protons and 175 neutrons allows the nucleus to hold together despite the enormous repulsion between the protons.

78 Let s REVIEW

79 Section Check Question 1 Which of these compounds is not an allotrope of carbon? A. buckminsterfullerene B. diamond C. graphite D. quartz

80 Section Check Answer The answer is D. Quartz is a mineral composed of silicon dioxide. Graphite Diamond Buckminsterfullerener

81 Section Check Question 2 If you want to use a circle graph to represent the amount of hydrogen in the universe relative to other elements, how many degrees will be used to represent hydrogen? A. 36º B. 90º Answer C. 186º D. 324º The answer is D. 90 percent of the 360º in a circle is equal to 324º.

82 Section Check Question 3 Elements having more than 92 protons are called. Answer The atomic number of uranium is 92. Elements having more than 92 protons are called transuranium elements, and are synthetic and unstable.

83 Section Check Question 1 What are common properties of metals? Answer Metals are good conductors of heat and electricity, reflect light, are malleable and ductile, and, except for Mercury, are solid at room temperature.

84 Section Check Question 2 Which of these best describes electrons in metallic bonding? A. electron acceptor B. electron cloud C. electron donor D. electrons in fixed orbits Answer The answer is B. In metallic bonding, positively charged metallic ions are surrounded by a cloud of electrons.

85 Section Check Question 3 How do alkaline earth metals differ from alkali metals? Answer Alkali metals have one electron in the outer energy level of each atom. Each atom of alkaline earth metals has two electrons in its outer energy level.

86 Section Check Question 1 Which elements exist primarily as gases or brittle solids at room temperature? A. metals B. metalloids C. nonmetals D. synthetics Answer The answer is C. Solid nonmetals are brittle or powdery and not malleable or ductile.

87 Section Check Question 2 A(n) molecule consists of two atoms of the same element in a covalent bond. A. actinide B. allotropic C. diatomic D. lanthanide Answer The answer is C. When water is broken down into its elements, hydrogen becomes a gas made up of diatomic molecules.

88 Section Check Question 3 Which of the following accounts for 90 percent of the atoms in the universe? A. carbon B. hydrogen C. nitrogen D. oxygen Answer The answer is B. Hydrogen makes up 90 percent of the atoms in the universe. On Earth, most hydrogen is found in the compound water.