2/15/2013. Chapter 6 6.1

Transcription

1 Chapter 6 In a self-service store, the products are grouped according to similar characteristics. With a logical classification system, finding and comparing products is easy. You will learn how elements are arranged in the periodic table and what that arrangement reveals about the elements. 1

2 Searching For an Organizing Principle How did chemists begin to organize the known elements? Chemists used the properties of elements to sort them into groups. Chlorine, bromine, and iodine have very similar chemical properties. 2

3 Mendeleev s Periodic Table How did Mendeleev organize his periodic table? Mendeleev organized elements into a periodic table. This table arranged elements into groups based on a set of repeating properties and according to increasing atomic mass. He used the periodic table to predict the properties of undiscovered elements. An Early Version of Mendeleev s Periodic Table 3

4 The Periodic Law How is the modern periodic table organized? In the modern periodic table, elements are arranged in order of increasing atomic number. The periodic law: When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. The properties of the elements within a period change as you move across a period from left to right. The pattern of properties within a period repeats as you move from one period to the next. 4

5 Metals, Nonmetals, and Metalloids What are three broad classes of elements? Three classes of elements are metals, nonmetals, and metalloids. Metals, Metalloids, and Nonmetals in the Periodic Table 5

6 Metals, Metalloids, and Nonmetals in the Periodic Table Metals Metals are good conductors of heat and electric current. 80% of elements are metals. All metals are solids at room temperature except mercury, which is a liquid. Metals have a high luster, are ductile, and are malleable. 6

7 Uses of Iron, Copper, and Aluminum Uses of Iron, Copper, and Aluminum 7

8 Uses of Iron, Copper, and Aluminum Metals, Metalloids, and Nonmetals in the Periodic Table 8

9 Nonmetals In general, nonmetals are poor conductors of heat and electric current. Most nonmetals are gases at room temperature. A few nonmetals are solids, such as sulfur and phosphorus. One nonmetal, bromine, is a dark-red liquid. 9

10 Metals, Metalloids, and Nonmetals in the Periodic Table Metalloids A metalloid generally has properties that are similar to those of metals and nonmetals. The behavior of a metalloid can be controlled by changing conditions. Metalloids are also known as semi-metals. 10

11 If a small amount of boron is mixed with silicon, the mixture is a good conductor of electric current. Silicon can be cut into wafers, and used to make computer chips. Across a period, the properties of elements become less metallic and more nonmetallic. Down a group, the properties of elements become more metallic and less nonmetallic. 11

12 6.2 A coin may contain much information in a small space its value, the year it was minted, and its country of origin. Each square in a periodic table also contains information. You will learn what types of information are usually listed in a periodic table. 6.2 Squares in the Periodic Table What type of information can be displayed in a periodic table? The periodic table displays the symbols and names of the elements, along with information about the structure of their atoms. 12

13 6.2 Some element families have names: The Group 1 elements are called alkali metals. The Group 2 elements are called alkaline earth metals. The nonmetals of Group 17 are called halogens. The nonmetal gases of group 18 are called noble gases. 13

14 Electron Configurations in Groups How can elements be classified based on their electron configurations? Elements can be sorted into groups based on their electron configurations. Elements in the same family have the same outer electron configuration = valence electrons. 14

15 6.2 The Noble Gases The noble gases are the elements in Group 18 of the periodic table; all noble gases except helium have 8 valence electrons. Helium (He) 2 Neon (Ne) 2-8 Argon (Ar) Krypton (Kr) The blimp contains helium, one of the noble gases. 15

16 6.2 The alkali metals. In atoms of the Group 1 elements below, there is only one electron in the highest occupied energy level; one valence electron. Lithium (Li) 2-1 Sodium (Na) Potassium (K) The carbon family In atoms of the Group 14 elements below, there are four valence electrons. Carbon (C) 2-4 Silicon (Si) Germanium (Ge)

17

18

19 6.2 Transition Elements There are two types of transition elements transition metals and inner transition metals. They are classified based on their electron configurations. 6.2 In atoms of a transition metal, the d sublevel is filling with electrons. In atoms of an inner transition metal, the f sublevel is filling with electrons. 19

20 6.2 Blocks of Elements The Elements: Forged in Stars - YouTube 20

21 In the Earth s Crust: Oxygen Silicon Aluminum Iron Calcium Sodium Potassium Magnesium Titanium Hydrogen Dissolved in the Oceans: Chlorine Sodium Magnesium Sulfur Calcium Potassium Bromine Carbon Strontium Boron 21

22 In the Atmosphere: Nitrogen Oxygen Argon Neon Helium Krypton Hydrogen Xenon Radon In the Sun: Hydrogen Helium Oxygen Carbon Nitrogen Silicon Magnesium Neon Iron Sulfur 22

23 In your body: Oxygen Carbon Hydrogen Nitrogen Calcium Phosphorus Sulfur Potassium Sodium Chlorine Soft, silver-grey metals. Low melting and boiling points. Electron configuration ends in s 1. Most reactive: not found uncombined in nature. Obtained in the pure form by electrolysis of their fused salts. Potassium Video - The Periodic Table of Videos - University of Nottingham 23

24 Relatively soft, but harder than alkali metals. Although not as reactive as alkali metals, still very reactive and not found in nature in the elemental state. Electron configuration ends in s 2. Obtained in the pure form through electrolysis of their fused salts. Densities, melting and boiling points are higher than respective alkali metals. Radium Video - The Periodic Table of Videos - University of Nottingham Most are ductile, malleable and good conductors of heat and electricity. Compounds of transition metals tend to have color. d sublevel is filling. Obtained from mineral deposits in the earth s crust. Precious metals are used for currency among other things. Darmstadtium Video - The Periodic Table of Videos - University of Nottingham 24

25 Nonmetals. Very reactive; not found in nature uncombined. Electron configuration ends in s 2 p 5. Obtained from the electrolysis of their fused salts. Commercial applications include antibacterial properties. Chlorine Video - The Periodic Table of Videos - University of Nottingham Non-reactive (inert) gases. Electron configuration ends in s 2 p 6 (except He is just s 2 ). Rarely form compounds; can combine with fluorine. Commercial applications include colored signs lit up as discharge tubes. Incandescent light bulbs are filled with argon. Radon Video - The Periodic Table of Videos - University of Nottingham 25

26 Sodium chloride (table salt) produced the geometric pattern in the photograph. Such a pattern can be used to calculate the position of nuclei in a solid. You will learn how properties such as atomic size are related to the location of elements in the periodic table. Trends in Atomic Size What are the trends among the elements for atomic size? The atomic radius is one half of the distance between the nuclei of two atoms of the same element when the atoms are joined. 26

27 Group and Periodic Trends in Atomic Size In general, atomic size increases from top to bottom within a group and decreases from left to right across a period. Down a group, atomic size increases due to additional energy levels. Across a period atomic size decreases due to increasing nuclear charge. This graph plots atomic radius versus atomic number for 55 elements. INTERPRETING GRAPHS a. Analyzing Data Which alkali metal has an atomic radius of 238 pm? b. Drawing Conclusions Based on the data for alkali metals and noble gases, how does atomic size change within a group? c. Predicting Is an atom of barium, atomic number 56, smaller or larger than an atom of cesium (Cs)? 27

28 Ions How do ions form? 28

29 Positive ions form when an atom loses electron(s). Negative ions form when an atom gains electron(s). 29

30 Some compounds are composed of particles called ions. An ion is an atom or group of atoms that has a positive or negative charge. A cation is an ion with a positive charge. An anion is an ion with a negative charge. Trends in Ionization Energy What are the trends among the elements for first ionization energy, ionic size, and electronegativity? The energy required to remove an electron from an atom is called ionization energy. The energy required to remove the first electron from an atom is called the first ionization energy. The energy required to remove a second electron is called the second ionization energy. 30

31 Group and Periodic Trends in Ionization Energy First ionization energy tends to decrease from top to bottom within a group and increase from left to right across a period. Down a group increasing levels of electrons shield the effect of the nucleus therefore reducing energy needed to remove an outer electron. Across a period there in no increase in energy levels, and increasing nuclear charge makes it more difficult to remove an outer electron. 31

32 Trends in Ionic Size During reactions between metals and nonmetals, metal atoms tend to lose electrons, and nonmetal atoms tend to gain electrons. The transfer has a predictable effect on the size of the ions that form. Cations are always smaller than the atoms from which they form. Anions are always larger than the atoms from which they form. 32

33 Relative Sizes of Some Atoms and Ions Trends in Ionic Size Size generally increases 33

34 Trends in Electronegativity Electronegativity is the ability of an atom to attract electrons to itself when it is in involved in a bond. In general, electronegativity values decrease from top to bottom within a group, and increase from left to right across a period. Electronegativity decreases down a group because of increasing atomic size and the shielding effect of inner level electrons. Electronegativity increases across a period because of decreasing atomic size and increasing nuclear charge. Summary of Trends What is the underlying cause of periodic trends? Periodic trends can be explained by variations in atomic structure, nuclear charge, and shielding effect. 34