Physical Science - Ch 8

PSCI 170: Physical Science I

Spring 2004

Solutions to Homework Homework and Chapter 10: Elements and the Periodic Table You need to know what has been said in the class about the periodic table. Be able to use the periodic table as a tool. Know the difference between groups or families and periods. Know which are metals and which are nonmetals by looking at the periodic table. note the differences in properties of metals versus nonmetals. Be able to recognize main group versus transition elements Know that the group number of the main group (A) elements tells you the number of electrons in the outermost shell – and these are the electrons involved with bonding. Know how the group number of the main group elements can tell you what ion will form. What are the noble gases? What is characteristic of the noble gases? Their inactivity. Other information as shown by these exercises. I will not give questions just asking you to write the names of the elements given their symbols and vice versa. Note what the atomic number will tell youThe number of protons in an atom of the element, which is equal to the number of electrons in a neutral atom of the element. Applying the Concepts: Be able to answer all of these. 1. Matter is defined as anything that d) occupies space and has mass. 2. One of the physical properties of a metal, compared to a non-metal, is that the metal is malleable. This means that you can c) pound it into a thin sheet. Hand in Question for Thought: 1. How was Mendeleev able to predict the chemical and physical properties of elements that were not yet discovered? Mendeleev arranged the elements in rows of increasing atomic weights, arranged so that elements with similar properties made vertical columns. These vertical columns contained Dobereiner’s triads of elements with similar properties. Left blank spaces if the element with the next highest atomic weight did not fit with a vertical family. These blank places suggested undiscovered elements. Mendeleev predicted that elements would be discovered to fill the gaps in his table and predicted the physical and chemical properties of the yet to be discovered elements. Mendeleev is usually given credit for developing the periodic table, probably because of his dramatic and highly publicized predictions about the unknow elements. Modern Periodic Law: Similar physical and chemical properties recur periodically when the elements are listed in the order of increasing atomic number. Hand in Questions for Thought: 5, 6 and 8 5.What two things does a chemical symbol represent? Answer: A chemical symbol identifies a specific element and represents one atom of the element. 6. What do the members of the noble gas family have in common? What are their differences? Answer: The noble gases are all chemically inert, but each has a different atomic number and a different mass. They are found in the same family, but they are all found in different periods of the periodic table. 8. What is the difference between a chemical change and a physical change? Give three examples of each. Answer: A chemical change involves a change in the identity and properties of the substance, while a physical change

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is merely a size, shape, volume, or phase change. Therefore, when there is a chemical change you are making something new, a new chemical. When there is a physical change there is no change in the chemical formula of the substance, just looks a little different. You could list a number of different chemical and physical changes. Chemical Changes: things like paper burning, gasoline burning, iron rusting, Physical Changes: things like melting, freezing, water boiling, condensing, sublimation Hand in Group B Parallel Exercises: 1,3,4,5,7,8,9. 1. Write the chemical symbols for the following chemical elements: a)Argon, Ar; b)Gold, Au; c)Neon, Ne; d)Sodium, Na; e)Calcium, Ca; f)Tin, Sn 3. Identify the number of protons, neutrons and electrons in the following isotopes: Y Z

X

Y is the mass number and equal to the number of neutrons plus protons Z is the atomic number and it is equal to the number of protons in an atom of the element (also equal to the number of electrons in a neutral atom of the element) a)

14 7

N 7 protons, 7 electrons and 7 neutrons,

7 3

b) Li 3 protons, 3 electrons and 4 neutrons; c)

35 17

Cl 17 protons, 17 electrons, 18 neutrons

d)

48 20

e)

63 29

f)

230 92

Ca 20 protons, 20 electrons, 28 neutrons

Cu 29 protons, 29 electrons, 34 neutrons U 92 protons, 92 electrons and 138 neutrons

4. Identify the period and the family in the periodic table for the following elements: Use periodic table on page 249. a) Xenon Xe is in period 5 and in family VIIIA (new way of numbering families would make this 18) b) Potassium K is in period 4 and in family IA (new way of numbering families would make this 1) c) Chromium Cr is in period 4 and in family VIB (new way of numbering families would make this 6) d) Argon Ar is in period 3 and in family VIIIA (new way of numbering families would make this 18) e) Bromine Br is in period 4 and in family VIIA (new way of numbering families would make this 17) f) Barium, Ba is in period 6 and in family IIA (new way of numbering families would make this 2) 5.How many outer shell electrons are found in an atom of: Remember from class that for the main group elements (those with A in the numbering) the roman numeral tells you the number of outer shell electrons found in a neutral atom of the element. a) Na Sodium is in group IA so it has one outer shell electron. 1s22s22p63s1 b) P Phosphorus is in group VA so it has five outer shell electrons. 1s22s22p63s23p3 c) Br Bromine is in group VIIA so it has seven outer shell electrons. 1s22s22p63s23p64s23d104p5 d) I Iodine is in group VIIA so it has seven outer shell electrons. 1s22s22p63s23p64s23d104p65s24d105p5 e) Te Tellurium is in group VIA so it has six outer shell electrons. 1s22s22p63s23p64s23d104p65s24d105p4 f) Sr Strontium is in group IIA so it has two outer shell electrons. 1s22s22p63s23p64s23d104p65s2 7.Identify the charge on the following ions: Remember that you can use the information on the periodic table to identify the charges on ions too. Remember, if metals ionize they form cations (+ charged ions) and if nonmetals ionize they form anions (- charged ions). Then, remember that in nature there is the magic number of 8 electrons in the outer shell that seems to be most stable. So if the element has fewer than 4 outer shell electrons it will give up those electrons and become a cation – leaving the next shell with 8. If the

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element has greater than 4 outer shell electrons it will gain more electrons to result in 8 electrons in its outer shell and therefore become an anion. a) Aluminum Al is in group IIIA, so it will give up its three outer shell electrons and become Al3+ b) Chlorine Cl is in group VIIA, so it will gain one more electron to make 8 in its outer shell and become Cl-c) Magnesium Mg is in group IIA, so it will give up its two outer shell electrons and become Mg2+ d) Sodium Na is in group IA, so it will give up its one outer shell electron and become Na+ e) Sulfur S is in group VIA, so it will gain to more electrons to make 8 in its outer shell and become S2f) Hydrogen H is so small, it only has one electron so only one outer shell electron, which it will give up. So usually forms H+. 8. Use the periodic table to identify if the following are metals, nonmetals or semiconductors (also called metalloids and semimetals) Remember that the metals are on the left side of the periodic table and the nonmetals are on the right. The boundary in between contains the semiconductors. On page 248 of your text the metals are in blue, the nonmetals are in green and the semiconductors are in yellow. The noble gases, while they are shown in white because they are special being so stable, are also considered nonmetals. a) Radon Rn is a nonmetal b) Francium Fr is a metal c) Arsenic As is a semiconductor or semimetal or metalloid d) Phosphorus P is a nonmetal e) Hafnium Hf is a metal f) Uranium U is a metal. The inner transition elements - are also metals 9. From their charges, predict the periodic table family number for the following ions: a) F-1 (usually written F-) VIIA (or 17) b) Li+1 (usually written Li+) IA (or 1) c) B+3 (usually written B3+) IIIA (or 13) d) O-2 (usually written O2-) VIA (or 16) e) Be+2 (usually written Be2+) IIA (or 2) f) Si+4 (usually written Si4+ ) IVA (or 14)

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