Supplemental Problems. Problem Set 7.1

Transcription

1 Supplemental Problems Problem Set Compare the energies and frequencies of two photons, one with a short wavelength, the other with a long wavelength. 2. Consider the following transitions (1) n = 1 to n = 3 (2) n = 3 to n = 4 (3) n = 3 to n = 2 (4) n = 5 to n = 3 a. Which one involves the ground state? b. Which absorbs the most energy? c. Which emits the most energy? 3. According to the Bohr model, the radius of a circular orbit is given by the expression R (in nm) = n 2 Draw successive orbits for the hydrogen electron at n = 1,2,3, and 4. Indicate by arrows transitions between orbits that lead to lines in the a. Lyman series b. Balmer series c. Paschen series 4. A golf ball weighs about lb. Calculate the de Broglie wavelength of a golf ball traveling at 1.00 x 10 2 miles per hour.

2 Problem Set 7.3 Supplement Questions 1) Give the formula for each of the following: a. oxide ion b. peroxide ion c. superoxide ion d. potassium superoxide e. sodium peroxide f. barium peroxide g. hydrogen peroxide 2) What is the symbol for the element that a. completes the 5d level b. completes the 4f level 3) Write the formula for the compound(s) formed when strontium reacts with a. nitrogen b. bromine c. water d. oxygen 4) Write a balanced net ionic equation for each of the following: a. Chlorine gas is passed over magnesium ribbon. What reactant gets oxidized? b. Powdered barium peroxide is sprinkled in water. c. Lithium chunks are mixed with sulfur. d. Barium metal is dropped in water. What color would you see if phenolphthalein were dropped in the final mixture? e. Sulfur dioxide is bubbled through water. f. A piece of potassium is dropped in distilled water. What observations would you make as the reaction took place? g. Calcium oxide is dropped in distilled water.

3 5) Identify the Group 2 element(s) that a. do not give a flame test b. forms a peroxide readily c. is least metallic 6) Name and give the symbol for the element with the characteristic given below: a. Electron configuration of 1s 2 2s 2 2p 6 3s 2 3p 3 b. Lowest ionization energy in Group 7 c. Its +2 ion has the configuration [Ar] 3d 2 d. Alkali metal with the largest atomic radius e. Largest ionization energy in the third period f. Largest expected electron affinity 7) Write the electron configuration for each of the following: a. Give the electron configuration for Cr 3+ b. Give the electron configuration for Mn 2+ c. Give the electron configuration for Li + d. Give the electron configuration for Sn 4+ e. Give the electron configuration for Sn 2+ f. Give the electron configuration for S 2- Continued Next Page

4 PS 7.3 Supplements continued The code letters A to Z as well as Aa and Bb have been assigned to the elements in the periodic table. These code letters do not represent the chemical symbols, nor have the letters been assigned in alphabetical order. These letters are presented in groups, and your assignment is to arrange these elements in the proper periodic form, according to the information provided. The atomic numbers are given in the table. The best way to start is to find in which group each family belongs, and then to arrange the elements within the group. The following elements belong together in groups: NOV, HIPTU, ELRY, AGAaBb, JMZ, DSQ, CKX, BFW. The following clues are given: 1. V forms only +3 ions. O has the largest ionization energy in its group. 2. N can exist both as N + and N T reacts violently with water. 4. Elements I and H form the superoxides IO 2, and HO 2. H has a lower ionization energy than does I. 5. L is highly stable. 6. A reacts moderately with water in a single replacement reaction in order to produce a basic solution. 7. Aa gives an orange flame test, A and G give no flame test color, Bb gives a red flame test. 8. S is a yellowish-green gas. 9. The first through fourth ionization energies of G in kj/mol are: ,850 The first through fourth ionization energies of A in kj/mol are: , P is diatomic. 11. R emits blue light when used in welding has a lower ionization energy than does Y. 12. E is more reactive than R. 13. Atom Y contains 2 shielding electrons. 14. A balloon filled with gaseous element E would sink to the ground. 15. M 2- is isoelectric with E. 16. The melting point of U is smaller than that of T. 17. Elements C, F, O, and W are metalloids. 18. Both F and W are used as semiconductors in computer chips. W has a more endothermic electron affinity. 19. U forms the peroxide U 2 O B has two unpaired electrons in its 2p orbitals. 21. Z has a smaller ionization energy than does J. 22. J, although not in the same group as B, also has two unpaired electrons in its p orbitals. 23. X has three unpaired electrons and exists as a diatomic gas. 24. Z s highest energy electrons have a principal quantum number equal to K has an atomic radius larger than R but smaller than U. 26. Q has an electron affinity less exothermic than does S. 27. K has a Z eff approximately one higher than does F. 28. Q is a reddish-brown liquid. 1 2 H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K 19 Ca Ga Ge As Se Br Kr Rb Sr Follow-up Questions: 1. Of all the elements above, which is the most metallic? 2. Of the elements C, N, M, X, which element has the largest first ionization energy? 3. Of the elements C, N, M, X, which one has the largest atomic radius?

5 ONE OF THESE ESSAY QUESTIONS WILL APPEAR ON YOUR Ch. 7 TEST (all questions are taken from old AP exams) XX. The postulates of the Bohr model of the hydrogen atom can be stated as follows: (I) The electron can exist only in discrete states, each with a definite energy. (II) The electron can exist only in certain circular orbits. (III) The angular momentum of the electron is nh/2 where n is any positive integer. (IV) Radiation is emitted by the atom only when an electron makes a transition from a state of higher energy to one of lower energy. (a) State whether each of these postulates is currently considered to be correct, according to the wave mechanical description of the hydrogen atom. (b) Give the wave mechanical description that has replaced one of the postulates now considered to be incorrect. XX. First Ionization Energy (kcal/mol) Covalent Radii, Å Li Be B C N O F The covalent radii decrease regularly from Li to F, whereas the first ionization energies do not. For the ionization energies, show how currently accepted theoretical concepts can be used to explain the general trend and the two discontinuities. XX. The values of the fist three ionization energies (IE 1, IE 2, IE 3 ) for magnesium and argon are as follows: IE 1 IE 2 IE 3 (kj/mol) Mg Ar (a) Give the electronic configurations of Mg and Ar. (b) In terms of these configurations, explain why the values of the first and second ionization energies of Mg are significantly lower than the values for Ar, whereas the third ionization energy of Mg is much larger than the third ionization energy of Ar. (c) If a sample of Ar in one container and a sample of Mg in another container are each heated and chlorine is passed into each container, what compounds, if any, will be formed? Explain in terms of the electronic configurations given in part (a). (d) Element Q has the following first three ionization energies: IE 1 IE 2 IE 3 (kj/mol) Q What is the formula for the most likely compound of element Q with chlorine? Explain the choice of formula on the basis of the ionization energies. XX. The emission spectrum of hydrogen consists of several series of sharp emission lines in the ultraviolet (Lyman series), in the visible (Balmer series), and in the infrared (Paschen series, Brackett series, etc.) regions of the spectrum. (a) What feature of the electronic energies of the hydrogen atom explains why the emission spectrum consists of discrete wavelengths rather than a continuum of wavelengths? (b) Account for the existence of several series of lines in the spectrum. What quantity distinguishes one series of lines from another? (c) Draw an electronic energy level diagram for the hydrogen atom and indicate on it the transition corresponding to the line of lowest frequency in the Balmer series. (d) What is the difference between an emission spectrum and an absorption spectrum? Explain why the absorption spectrum of atomic hydrogen at room temperature has only the lines of the Lyman series.