Page 59 - Chemistry eBook

Part B–2
Answer all questions in this part.
The bright-line spectra for three elements and a mixture of elements are shown below.
Bright-Line Spectra
Directions (51–65): Record your answers in the spaces provided in your answer booklet. Some questions
lithium 51 Explain, in terms of protons and neutrons, why U-235 and U-238 are different isotopes cadmium
may require the use of the Reference Tables for Physical Setting/Chemistry.
of uranium. [1]
Base your answers to questions 52 through 54 on the information below.
The bright-line spectra for three elements and a mixture of elements are shown below.
Bright-Line Spectra
lithium cadmium strontium mixture
52 Explain, in terms of both electrons and energy, how the bright-line spectrum of an element is produced. [1]
53 Identify all the elements in the mixture. [1]
54 State the total number of valence electrons in a cadmium atom in the ground state. [1]
750 700
650 600 550 500 450 400 Wavelength (nm)
element is produced. [1]
53 Identify all the elements in the mixture. [1]
54 State the total number of valence electrons in a cadmium atom in the ground state. [1]
[8]
Sample Regents Questions
Jan 2011 #52-54
P.S./Chem.–June ’11
strontium mixture
750 700 650
600 550 500 450 400 Wavelength (nm)
52 Explain, in terms of both electrons and energy, how the bright-line spectrum of an
Answer
P.S./Chem.–June ’11 [8]
52) Answer: When electrons change from an excited state to a ground state, they let out energy that produces bright line spectra.
53) Answer: Lithium and strontium
Explanation: Follow the lines down from each element to see if it’s included in the mixture. The lines from lithium and strontium match the mixture’s lines. The lines from cadmium are not shown in the mixture. Therefore, we know that cadmium is not part of the mixture.
54) Answer: 2
Explanation: Look up the electron configuration of cadmium (Ca) in Reffy (p. 9). We see that there are 2 electrons on the last shell (the valence shell).
(Since the electron can’t have more than 8 electrons on its last shell, it has to make 2 electrons jump to the next shell.)
UNIT 2: ATOMIC STRUCTURE © 59