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CHEM 141 Answers

Answers for Exam 2

QuestionAnswer
Some wavelengths can melt solids such as solid Xe. What is true about this process? Energy from the light is absorbed by the system.
The mass of a proton is 1.67x10^-27kg, what's the wavelength of a proton traveling at a velocity of 5.1x10^6 m/s? 7.8x10^-14
The emission spectrum for one element has 4 distinct bands of color between 400nm and 700nm. A second emission spectrum has 6 distinct bands of color between 400nm and 700nm. What can you say about the elements that generated these 2 emission spectra? The spectra are generated from different elements.
A photon of red light has a wavelength of 700nm, what can you say about the wavelength of a photon of yellow light? The photon of yellow light has a wavelength that is less than 700nm.
Coulomb's Law can be used to model the attractive or repulsive electrostatic force. Consider the force that exists between a valence electron and the nucleus of an atom. How does this force change when moving down a group (column) on the periodic table? The force decreases because the effective nuclear charge stays constant while the distance between the electron and the nucleus increases.
What causes lines to appear on an emission spectrum? The atom emits a photon when an electron moves from a higher energy level to a lower energy level.
Mg has a smaller atomic radius than Na, why? Mg has a higher effective nuclear charge than NA so the valence electrons feel a stronger attraction to the nucleus.
An electron moves from the n=1energy level to the n=3 energy level, what is the role of the photon in this process? A photon is absorbed.
If the wavelength of visible light is decreased, what changes? The frequency of the light and the energy of the light.
How many elements across is the d-block of the periodic table and why? 10 elements across because there are 5 d-orbitals in a subshell which can hold 2 electrons each.
Why was the Bohr model of the atom an improvement over Rutherford's model? The Bohr model can explain absorption and emission in the H atom, whereas Rutherford's model cannot.
Consider the imaginary element Z. Do you expect Z or Z- to have a larger radius and why? Z- because it has more electrons than Z so the electron-electron repulsions push the electron cloud farther from the nucleus.
2 waves of light, A and B have the same speed. Wave A has a wavelength of 730nm and wave B has a wavelength of 515nm. What can you say about the frequency? A has a lower frequency than wave B.
2 imaginary elements, X and Y, are in the same column on the periodic table. Y has a higher atomic number. Which has the lower ionization energy? Y because the valence electrons are farther from the nucleus but experience the same effective nuclear charge.
Ionization energies for an imaginary element: 1st IE= 1,100k J/mol, 2nd IE= 1,950 kJ/mol, 3rd IE= 2,890 kJ/mol, 4th IE= 7,740 kJ/mol, 5th IE= 9.120 kJ/mol, and 6th IE 10,050 kJ/mol. Why is there such a large number between the 3rd and 4th IE? The 4th electron removed is a core electron. Core electrons experience a higher effective nuclear charge and are closer to the nucleus than valence electrons.
Spectra are direct evidence for the existence of quantized energy levels in an atom. What would an emission spectrum look like if quantized energy levels in an atom did not exist? A continuous visible spectrum (a complete rainbow).
An element has 17 electrons. In the ground state, how many core and valence electrons does it have? 10 core, 7 valence.
Which of the following elements has its highest energy electron in a P-orbital (dumbbell shape)? (out of Na, Ca, C and Fe) C
When a beam of light hits a barricade containing two small slits, what happens and why? The waves of light go through the slits and hit a screen, producing a pattern of bright and dark lines. When diffracted light overlaps out-of-phase, the light appears dimmer. When diffracted light overlaps in-phase, the light appears brighter.
Do you predict Ar or K+ to have a smaller radius? Why? K+ is smaller than Ar because the potassium ion's 19 protons exert a stronger force than argon's 18 protons on the same number of electrons.
Why must we consider the wave-like properties of an electron but not a larger object (such as a tennis ball)? The wavelength of an electron is similar in size to the atom and therefore affects the properties of the electron.
What is the wavelength of a photon of light that has an energy of 4.24 x 10-18 J? 46.9 nm
What statement is true about a p-orbital? An electron in a p-orbital is likely to be found in a dumbbell shaped region of space around the nucleus.
Created by: CRO009
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