vaporized sample (1) is converted to positive ions (2). Ions are accelerated (3) and deflected, according to their mass, by an electromagnet (4). Only samples with a precisely selected mass will be deflected appropriately all the way through to the detector (5). Electromagnet can be adjusted to select for different masses. After testing for a range of specific masses, their percent abundances are determined. The most abundant isotope is assigned a value of 100, and the rest are assigned a percentage amount of that, depending on how many were detected at step 5.
- What specific piece of a mass spectrometer is adjusted in order to detect particles with varying masses?
electromagnet at step 4, the deflection step
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Of the following particles, 16O+,15O+, 16O2+, (16O –16O)+ which experiences the greatest amount of deflection in a mass spectrometer? Why are all ions formed in a mass spectrometer positively charged?
the particle that experiences the most deflection is the one with the lowest m/z (mass/charge ratio), which in this group is 16O2+ (m/z of 8). Ions in a mass spectrometer are positively charged because the particles are stripped of electrons in the ionization step
- The following graph is produced when a pure sample of boron is passed through a mass spectrometer. Use the data to calculate the relative atomic mass for boron.
100 + 24.65 = 124.65
10B = (24.65/124.65) x 100 = 19.78%
11B = (100/124.65) x 100 = 80.22%
(10 x 0.1978) + (11 x 0.8022) = 10.80
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Lithium occurs naturally as two isotopes, 6Li and 7Li. The relative atomic mass of lithium is 6.941 g/mol. Determine the percent abundance of each of lithium’s isotopes.
6x + 7(1-x) = 6.941
6x +7 - 7x = 6.941
7 - 1x = 6.941 5.9% 6Li and 94.1% 7Li
-1x = -0.059
x = 0.059 or 5.9% 6Li
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State the name and the mass number of the isotope relative to which all atomic masses are measured. 12C
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Write the symbol for the species with 17 protons, 19 neutrons, and 18 electrons.
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Write the symbol for the species with 6 protons, 8 neutrons, and 6 electrons.
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Write the symbol for the species with 3 protons, 3 neutrons, and 2 electrons.
- Explain why most atomic masses are not whole numbers.
Atomic masses from the periodic table represent weighted averages of all of an element’s isotopes. This number is usually a decimal
- In the context of electromagnetic radiation, what is wavelength? How does wavelength relate to energy?
wavelength is the distance between two successive crests on a wave (or any two repeating points). The longer the wavelength, the lower the energy in the wave
- In the context of electromagnetic radiation, what is frequency? How does frequency relate to energy?
frequency is the number of “cycles per second” for a wave, or the number of times a wave crest passes through a point in space per second. The higher the frequency, the higher the energy in the wave
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List the colors of visible light in order of increasing energy. red, orange, yellow, green, blue, violet
- a) Indicate the wavelength of each wave in the following wave diagrams.
b) Which of the waves has a higher frequency? Wave B
c) Which of the waves has a lower energy? Wave A
Wave A
Wave B
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As wavelength gets shorter, frequency increases.
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As wavelength gets shorter, energy increases.
- Describe the Bohr model of the atom, including the evidence collected that led to its development.
Nucleus at center with protons and neutrons; successive energy levels containing electrons surround nucleus. Bohr’s model was based upon evidence from line spectra, namely the emission spectrum for hydrogen
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What is the difference between a bright line spectrum and a continuous spectrum? How do energy levels account for the appearance of bright line spectra? bright line spectra show only distinct, finite colors (not an infinite amount. Continuous spectra show a fully blended rainbow of color with no gaps between. Bright line spectra are produced by electron jumping between energy levels. Since there are only a certain amount of jumps between levels possible, only a certain amount of colors can be produced. This shows up as the bright line spectrum
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What is the electromagnetic (EM) spectrum? The spectrum of all types of light in the universe (visible and non-visible) What is the highest energy wave? gamma Lowest? radio
- Consider this diagram of an atom with arrows representing electron movement.
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Which two arrows correspond to energy absorption by the atom? B and D
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Which two arrows correspond to energy emission by the atom? A nd C
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If violet and green light are produced by the movement illustrated here, which arrow represents emission of violet light? A green light? C
- Consider the spectroscopy lab. How did the flame tests you performed on different metals relate to firework production? Why did each metal produce a different color flame when excited?
Different elements give off different colors of light when excited. For example, copper glows green/blue, lithium glows red, etc. These metal salts can be added to fireworks to produce the desired color. They each produce unique colors because they each have a different arrangement of energy levels.
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Consider the spectroscopy lab. What caused the gas in the tubes to glow? How does this topic relate to “neon” sign production? Why is the term “neon sign” a bit misleading? The gas glowed when we added electrical energy to it from the outlet. The energy excited the electrons, making them jump to a higher energy level. When they jumped back down, light was released. Different gases can be added to glass tubes to give different colored glows, like in neon signs. Since not all of these signs are filled with neon, they aren’t truly all neon signs.
- Consider the spectroscopy lab. How did we know that pickles contain large amounts of sodium ion?
When the pickle was electrified, it glowed an orange/yellow color, just like the sodium salt we burned.
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How do scientists use bright line spectra to identify unknown elements in far off stars or other samples of matter? Known samples of elements are studied and the bright line spectrum is recorded. These known spectra can be compared to the unknown spectra seen when looking at the light from a far away star through a spectroscope. The knowns can be compared to the unknowns for identification purposes
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Consider only the first four primary energy levels of a hydrogen atom. The transition that would result in photon of the shortest wavelength would be
a) from n = 4 to n = 1 b) from n = 4 to n = 3
c) from n = 2 to n = 1 d) from n = 1 to n = 4
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Consider only the first four primary energy levels of a hydrogen atom. The transition that would result in photon of the longest wavelength would be
a) from n = 4 to n = 1 b) from n = 4 to n = 3
c) from n = 2 to n = 1 d) from n = 1 to n = 4
- The Lyman series of bright lines in the hydrogen atom are due to electrons dropping to the first energy level, the Balmer series are due to electrons dropping to the second energy level. Which one of these series is U.V. and which is visible? Explain.
The Lyman series refers to lines emitted in the UV region (electron transitions to level 1 are high energy transitions). The Balmer series refers to lines emitted in the visible region (electron transitions to level 2 are lower in energy than transitions to level 1)
- How do waves of red light and blue light differ with respect to frequency? wavelength? energy?
red: lower frequency and energy, longer wavelength
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How many electrons can a single atomic orbital hold? 2 How many orbitals can be found in an s sublevel? 1 p? 3 d? 5 f? 7
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“s” sublevels can hold a total of _2__ electrons. p sublevels can hold _6__ electrons, while d sublevels can hold _10__, and f sublevels can hold _14__ electrons.
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Which is bigger, the 3s sublevel or the 5s sublevel? How many electrons can each hold? 5s is bigger, but they both hold 2 electrons
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What are valence electrons and why are they important? outermost electrons, these are important because they determine an element’s chemical reactivity What is the octet rule? Each element wants to have 8 valence electrons
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Every element wants a full outer energy level (valence level). This is normally _8__ electrons, although in the case of helium it is _2___ electrons.
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An atom is in the ground state when the electrons in an atom are in the lowest possible energy levels.
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An atom is in the excited state when one or more electrons moves to a higher than normal energy level.
- Which of the following has the highest energy?
A) 4d B) 5s C) 5p D) 3p
- Which of the following has the lowest energy?
A) 6s B) 5p C) 4f D) 6p
- Give electron complete configurations for:
Na+ (1s22s22p6)
Fe (1s22s22p63s23p64s23d6)
Br (1s22s22p63s23p64s23d104p5)
Ar (1s22s22p63s23p6)
Al+3 (1s22s22p6)
O-2 (1s22s22p6)
He (1s2)
Ni+2 (1s22s22p63s23p63d8),
U (1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f 4)
Ag (1s22s22p63s23p64s23d104p65s24d9),
K (1s22s22p63s23p64s1)
Ne (1s22s22p6).
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Give shorthand electron configurations for: Ag [Kr] 5s24d9, I [Kr] 5s24d105p5, Rb [Kr] 5s1, Au [Xe] 6s24f145d9, Cu [Ar] 4s13d10, S-2 [Ar]
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What does isoelectronic mean same electron configuration (same # of electrons)? Give three elements that are isoelectronic with Kr. Se-2, Br-1, Rb+1, Sr+2
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1s22s22p63s23p4 is the electron configuration for which element? How many valence electrons does the element have? Sulfure; 6 valence electrons
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1s22s22p63s23p64s23d104p6 is the electron configuration for which noble gas? How can you use its electron configuration to confirm it is a noble gas?
Kr; Since 4 is the highest principle energy level reached, you need to count the number of electrons in level 4 (both from 4s and 4p) There are 2 electrons in 4s and 6 in 4p, 2 and 6 add up to 8 which, according to the octet rule, is stable.
