Chem chapter 3
How many core electrons does an atom of beryllium (Be) contain?
2 Beryllium (Be) has four electrons and an electron configuration of 1s2 2s2. The electrons in the 1st shell are in the core and the electrons in the outer shell are valence electrons
Now that you have the contribution from the X-19 isotope (1.982) and from the X-21 isotope (18.81), what is the average atomic mass (in amu) of this element using four significant figures?
20.79 amu 1.982+18.81 (0.1201)(19.00amu)+(0.8799)(21.00amu)=20.76amu
A student draws the orbital diagram below for the 3d electrons in a V atom. What, if anything, is incorrect about the drawing?
It violates Hund's rule. Hund's rule states that electrons are added to the atomic orbitals with the same energy levels (degenerate orbitals) in such a way that each orbital is occupied by a single electron with the same spin (either +½ or -½) before any orbital can be occupied by two electrons. In this student's diagram, one of the orbitals has two electrons while three orbitals at equal energies contain zero electrons, which is in violation of Hund's rule.
A student draws the orbital diagram below for the 3p electrons in an S atom. What, if anything, is incorrect about the drawing?
It violates Hunds rule Hund's rule states that electrons are added to the atomic orbitals with the same energy levels (degenerate orbitals) in such a way that each orbital is occupied by a single electron with the same spin (either +½ or -½) before any orbital can be occupied by two electrons. In this student's diagram, the two orbitals that contain a single electron have electrons with opposite spins (one is up and one is down), which is in violation of Hund's rule
An electron has the following set of quantum numbers: 3, 2, -1, -½. Which of the following atoms could have an electron in the ground state with these quantum numbers? Ne Ar Ca Kr
Kr An electron with n=3 and l=2 would be in the 3rd orbital. The only atom from the list which meets this criteria is Kr
Which of the following atom(s) below has/have five valence electrons? C N O F All of the above
N Elements in group 15 have 5 valence electrons. These include: N, P, As, Sb, Bi, and Mc
Valence electrons in which of the following atoms experience the greatest effective nuclear charge (Zeff)?
Ne The Zeff increases from left to right in the periodic table
Red light has a _____ frequency and a _____ wavelength than ultraviolet rays.
lower, longer As can be seen on the electromagnetic spectrum, red light (and all visible light) has a lower frequency, and therefore a longer wavelength, than ultraviolet rays.
Which of the following sets of quantum numbers is not allowed? A) n=3, l=2, ml=-2 B) n=4, l=3, ml=-3 C)n=2, l=1, ml=-1 D)n=2.5, l=0, ml=0 E)n=3, l=2, ml=-1
n = 2.5, ℓ = 0, mℓ = 0 According to the rules governing acceptable quantum numbers, the value for n must be an integer. Therefore, the set {n = 2.5, ℓ = 0, mℓ = 0} is not allowed.
A ground state atom of As could not have any electrons with which of the following configurations?
n = 4, ℓ = 2, mℓ = 0, ms = +½ A ground state As atom has the electronic structure 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3. The highest-energy orbital in this atom is 4p, which represents the quantum numbers n = 4, ℓ = 1. Of the options given, the set of quantum numbers with n = 4, ℓ = 2 is higher in energy than the highest occupied atomic orbital, so a ground state atom of As could not have any electrons with the set of quantum numbers n = 4, ℓ = 2, mℓ = 0, ms = +½
Consider the atom with the chemical symbol Ru. What is the name of this element?
ruthenium
Which of the following is true concerning ψ²?
ψ² describes the probability of finding an electron in space. While the wave function ψ describes the overall state of a quantum system, the square of the wavefunction (ψ2) gives the probability of finding an electron in a given region of space.
What is the energy of a mole of photons that have a wavelength of 693 nm? (h = 6.626 × 10⁻³⁴ J • s and c = 3.00 × 10⁸ m/s)
1.72 × 10⁵ J Energy of one mole photon (E) = (6.023x1023 x6.626x10−34J.s x 3x108ms−1)/(693x10−9m)
What is the energy of light that must be absorbed by a hydrogen atom to transition an electron from n = 3 to n = 7?
1.98 × 10⁻¹⁹ J The Bohr model of the atom states that the energy required to transition between two energy levels is equal to the difference between the inverse squares of the energy levels multiplied by the Rydberg constant:
There are two isotopes of an unknown element, X-19 and X-21. The abundance of X-19 is 10.43%. A weighted average uses the percentages of each isotope to scale their contribution to the total mass. Each isotope's contribution is the percentage (in decimal form) multiplied by the mass of the isotope. What is the contribution (in amu) to the weighted average from the X-19 isotope, which has a mass of 19.00 amu?
1.982 amu Example: The contribution from the X-19 isotope is found by multiplying the percentage by the mass of the isotope: (0.1201)(19.00amu) = 2.282amu
How many electrons in an atom can have the following quantum numbers? n = 6, ℓ = 2
10 The Pauli exclusion principle states that each electron in a given atom must be represented by a unique set of four quantum numbers (n, ℓ, mℓ, ms). Here, only two of the quantum numbers are specified. The maximum number of possible electrons in an atom is dictated by the quantum number ℓ, which in this case equals 2. The value for the quantum number mℓ must be between −ℓ and +ℓ, which means mℓ can equal -2, -1, 0, 1, 2. Because each of these values of mℓ has corresponding values n = 3 and ℓ = 2, this represents 5 unique orbitals. The fourth quantum number, ms, can equal +1/2 or -1/2, meaning each orbital can contain two electrons with unique sets of four quantum numbers. Since there are 5 orbitals with the capacity for 2 electrons each, there can be 10 electrons in the atom with n = 3 and ℓ = 2
There are two isotopes of an unknown element, X-19 and X-21. The abundance of X-19 is 10.43%. The percentage of the X-21 isotope is 89.57 % What is the contribution (in amu) to the weighted average from the X-21 isotope, which has a mass of 21.00 amu?
18.81 amu 21 x 89.57% Example: The contribution from the X-21 isotope be found by multiplying the percentage by the mass of the isotope.(0.8799)(21.00amu)=18.48amu
Write the complete ground-state electron configuration of Cu⁺. For multi-digit superscripts or coefficients, use each number in succession.
1s2 2s2 2p6 3s2 3p6 3d10 Half-filled and fully filled subshell have got extra stability. Therefore, one of the 4s2 electrons jumps to the 3d9. This give us the (correct) configuration of: 1s2 2s2 2p6 3s2 3p6 3d10 4s1 For the Cu+ ion we remove one electron from 4s1 leaving us with: 1s22s22p63s23p63d10
Write the complete ground-state electron configuration of magnesium. For multi-digit superscripts or coefficients, use each number in succession.
1s²2s²2p⁶3s² Magnesium the first two electrons will go in the 1s orbital. Since 1s can only hold two electrons the next 2 electrons for magnesium go in the 2s orbital. The next six electrons will go in the 2p orbital. The p orbital can hold up to six electrons. We'll put six in the 2p orbital and then put the remaining two electrons in the 3s. Therefore the Magnesium electron configuration will be 1s22s22p63s2.
Write the complete ground-state electron configuration of titanium.
1s²2s²2p⁶3s²3p⁶4s²3d² Titanium: 22
Write the complete ground-state electron configuration of arsenic. For multi-digit superscripts or coefficients, use each number in succession.
1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p³ Arsenic(As): Arsenic is a p-block element having atomic number 33. Arsenic belongs to group 15. Electronic configuration of Group 15: The valence shell electronic configuration of these elements is . These elements have completely filled s orbitals and half-filled p orbitals, making their electronic configuration extra stable. Electronic configuration of Arsenic: The electronic configuration of arsenic is 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p³
Which of the following electron configurations represent a transition metal atom?
1s²2s²2p⁶3s²3p⁶4s²3d⁷ The transition metals are in the d block of the periodic table, meaning their electron configurations will end with a partially or completely filled d orbital. Of these options, only 1s2 2s2 2p6 3s2 3p6 4s2 3d7 (Co) meets this criteria. (27 electrons)
Write the complete ground-state electron configuration of chromium.
1s²2s²2p⁶3s²3p⁶4s¹3d⁵ Half-filled and fully filled subshell have got extra stability. Therefore, one of the 4s2 electrons jumps to the 3d5 so that it is half-filled (see video below). This give us the (correct) configuration of: 1s2 2s2 2p6 3s2 3p6 3d5 4s1
What would be the charge on an atom of Ru which only has 41 electrons?
3 The charge of an atom is found by subtracting the number of electrons from the number of protons. If Ru has only 41 electrons, the charge equals +3: 44 protons - 41 electrons = +3.
An electron has the following set of quantum numbers: 3, 2, -1, -½. What is the energy level for this electron?
3 The first number listed is the energy level: n=3
If n = 4, what is the maximum allowed value for ℓ?
3 The maximum value of l for n = 4 is 3 ( l = n - 1)
In a multi-electron atom, which orbital will have the highest energy?
4f The energy of an electron is primarily dictated by its principal quantum number, n. For atoms with multiple electrons, electrons that have the same value of n (as is the case here, with n = 4) will have higher energies with higher values of ℓ. Of these options, the 4f orbital has the highest value of ℓ (ℓ = 3), so it will have the highest energy.
How many orbitals are allowed in the subshell when ℓ = 2?
5 A d subshell must have l = 2, and it therefore has five allowed values of ml: -2, -1, 0, +1, and +2. Since each of the five orbitals can hold two electrons, the 5d subshell can hold a maximum of 10 electrons. The Pauli exclusion principle states that each electron in a given atom must be represented by a unique set of four quantum numbers (n, ℓ, mℓ, ms). The value for the quantum number mℓ must be between −ℓ and +ℓ, which means mℓ can equal -2, -1, 0, 1, 2. Because each of these values of mℓ has corresponding value of ℓ = 2, this represents 5 unique orbitals.
Determine the energy of a photon with a wavelength of 363 nm. (h = 6.626 × 10⁻³⁴ J • s and c = 3.00 × 10⁸ m/s)
5.48 × 10⁻¹⁹ J E=hc/λ After converting the wavelength into meters, solve for the energy. 361 nm ×1m/109 nm=3.61×10−7 mE=hcλ=(6.626×10−34J⋅s)(3.00×108ms)/ 3.61×10−7 m=5.51×10−19 J
There are two isotopes of an unknown element, X-19 and X-21. The abundance of X-19 is 10.43%. What is the percentage of the X-21 isotope?
89.57% Example: The percentages of the two isotopes must add up to be 100%. So, if the percentage of the X-19 isotope is 12.01%, then the percentage of the X-21 isotope is 100% - 12.01% = 87.99%
What would be the mass number for an atom of Ru which has 55 neutrons?
99 (Atomic #44, 44+55) The mass number of an atom is the sum of the protons and neutrons. The number of protons equals the atomic number.
What type of element is Ru?
A transition metal
An electron has the following set of quantum numbers: 3, 2, -1, -½. What type of orbital is represented by these quantum numbers?
D - orbital A d-orbital has l=2
What happens to the energy of a photon if the wavelength is doubled?
Energy is reduced by one-half The energy (E) of a photo of light is proportional to its frequency (v) or the inverse of its wavelength (λ) multiplied by Planck's constant (h): E = hν = hc/λ As demonstrated by this equation, doubling the wavelength reduces the energy by half
Which of the following forms of radiation has the highest frequency?
Gamma rays electromagnetic spectrum ranges from radiation with the highest frequency (shortest wavelength) to lowest frequency (longest wavelength). Of the various types of radiation, gamma rays have the highest frequency
In the Bohr model of the hydrogen atom, the energy required to excite an electron from n = 2 to n = 3 is _______________ the energy required to excite an electron from n = 3 to n = 4?
Greater than The Bohr model of the atom states that the energy required to transition between two energy levels is equal to the difference between the inverse squares of the energy levels multiplied by a constant: ΔEi→f=R(1n2f−1n2i) This equation can be used to compare the energy required for different transitions. ΔE2→3=R(132−122)=−0.14R ΔE3→4=R(142−132)=−0.05R |ΔE2→3| > |ΔE3→4|
Which of the following series of isoelectronic ions (Mg²⁺, N³⁻, F⁻, Si⁴⁺) has the ionic radii in order of largest to smallest?
N³⁻ > F⁻ > Mg²⁺ > Si⁴⁺ isoelectronic species, anions will be larger than cations. Ions can be further ranked by considering their charges. The greater the negative charge, the larger the size. The greater the positive charge, the smaller the size
Which of the following would you expect to have the most negative (most exothermic) electron affinity? Li O K Se Rb
O Electron affinity generally becomes more exothermic as you move across a row and up a column. Oxygen atoms have the most exothermic electron affinity of this group.
Which of the following states that no two electrons can have the same set of four quantum numbers?
Pauli exclusion principle The Pauli exclusion principle states that no two electrons in a given atom can share the same set of four quantum numbers (n, ℓ, mℓ, ms).
What type of light on the electromagnetic spectrum has the lowest energy per photon?
Radio Energy is directly related to frequency and inversely related to wavelength. Since radio waves have the lowest frequency and longest wavelength, they have the lowest energy.
Which type of electromagnetic radiation has the largest wavelength?
Radio The electromagnetic spectrum ranges from radiation with the shortest wavelength (highest) to longest wavelength (lowest). Of the various types of radiation, radio waves have the longest wavelength.
Rank the following atoms in order of increasing first ionization energies (i.e., lowest to highest): Rb, F, Mg, B, N.
Rb < Mg < B < N < F In general, first ionization energy decreases down a group and increases across a period. Example: Since out of Rb, Li, N and F, Rb is at leftmost and lowermost of the periodic table, therefore it will be having lowest first ionization energy. Similarly F is at rightmost and uppermost of the periodic table, therefore it will be having highest first ionization energy. Now we have to rank N and Li :- Since N is in the right side of N, therefore N>>Li So, based on above explanation, correct order is :- Rb<<Li<<N<<F
Which of the following transition metals would be expected to have the smallest atomic radius? Y Zr Nb Tc Ru
Ruthenium (Ru) The atomic radius increases as you move down the periodic table and to the left. Ruthenium is the furthest to the right and the top of this list and it would be expected to have the smallest atomic radius
Which element has the ground state electron configuration [Kr]5s²4d¹⁰5p³?
Sb This electron configuration ends with 5p, meaning it is an element in the p block (a main group element on the right-hand side of the periodic table) in the fifth row. The 3 in 5p3 indicates that it is the third element in this row, so the element must be Sb
If a hydrogen (H) atom and a helium (He) atom travel at the same speed, which of the following is true about the de Broglie wavelengths of the atoms?
The H atom is about 4 times longer than the He atom. The de Broglie equation treats moving particles like waves, and states that the wavelength (λ) of these particles is inversely proportional to their momentum, or the product of their mass (m) and velocity (ν). λ=h/mv For two particles moving at the same speed, the particle with the greater mass will have a shorter wavelength, so He will have a shorter wavelength than H. Because H is about 4 times less massive than H, its wavelength will be 4 times longer than that of He.
In the photoelectric effect, if the intensity of light shone on a metal increases, what will happen?
There will be more electrons ejected In the photoelectric effect, photons with an energy of E are shone upon a piece of metal, and if the energy of the photons overcome the work function ϕ of the metal, then electrons with will be ejected from the metal with a kinetic energy KE. Ephoton=Φ + KE Each photon is capable of ejecting one electron from the metal. Therefore, increasing the intensity of the light (the number of photons shone on the metal) will increase the number of electrons ejected from the metal
Which of the following has the electron configuration 1s²2s²2p⁶3s²3p⁶3d³?
V²⁺ The ion with the electron configuration of 1s2 2s2 2p6 3s2 3p6 3d3 has a total of 21 electrons. Of the options given, the only ion with the same number of electrons is V2+, resulting from the electron configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d3 (23 total electrons) losing two electrons from the 4s orbital
Write the condensed (noble-gas) electron configuration of Fe²⁺.
[Ar]3d⁶ Iron electron configuration will be 1s22s22p63s23p64s23d6. Fe2+ ion we remove two electrons from 4s2 leaving us with: 1s22s22p63s23p63d6 18 electrons are present in noble gas Ar [Ar] 3d6
Which electron configuration violates Hund's rule?
[He]2s²2px²2py² Hund's rule states that electrons are added to the atomic orbitals with the same energy levels (degenerate orbitals) in such a way that each orbital is occupied by a single electron with the same spin before any orbital can be occupied by two electrons. Because there are three 2p orbitals, each of the individual 2p orbitals (2px,2py,2pz ) needs to have a single electron before any of them can have two electrons. Therefore, the electron configuration [He] 2s2 2px2 2py2 , which has two electrons in the 2px and 2py orbitals, but zero electrons in the 2pz orbital, is in violation of Hund's rule
