General Chemistry I Tutorial 2 PDF

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General Chemistry I Tutorial 2. Atoms 1. A charged particle is caused to move between two electrically charged plates, as shown here. 

(a) Why does the path of the charged particle bend? (b) What is the sign of the electrical charge on the particle? Negative

(c) As the charge on the plates is increased, would you expect the bending to increase, decrease, or stay the same? Increase

(d) As the mass of the particle is increased while the speed of the particles remains the same, would you expect the bending to increase, decrease, or stay the same?  Decrease

2. The following diagram is a representation of 20 atoms of a fictitious element, which we will call nevadium (Nv). The red spheres are 293Nv, and the blue spheres are 295 Nv. (a) Assuming that this sample is a statistically representative sample of the element, calculate the percent abundance of each element. 12 red and 8 blue so 60% red and 40% blue (b) If the mass of 293Nv is 293.15 amu and that of 295Nv is 295.15 amu, what is the atomic weight of Nv?  mNv= 293.15x60%+295.15x40%=

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3. Which of the following diagrams most likely represents an ionic compound, and which represents a molecular one? Explain your choice.

(i) is an ionic compound

4. A chemist finds that 30.82 g of nitrogen will react with 17.60, 35.20, 70.40, or 88.00 g of oxygen to form four different compounds. (a) Calculate the mass of oxygen per gram of nitrogen in each compound. (b) How do the numbers in part (a) support Dalton’s atomic theory?  5. The radius of an atom of gold (Au) is about 1.35 A° . (a) Express this distance in nanometers (nm) and in picometers (pm). (b) How many gold atoms would have to be lined up to span 1.0 mm? (c) If the atom is assumed to be a sphere, what is the volume in cm3 of a single Au atom? 6. Which of the following pairs of atoms are isotopes of one another? (a) 11B and 11C (b) 55Mn and 54Mn (c) 118Sn and 120Sn

no yes yes

7. How many protons, neutrons, and electrons are in the following atoms? (a) 40Ar (b) 65Zn (c) 70Ga (d) 80Br (e) 184W (f) 243Am.  8. Fill in the gaps in the following table, assuming each column represents a neutral

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atom. 

9. Only two isotopes of copper occur naturally, 63Cu (atomic mass = 62.9296 amu; abundance 69.17%) and 65Cu (atomic mass = 64.9278 amu; abundance 30.83%). Calculate the atomic weight (average atomic mass) of copper. 10. Naturally occurring magnesium has the following isotopic abundances:

(a) What is the average atomic mass of Mg? (b) Sketch the mass spectrum of Mg. 11. For each of the following elements, write its chemical symbol, determine the name of the group to which it belongs, and indicate whether it is a metal, metalloid, or nonmetal: (a) potassium (b) iodine (c) magnesium (d) argon (e) sulfur. 

12. Each of the following elements is capable of forming an ion in chemical reactions. By referring to the periodic table, predict the charge of the most stable ion of each: (a) Mg

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(b) Al (c) K (d) S (e) F. 13. Using the periodic table, predict the charges of the ions of the following elements: (a) Ga (b) Sr (c) As (d) Br (e) Se.  14. Using the periodic table to guide you, predict the chemical formula and name of the compound formed by the following elements: (a) Ga and F (b) Li and H (c) Al and I (d) K and S.  15. Predict whether each of the following compounds is molecular or ionic: (a) B2H6 (b) CH3OH (c) LiNO3 (d) Sc2O3 (e) CsBr (f) NOCl (g) NF3 (h) Ag2SO4 16. The diameter of a rubidium atom is 4.95 A ° . We will consider two different ways of placing the atoms on a surface. In arrangement A, all the atoms are lined up with one another to form a square grid. Arrangement B is called a close-packed arrangement because the atoms sit in the “depressions” formed by the previous row of

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atoms: 

(a) Using arrangement A, how many Rb atoms could be placed on a square surface that is 1.0 cm on a side? (b) How many Rb atoms could be placed on a square surface that is 1.0 cm on a side, using arrangement B? (c) By what factor has the number of atoms on the surface increased in going to arrangement B from arrangement A? If extended to three dimensions, which arrangement would lead to a greater density for Rb metal?  17. The element oxygen has three naturally occurring isotopes, with 8, 9, and 10 neutrons in the nucleus, respectively. (a) Write the full chemical symbols for these three isotopes. (b) Describe the similarities and differences between the three kinds of atoms of oxygen. 18. From the molecular structures shown here, identify the one that corresponds to each of the following species: (a) chlorine gas (b) propane (c) nitrate ion (d) sulfur trioxide (e) methyl chloride, CH3Cl. 

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19. A particular coal contains 2.5% sulfur by mass. When this coal is burned at a power plant, the sulfur is converted into sulfur dioxide gas, which is a pollutant. To reduce sulfur dioxide emissions, calcium oxide (lime) is used. The sulfur dioxide reacts with calcium oxide to form solid calcium sulfite. (a) Write the balanced chemical equation for the reaction. (b) If the coal is burned in a power plant that uses 2000 tons of coal per day, what mass of calcium oxide is required daily to eliminate the sulfur dioxide? (c) How many grams of calcium sulfite are produced daily by this power plant? 

Tutor section 3: Electronic Structure of Atoms 1. A certain quantum mechanical system has the energy levels shown in the accompanying diagram. The energy levels are indexed by a single quantum number n that is an integer.

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(a) As drawn, which quantum numbers are involved in the transition that requires the most energy? (b) Which quantum numbers are involved in the transition that requires the least energy? (c) Based on the drawing, put the following in order of increasing wavelength of the light absorbed or emitted during the transition: (i) n = 1 to n = 2 (ii) n = 3 to n = 2 (iii) n = 2 to n = 4 (iv) n = 3 to n = 1.

2. The contour representation of one of the orbitals for the n = 3 shell of a hydrogen atom is shown as follows. (a) What is the quantum number l for this orbital? (b) How do we label this orbital? (c) In which of the following ways would you modify this sketch to show the analogous orbital for the n = 4 shell: (i) It doesn’t change, (ii) it would be drawn larger, (iii) another lobe would be added along the +x axis, or (iv) the lobe on the +y axis would be larger than the lobe on the - y axis?

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3. The accompanying drawing shows part of the orbital diagram for an element. (a) As drawn, the drawing is incorrect. Why? (b) How would you correct the drawing without changing the number of electrons? (c) To which group in the periodic table does the element belong? 

4. State where in the periodic table these elements appear: (a) elements with the valence-shell electron configuration ns2np5 (b) elements that have three unpaired p electrons (c) an element whose valence electrons are 4s24p1(d) the d-block elements

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5. (a) Consider the following three statements: (i) A hydrogen atom in the n = 3 state can emit light at only two specific wavelengths, (ii) a hydrogen atom in the n = 2 state is at a lower energy than the n = 1 state, and (iii) the energy of an emitted photon equals the energy difference of the two states involved in the emission. Which of these statements is or are true? (b) Does a hydrogen atom “expand” or “contract” as it moves from its ground state to an excited state?  6. Is energy emitted or absorbed when the following electronic transitions occur in hydrogen? (a) from n = 4 to n = 2 (b) from an orbit of radius 2.12 Å to one of radius 8.46 Å (c) an electron adds to the H+ ion and ends up in the n = 3 shell?  7. Order the following transitions in the hydrogen atom from smallest to largest frequency of light absorbed: n = 3 to n=6 n=4 to n=9 n=2 to n=3 n=1 to n=2.  8. (a) For n = 4, what are the possible values of l? (b) For l = 2, what are the possible values of ml? (c) If ml is 2, what are the possible values for l? 9. Give the numerical values of n and l corresponding to each of the following orbital designations: (a) 3p, (b) 2s, (c) 4f, (d) 5d. 10. Which of the following represent impossible combinations of n and l? (a) 1p, (b) 4s, (c) 5f, (d) 2d  11. For the table that follows, write which orbital goes with the quantum numbers. Don’t worry about x, y, z subscripts. If the quantum numbers are not allowed, write “not allowed.” 

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12. What is the maximum number of electrons that can occupy each of the following subshells? (a) 3p, (b) 5d, (c) 2s, (d) 4f. 13. (a) What are “valence electrons”? (b) What are “core electrons”? (c) What does each box in an orbital diagram represent? (d) What quantity is represented by the half arrows in an orbital diagram? 14. Write the condensed electron configurations for the following atoms, using the appropriate noble-gas core abbreviations: (a) Cs, (b) Ni, (c) Se, (d) Cd, (e) U, (f) Pb. 15. Write the condensed electron configurations for the following atoms and indicate how many unpaired electrons each has: (a) Mg, (b) Ge, (c) Br, (d) V, (e) Y, (f) Lu. 16. The following electron configurations represent excited states. Identify the elements and write its ground state condensed electron configuration. (a) 1s22s22p43s1 (b) [Ar]4s13d104p25p1 c) [Kr]5s24d25p1 17. Determine whether each of the following sets of quantum numbers for the hydrogen atom are valid. If a set is not valid, indicate which of the quantum numbers have a value that is not valid. (a) n=4, l=1, ml = 2, ms = -1/2 (b) n= 4, l= 3, ml = -3, ms = + 1/2

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(c) n = 3, l = 2, ml = -1, ms = +1/2 (d) n = 5, l = 0, ml = 0, ms = 0 e) n = 2, l = 2, ml= 1, ms= +1/2 18. For orbitals that are symmetric but not spherical, the contour representations suggest where nodal planes exist (that is, where the electron density is zero). For example, the px orbital has a node wherever x = 0. This equation is satisfied by all points on the yz plane, so this plane is called a nodal plane of the px orbital. (a) Determine the nodal plane of the pz orbital (b) What are the two nodal planes of the dxy orbital? (c) What are the two nodal planes of the dx2 - y2 orbital?

19. Using the periodic table as a guide, write the condensed electron configuration and determine the number of unpaired electrons for the ground state of ( a) Br, (b) Ga, (c) Hf, (d) Sb, (e) Bi, (f) Sg. 20. Scientists have speculated that element 126 might have a moderate stability, allowing it to be synthesized and characterized. Predict what the condensed electron configuration of this element might be.

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21. In the experiment shown schematically below, a beam of neutral atoms is passed through a magnetic field. Atoms that have unpaired electrons are deflected in different directions in the magnetic field depending on the value of the electron spin quantum number. In the experiment illustrated, we envision that a beam of hydrogen atoms splits into two beams. (a) What is the significance of the observation that the single beam splits into two beams? (b) What do you think would happen if the strength of the magnet were increased? (c) What do you think would happen if the beam of hydrogen atoms were replaced with a beam of helium atoms? Why? (d) The relevant experiment was first performed by Otto Stern and Walter Gerlach in 1921. They used a beam of Ag atoms in the experiment. By considering the electron configuration of a silver atom, explain why the single beam splits into two beams.

22. Microwave ovens use microwave radiation to heat food. The energy of the microwaves is absorbed by water molecules in food and then transferred to other components of the food. (a) Suppose that the microwave radiation has a wavelength of 11.2 cm. How many photons are required to heat 200 mL of coffee from 23 to 60 °C? (b) Suppose the microwave’s poweris 900 W (1 watt = 1 joule/ second). How long would you have to heat the coffee in the part (a).

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