Inorganic Chemistry - Problem Drill 13: Main Group Trends

Question No. 1 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed.

Knowing that -3 is the main oxidation state for phosphorus, that no other anions exist and the +1 state is unstable what two other possible stable oxidation states could exist?

A. +1 and +2 B. +2 and +3 C. +4 and +6 Question D. +3 and +5 E. +3 and +7

A. Incorrect! The question states that +1 is unstable.

B. Incorrect! These two states are only one electron apart.

C. Incorrect! Although the states are two electrons apart there are only five valence electrons +6 would be extremely unstable.

D. Correct! Feedback Phosphorus has the electron configuration of [Ne]3s23p3. The +3 state is to remove all 3 p electrons and become [Ne]3s23p3, which is a stable state. The +5 is to remove all 5 valence electrons, which is also a stable state according to the Octet Rule.

E. Incorrect! There are only five electrons in the valence so +7 would be very unstable.

Review the number of valence electronic states for the elements and the two electron rule. Phosphorus has the electron configuration of [Ne]3s23p3. The +3 state is to remove all 3 p electrons and become [Ne]3s23p3, which is a stable state. The +5 is to remove all 5 valence electrons, which is also a stable state according to the Octet Rule.

Solution

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Question No. 2 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed.

Which form of Phosphorus is the most unstable?

A. P8

B. P4 C. P2 Question D. Polymeric chain E. Rhombohedral

A. Incorrect! This would be a small piece of the red form, which is stable.

B. Correct! This is the white form that is tetrahedral with extreme ring strain, which makes it unstable.

C. Incorrect! White phosphorous dissociates to this more stable form at high temperature.

Feedback D. Incorrect! This is one of the most stable forms (red).

E. Incorrect This is one of the red forms and is stable.

Phosphorus exists in two main allotropes one white phosphorus is very reactive as tetrahedral P4 molecules. Since this cluster utilizes p-orbitals that are 90 degrees apart these bonds are extremely strained. White phosphorous ignites spontaneously in are and is very toxic.

Solution

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A fullerene is a molecule of carbon in the form of a hollow sphere, ellipsoid, tube, and many other shapes. Spherical fullerenes are also called buckyballs, What is the most symmetrical and stable monomeric fullerene below?

A. C20

B. C60 Question C. C180 D. C240 E. C540

A. Incorrect! This is the smallest known form. It is unstable and reactive.

B. Correct! This is the first isolated form. The most famous fullerene molecule is C60 with 12 pentagons and 20 hexagons, which is the most stable and symmetrical fullerene. C70 could be even more stable by some measure (heat of formation), but C60 has lower strain energy than C70.

C. Incorrect! This one has higher strain energy in its buckyball structure than C60.

Feedback D. Incorrect! This one has higher strain energy in its buckyball structure than C60.

E. Incorrect! This is one of the largest fullerenes, if not the largest.

Carbon is a very good example. The hardest most strongly bonded form of carbon is diamond with all carbon atoms in a tetrahedral arrangement. The most stable under standard conditions is graphite. Here we see how different it can be. Although it too is a network solid with covalent bonding the pi system which binds the layers together allow for electrons to move making graphite a non-metallic conductor. These were considered the only two primary allotropes until 1985 with the discovery of fullerenes. Since the discovery of the icosahedral C-60 spherical form all 23 isomers of this have been made as well as onions with many layers over the initial sphere. C-60 is highly symmetrical. It is also most stable. C70 could be even more stable by some measure (heat of formation), but C60 has lower strain energy than C70. Other spherical forms have also been discovered up to C-540. The higher carbon count and less stable it is. Solution

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Question No. 4 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed. Allotrope is each of two or more different physical forms in which an element can exist. Which element below could not form allotropes?

A. Nitrogen B. Sulfur C. Boron D. Phosphorus Question E. Polonium

A. Correct! As a diatomic molecule there are no possible allotropes.

B. Incorrect! Sulfur exists in a large number of allotropes.

C. Incorrect! Boron exists in a variety of allotropes.

Feedback D. Incorrect! Phosphorus exists in two major allotropes.

E. Incorrect! Although polonium is a metal there are two forms.

Remember that elements that exists as diatomic molecular species or are monatomic gases do not exist as allotropes. Nitrogen, as the diatomic covalent molecule N-2 and makes up the majority of our atmosphere. Azide and recently the cationic N-5 were discovered. The chemistry of nitrogen is dominated by oxides and to an extent the amine chemistry.

Solution

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 5 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed.

Knowing that lithium and magnesium have similar chemical behavior, this can be attributed to which property?

A. Density B. Melting Point C. Ionic Radii D. Ionization Energy Question E. Conductivity

A. Incorrect! Density is a physical property of an element related to its packing structure and may or may not be similar depending on which lattice form it adopts.

B. Incorrect! Melting point is a property of the metal bonding and is over 3 times larger for magnesium.

C. Correct! The similarities here are in the solubility of various ions of lithium and magnesium related to lattice energy and can be explained based on the similar size of the ions.

Feedback D. Incorrect! The ionization energy for magnesium is much higher than that of lithium.

E. Incorrect! Conductivity is another physical property based on the metallic nature of the element itself and not on its chemical properties in compounds.

Group 2 elements show similar trends to group 1. Radii increase with increasing mass. Ionization energy decreases. As mentioned earlier affinity values are positive because the process of adding an electron to this series is endothermic and requires energy rather than releasing energy.

Solution

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 6 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed.

If the oxidation state for nitrogen in NO is +2 What is the oxidation state for nitrogen in the molecule N2O3? Mentally rationalize your answer.

A. +2 B. +3 C. +4 D. +5 Question E. +6

A. Incorrect! The nitrogen to oxygen ratio is 1/1.5.

B. Correct! This would be the calculated value for each nitrogen atom. However, the molecule is not symmetrical

(O=N-N-O2) which give rise to one nitrogen with a +2 and one with a +4 oxidation state consistent with the 2 electron concept.

C. Incorrect! This would be the case for NO2

Feedback D. Incorrect! This would be the case for N2O5.

E. Incorrect! There are only 5 electrons in nitrogen’s valence.

Review oxidation number, the 2-electron concept and how to assign oxidations states from general chemistry. If oxygen is -2, nitrogen must be +3 to balance to neutral.

Solution

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 7 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed.

the electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion. Predict which element among below has the largest (exothermic) electron affinity?

A. K B. Ca C. N Question D. Se E. Cl

A. Incorrect! Potassium has one of the lowest electron affinities.

B. Incorrect! With one electron in its s orbital the pairing energy by additional of another electron makes this an endothermic process.

C. Incorrect! Nitrogen without close d orbitals to compensate has 3 unpaired electrons in its valence and so the addition of another electron requires additional energy to over come the pairing energy. This is endothermic.

Feedback D. Incorrect! Selenium has an electron affinity about 200 kJ/mol but is not the best answer.

E. Correct! Of your choices this is the best. The electron affinity values for the halogens are nearly 100kJ/mole greater than any of the other elements.

Electron affinity is the energy change when a neutral atom in the gas phase gains an extra electron. As you may have learned in general chemistry the trend is that electron affinity increases from left to right and decreases from top to bottom we will again see as mentioned before some diagonal similarities here as well. As you remember when a process give off energy the value is negative or exothermic.

Solution

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 8 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed.

In a periodic table, a group has three ways to name it. The group name is an identifier to describe the column in the table. Secondly, groups can also be identified by the first element in each group. Lastly, there are also common names for specific groups. What is the common name for group 15?

A. Alkali Metals B. Triels C. Halogens Question D. Pnicogens E. Tetrels

A. Incorrect! This is group 1.

B. Incorrect! This is group 13.

C. Incorrect! This is group 17.

Feedback D. Correct! Good job! These belong to group 15.

E. Incorrect! This is group 14.

Group 1 – Alkali metals Group 2 – Alkaline earth Group 13 – Triels (not an IUPAC approved name) Group 14 – Tetrels (not an IUPAC approved name) Group 15 – Pnicogens (not an IUPAC approved name) Group 16 – (not an IUPAC approved name) Group 17 – Halogens Group 18 – Nobel Gases Solution

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 9 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed.

Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first ionization energy of an atom or molecule is the energy required to remove one mole of electrons from one mole of isolated gaseous atoms or ions. If the first ionization energy of phosphorus is 1012 kJ/mol, what would you predict for the ionization energy of iodine?

A. 834 kJ/mol B. 1009 kJ/mol Question C. 1256 kJ/mol D. 577 kJ/mol E. 1402 kJ/mol

A. Incorrect! This is the value of antimony, down the same group.

B. Correct! Along the diagonal, the ionization energy should be very similar, hence 1009 kJ/mol.

C. Incorrect! This is the value of chlorine right in the period.

Feedback D. Incorrect! This is the value for aluminum left in the same period.

E. Incorrect! The value of nitrogen up the group.

Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first or initial ionization energy or Ei of an atom or molecule is the energy required to remove one mole of electrons from one mole of isolated gaseous atoms or ions. Along the diagonal, the ionization energy should be very similar, hence 1009 kJ/mol.

Solution

RapidLearningCenter.com  Rapid Learning Inc. All Rights Reserved Question No. 10 of 10 Instructions: (1) Read the problem statement and answer choices carefully, (2) Work the problems on paper as needed, (3) Pick the answer, and (4) Review the core concept tutorial as needed.

Most of the known compounds contain the strongly reducing fluorine or oxygen atoms. Which of the following is not a known compound of Xe?

A. XeF2 B. XeF8 C. XeClF4 D. XeO F Question 2 2 E. XeO4

A. Incorrect! Fluorine is the reason for the chemistry of the Nobel gases and the even numbered fluorides exist.

B. Incorrect! Fluorine is the reason for the chemistry of the Nobel gases and the even numbered fluorides exist.

C. Correct! No compounds with halides other than fluorine have been found and even if they are discovered this compound has an odd number of halides. It would be an anion.

Feedback D. Incorrect! Fluorine and of Xenon exist and the oxidation state is even.

E. Incorrect! The fully oxygenated molecule has been discovered and its oxidation number is even.

The Xe has a total of 8 outside shell electrons while the Fluorine 7 valence electrons. Xe's outside shell electrons are very far away from the center, therefore Xenon cannot possibly pay attention/attract all of the electrons. Fluorine is smaller, therefore is has a stronger positive attraction to the few electrons it has left. Fluorine is the only element that reacts with Xe because it is the most electronegative. Neil Bartlett was first to discover that the strong oxidizing agent could react with xenon. After the discovery many other compounds were discovered. Listed here are the reactive compounds.

Neutral compounds KrF2 XeF2, XeF4, XeF6, XeOF2, XeOF4, XeO2F2, XeO3F2, XeO3, XeO4

Solution

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