Chapter 7 Periodic Properties of the Elements

Chapter 7 Periodic Properties of the Elements 1. Elements in the modern version of the periodic table are arranged in order of increasing. (a). oxidation number (b). atomic mass (c). average atomic mass (d). atomic number Explanation: The older version of the periodic table had the elements arranged in order of increasing atomic mass, but the modern version of the periodic table is based on the increasing order of atomic number. 2. The first ionization energies of the elements as you go from left to right across a period of the periodic table, and as you go from the bottom to the top of a group in the table. (a). increase, increase (b). increase, decrease (c). decrease, increase (d). decrease, decrease Explanation: The ionization energies (IE s) of elements increase to the right in a row since larger amounts of energy need to be supplied to remove an electron. The elements become more non-metallic making it harder to remove an electron. 3. The have the most negative electron affinities (a). alkaline earth metals (b). alkali metals (c). halogens (d). transition metals Explanation: The electron affinity of an element is defined as the energy change that occurs when an electron is added to a gaseous atom. The halogens have the most negative electron affinities indicating that they are most comfortable accepting an electron. The formation of an anion essentially gives the halogen atom the electron configuration of the nearest noble gas. The negative sign here indicates that the addition of an electron to the halogens results in energy being released by the halogen atom. Copyright 2006 Dr. Harshavardhan D. Bapat 1

4. Element M reacts with chlorine to form a compound with the formula MCl 2. Element M is more reactive than magnesium and has a smaller radius than barium. This element is. (a). Sr (b). K (c). Na (d). Ra Explanation: The formula of the compound MCl 2 indicates that M must have 2+ charges on it and it must be an alkaline-earth metal. Element reactivity and atomic radius typically increase down the group, which means that the element could be Ca or Sr. Since Sr is the only option that fits the answer is Sr. 5. The oxide of which element below can react with hydrochloric acid? (a). sulfur (b). selenium (c). sodium (d). nitrogen Explanation: For the oxide to react with hydrochloric acid, it must be a basic oxide. Only metals form basic oxides and out of the options provided, sodium is the only metal. 6. Metals can be at room temperature. (a). liquid only (b). solid only (c). solid or liquid (d). solid, liquid, or gas Explanation: Most metals are solids at room temperature with one prominent exception, which is mercury. 7. Na reacts with element X to form an ionic compound with the formula Na 3 X. Ca will react with X to form. (a). CaX 2 (b). CaX (c). Ca 2 X 3 (d). Ca 3 X 2 Explanation: The element X must have 3 negative charges for it to form the compound Na 3 X, since each Ca has 2 positive charges, the formula of the compound formed by the reaction of Ca and X would have to be Ca 3 X 2. Copyright 2006 Dr. Harshavardhan D. Bapat 2

8. What is the coefficient of M when the following equation is completed and balanced if M is an alkali metal? M (s) + H 2 O (1) (a). 1 (b). 2 (c). 3 (d). 0 Explanation: For this equation to be balanced the products would be MOH and H 2 gas and 2 moles of M would be needed. 9. Oxides of the active metals combine with water to form. (a). metal hydroxides (b). metal hydrides (c). water and a salt (d). oxygen gas 10. Oxides of the active metals combine with acids to form. (a). hydrogen gas (b). metal hydrides (c). water and a salt (d). oxygen gas 11. Oxides of most nonmetals combine with water to form. (a). an acid (b). a base (c). water and a salt (d). water Explanation: Most nonmetal oxides will combine with water to produce an acidic solution, while most metal oxides will combine with water to produce a basic solution. 12. The element phosphorus exists in two forms in nature called white phosphorus and red phosphorus. These two forms are examples of. (a). isotopes (b). allotropes (c). azeotropes (d). metrotropes Explanation: Allotropes are different forms of the same element in the same state. Copyright 2006 Dr. Harshavardhan D. Bapat 3

13. Of the hydrogen halides, only is a weak acid. (a). HC1 (aq) (b). HBr (aq) (c). HI (aq) (d). HF (aq) 14. Of the halogens, which are gases at room temperature and atmospheric pressure? (a). fluorine, bromine, and iodine (b). fluorine, chlorine, and bromine (c). fluorine, chlorine, bromine, and iodine (d). fluorine and chlorine Explanation: Of the 4 common halogens, bromine is a liquid at room temperature and pressure while iodine is a solid. 15. The only noble gas that does not have the ns 2 np 6 valence electron configuration is. (a). radon (b). neon (c). helium (d). krypton Explanation: Helium has only 2 electrons and thus does not have the ns 2 np 6 electron configuration like all other noble gases. 16. Atomic radius generally increases as we move. (a). down a group and from right to left across a period (b). up a group and from left to right across a period (c). down a group and from left to right across a period (d). there is no trend Explanation: The outermost electrons are added to new shells down a group while they are added to the same shell across a row. Thus atomic radius increase down a group but reduces from the left to the right across a row. Copyright 2006 Dr. Harshavardhan D. Bapat 4

17. Screening by the valence electrons in atoms is. (a). less efficient than that by core electrons (b). more efficient than that by core electrons (c). essentially identical to that by core electrons (d). both more efficient than that by core electrons and responsible for a general increase in atomic radius going across a period. Explanation: Screening by the core electrons (the electrons that are in the inner shells) would be more efficient than that by the valence electrons since the valence electrons are in the outermost shell and thus quite far away from the nucleus compared to the core electrons. 18. The atomic radius of main-group elements generally increases down a group because. (a). effective nuclear charge increases down a group (b). effective nuclear charge decreases down a group (c). both effective nuclear charge increases down a group and the principal quantum number of the valence orbitals increases (d). the principal quantum number of the valence orbitals increases 19. Which of the following correctly lists the five atoms in order of increasing size (smallest to largest)? (a). O < F < S < Mg < Ba (b). F < O < S < Mg < Ba (c). F < O < S < Ba < Mg (d). O < F < S < Ba < Mg Explanation: Fluorine and oxygen are in the same period (#2) and next to each other with F being the smallest of these 5 atoms. Ba is in group 2A and in row 6 (farthest down a group) and is the largest of the atoms. Mg is in group 2A and in the third period and hence will be bigger than F, O and S. Even though S is in the same period as Mg it is in group 6A making it smaller than Mg. 20. Which of the following correctly lists the five atoms in order of increasing size (smallest to largest)? (a). F < K < Ge < Br < Rb (b). F < Ge < Br < K < Rb (c). F < K < Br < Ge < Rb (d). F < Br < Ge < K < Rb Explanation: Fluorine is in group 7A and period 2 making it the smallest of the 5 atoms here. Br is also in group 7A but is in period 4 making it larger than F, Ge is in Copyright 2006 Dr. Harshavardhan D. Bapat 5

group 4A and also in period 4 but is to the left of Br making it larger than Br. K and Rb are both in group 1A but K is in period 4 and Rb is in period 5, making the Rb atom the largest of all the 5 atoms. 21. Of the following atoms, which has the largest first ionization energy? (a). Br (b). O (c). C (d). P Explanation: The ionization energy (IE) typically increases from left to right in a period and decreases from top to bottom in a group. Thus for C and O which are in the same period, O will have the larger IE. Br is in period #4 and will have the lowest IE out of these 4 elements. 22. Of the following elements, which has the largest first ionization energy? (a). Na (b). A1 (c). Se (d). C1 Explanation: The ionization energy (IE) typically increases from left to right in a period and decreases from top to bottom in a group. Na, Al and Cl are all in period 3 with the chlorine atom to the farthest right and will have the highest IE. 23. have the lowest first ionization energies of the groups listed. (a). Alkali metals (b). Transition elements (c). Halogens (d). Alkaline earth metals Explanation: The ionization energy (IE) is the minimum energy needed to remove an electron from the ground state of the isolated gaseous atom or ion. Of the groups listed in this question the elements in the alkali metals group will be the ones that are most willing to lose an electron (lowest first IE) since this will essentially lead to an ion with the electron configuration of the previous noble gas. 24. Which of the following has the largest second ionization energy? (a). Si (b). Mg (c). A1 (d). Na Copyright 2006 Dr. Harshavardhan D. Bapat 6

Explanation: The second ionization energy (IE) is the minimum energy needed to remove two electrons from the ground state of the isolated gaseous atom or ion. If an atom reaches a stable noble gas configuration after the removal of the first electron then naturally the second IE will be higher as it will resist losing its noble gas electron configuration. Of the 4 elements listed in this question, Na will have reached the noble gas configuration after losing one electron and will have the highest second IE. 25. Which of the following has the largest second ionization energy? (a). Ca (b). K (c). Ga (d). Ge Explanation: The second ionization energy (IE) is the minimum energy needed to remove two electrons from the ground state of the isolated gaseous atom or ion. If an atom reaches a stable noble gas configuration after the removal of the first electron then naturally the second IE will be higher as it will resist losing its noble gas electron configuration. Of the 4 elements listed in this question, K will have reached the noble gas configuration after losing one electron and will have the highest second IE. 26. Which equation correctly represents the first ionization of aluminum? (a). Al - (g) Al (g) + e - (b). Al (g) Al - (g) + e - (c). Al (g) + e - Al - (g) (d). Al (g) Al + (g) + e - 27. Which ion below has the largest radius? (a). C1 - (b). K + (c). Br - (d). F - Explanation: Typically cations are smaller than their parent atoms while anions are larger than the parent atoms. Of the atoms here, the Br atom would be the largest as it is farthest down the group and hence its anion also will be the largest ion. 28. The ion with the smallest radius is. (a). Br - (b). C1 - (c). O 2- (d). F - Copyright 2006 Dr. Harshavardhan D. Bapat 7

Explanation: Typically anions are larger than the parent atoms. Of the atoms here, the F atom would be the smallest as it is farthest down the group and hence its anion also will be the smallest ion. 29. Which of the following is an isoelectronic series? (a). B 5-, Si 4-, As 3-, Te 2- (b). O 2-, F -, Ne, Na + (c). S, C1, Ar, K (d). None of the above Explanation: Isoelectronic series contain a combination of atoms and ions or only ions with the same number of electrons. Here the series containing the O 2-, F -, Ne and Na + is the only one where all atoms/ions contain 10 electrons. 30. is isoelectronic with argon and is isoelectronic with neon. (a). C1 -, F - (b). C1 -, C1 + (c). F +, F - (d). Ne -, Kr + Explanation: The Cl - ion has 18 electrons and is isoelectronic with argon while the F - ion has 10 electrons making it isoelectronic with neon. 31. Chlorine is much more apt to exist as an anion than is sodium. This is because. (a). chlorine is bigger than sodium (b). chlorine has a greater ionization energy than sodium does (c). chlorine has a greater electron affinity than sodium does (d). chlorine is a gas and sodium is a solid 32. Which of the following is not a characteristic of metals? (a). acidic oxides (b). low ionization energies (c). malleability (d). ductility Explanation: Metals form basic oxides. Copyright 2006 Dr. Harshavardhan D. Bapat 8

33. When two elements combine to form a compound, the greater the difference in metallic character between the two elements, the great the likelihood that the compound will be. (a). a gas at room temperature (b). a solid at room temperature (c). metallic (d). nonmetallic Explanation: A large difference in the metallic character of elements would mean that the compound formed by the combination of these two elements will be ionic and a solid at room temperature. Copyright 2006 Dr. Harshavardhan D. Bapat 9