Periodic Structure and Trends

Alkali metals are characterized by which of the following? Select all that apply.

Reactivity with water

Ability to donate an electron

Ability to be pulled into a wire

A single valence electron in their ground state

All of the above

Which of the following elements are noble gases? Select all that apply.

Hydrogen

Helium

Xenon

Iodine

Helium, xenon

Which element has the highest effective nuclear charge?

Boron

Carbon

Nitrogen

Oxygen

Oxygen→ Z_eff increases across a period because of the increased number of protons in the nucleus, so oxygen has the highest effective nuclear charge of the options presented here.

Of the atoms listed below, which will have the largest atomic radius?

K

K+

Mg

Mg2+

K→ Atomic radius increases as you move down and left the periodic table. Therefore, potassium will generally have a larger radius than magnesium. However, be careful when dealing with charged species. Potassium that has been ionized has lost an electron, gaining the electron configuration of argon. This causes its effective nuclear charge to be distributed over fewer electrons, pulling them closer and reducing the radius of the ion. The uncharged species is thus larger than K⁺.

Which of the following elements has the highest first ionization energy?

Silicon

Fluorine

Phosphorus

Oxygen

Fluorine→ Ionization energy increases from left to right across a period and up a group. Therefore, fluorine will have the highest first ionization energy.

Which of the following elements are likely to have the most similar properties? Select two elements below.

Sodium

Beryllium

Fluorine

Phosphorus

Chlorine

Silicon

Fluorine, chlorine→ Chlorine, like fluorine, has seven valence electrons. These two are in the same column and have similar chemical characteristics.

Alkali metals, when placed in water, are highly reactive and sometimes capable of causing large explosions. Which property can explain this reactivity?

Alkali metals have 7 valence electrons

Alkali metals readily accept electrons

Alkali metals tend to form cations

Alkali metals are catalysts in combustion reactions

Alkali metals tend to form cations→ Members of the alkali metals have one valence electron. When this electron is lost, these elements become a cation with a noble gas configuration, making them very stable. For this reason, alkali metals can lose an electron extremely easily, making them highly reactive in water.

Why are noble gases unreactive in nature? Select all that apply.

They form stable diatomic molecules

They possess complete valence shells

They have highly stable, half-full valence shells

They tend to exist in an inert crystalline form

They possess complete valence shells→ Noble gases are inert because they already possess a full, eight electron valence shell. This configuration displays maximum stability.

Zeff increases across which directions on the periodic table?

Right and up

Right and down

Left and up

Left and down

Right and up→ When you move across a period, atomic number goes up, which means that the number of protons in the nucleus goes up, increasing Z_eff. When you move down a period, however, the shielding effect and the distance between the nucleus and the valence electrons goes up, causing the force on the valence electrons to go down. For this reason, Z_eff goes down as you move down the periodic table, despite the increasing charge of the nuclei.

Which of the following ions has the largest radius?

Cl-

K+

S2-

Ca2+

S2- → S2- has the largest radius. All of these ions have the same electron configuration, so they are isoelectronic. With the same electron configuration, the dication will have the smallest radius and the dianion the largest.

Electron repulsions increase when an electron is added to a valence shell, and the average nuclear attractive force per electron decreases, so anions are larger than the neutral element. In contrast, removing an electron decreases electron repulsions, and the average nuclear attractive force per electron increases, so cations have a smaller radius than the neutral element. The effects are enhanced by adding or removing additional electrons. The radius of K+ will be smaller than that of Cl-, so the correct order in terms of increasing ionic radius is Ca2+ < K+ < Cl- < S2-. The corresponding actual values in pm are: 100, 138, 181, 184.

Which of these elements has the greatest first ionization energy, IE1?

Sodium

Sulfur

Chlorine

Magnesium

Chlorine→ All of these elements are in the third row of the periodic table. More energy is required to remove an electron that is closer to the positive nucleus. Therefore, ionization energy generally increases as the atomic radius decreases from left to right across a period, and decreases as the radius increases moving down a group. Thus, chlorine should have the greatest IE1. For the elements listed the correct order for increasing ionic energy is sodium<magnesium<sulfur<chlorine. Corresponding actual values in kJ/mol are: 496, 738, 1000, 1251.

(Note: The additional stability associated with filled and half-filled shells, though, affects this general trend. For example, IE1 for phosphorus, with its half-filled valence shell, is greater than that of sulfur due to the greater stability of phosphorus’ half-filled p subshell.

Which of the following elements are found in the same period? Select all that apply.

Boron

Carbon

Nitrogen

Phosphorus

Arsenic

Boron, Carbon, Nitrogen

Which of the following terms is used to describe the group 2 elements?

Alkaline earth metals

Alkali metals

Transition metals

Nonmetals

Alkaline earth metals

Which of the following elements are transition metals? Select all that apply.

Germanium

Silver

Iron

Copper

Titanium

Silver, Iron, Copper, Titanium

Which of the following statements is true of the halogen group? Select all that apply.

The halogens have 7 valence electrons

None of the halogens are diatomic elements

The halogens are unreactive

The halogen group includes sulfur

The halogens have 7 valence electrons

Which element has the highest effective nuclear charge?

Fluorine

Chlorine

Bromine

Iodine

Fluorine→ When you move down a group, the shielding effect increases because there is another electron shell in the way, causing the force on the valence electrons to go down. For this reason, Z_eff decreases as you move down the periodic table, despite the increasing charge of the nuclei. Therefore, fluorine has the highest Z_eff of the options presented here.