Periodicity

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Question 1Which element shows chemical behaviour similar

to calcium?

sodium boron

chlorinestrontium

Wrong Answer!Strontium and calcium both in group 2

II and III only

Question 2The following are three statements concerning the periodic

table.

I. The horizontal rows are periods and the vertical columns are called groups.

II. Electronegativity decreases down any group and across a period from left to right.

III.Reactivity increases down all groups.

I and II only

I, II and III

I only

Wrong Answer!Electronegativity increases across a period from left to right. Reactivity decreases down group 7.

Question 3

Which is the correct trend(left to right) across period 3 for the oxides?

neutral to acidic increasingly basic

basic to acidicacidic to basic

Wrong Answer!Reactive metals form basic oxides; reactive non-metals form acidic oxides.

Question 4

What happens when chlorine water is added to an aqueous solution of potassium iodide?

No reaction occurs because chlorine is less reactive than iodine.

Chlorine molecules are oxidized to chloride ions.

A purple precipitate of iodine is formed.

Iodide ions are oxidized to iodine molecules.

Wrong Answer!Chlorine oxidizes the iodide ions:

Cl2(aq) + 2I-(aq) 2Cl-(aq) + I2(aq)

Chlorine is a more powerful oxidising agent than iodine.

Question 5

In general, atomic radii decrease:

within a period from lower to higher atomic number.

within a group from lower to higher atomic number.

with an increase in the shielding of the nuclear charge.

with an increase in the number of isotopes of an element.

Wrong Answer!Atomic radii decrease across a period due to the increase in nuclear charge. Additional electrons enter the same shell and only a small increase in shielding effect.

Question 6In general, how do ionisation energies vary as the

periodic table is crossed from left to right?

They remain constant. They decrease.

They increase.They increase to a maximum and then decrease.

Wrong Answer!Shielding increases slightly cross the period but this is more outweighed by the increase in nuclear charge.

Question 7Which one of the following series represents the

correct size order for the various iodine species?

I < I- < I+ I+ < I < I-

I- < I < I+I < I+ < I-

Wrong Answer!The removal of an electron from an iodine atom results in an increase in the nuclear charge experienced by the remaining electrons and hence the radius decreases. The addition of an electron increases the electron-electron repulsion and decreases the nuclear charge experienced by the electrons.

Question 8Which of the following has the lowest melting

point?

Si Al

MgNa

Wrong Answer!Alkali metals are soft metals with low melting point.

Question 9For which isoelectronic ions do ionic radii

decrease with increasing nuclear charge?

Both positive and negative ions

Neither positive or negative ions

Negative ions Positive ions

Wrong Answer!Removal of successive electrons increases the nuclear charge experienced by the remaining electrons. Additional of successive electrons increases the electron-electron repulsion and decreases the nuclear charge experienced by the electrons.

Question 10

Which atom has the smallest atomic radius?

37Rb

20Ca31Ga

35Br

Wrong Answer!Atomic radius decreases across the period. Each subsequent electron enters the same shell, the same increase in shielding effect is more than outweighed by the increase in nuclear charge.

Question 11Which of the following properties of the halogens

increase from F to I?

I. Atomic radius

II.Melting point

III.Electronegativity

I only I and III only

I and II only I , II and III

Wrong Answer!Atomic radii increase down group 7 due to the presence of additional electron shells, melting point increase down the group due to an increase in va der Waals’ forces caused by additional electrons.

Question 12Which one of the following elements has the

lowest first ionization energy?

Mg Na

LiB

Wrong Answer!Ionization energy decreases down a group and increases across a period.

Question 13

0.01 mol samples of the following oxides were added separately to 1 dm3 portions of water. Which will produce the most acidic solution?

Al2O3(s) Na2O(s)

SO3(g)SiO2(s)

Wrong Answer!Aluminium oxide, Al2O3 and silicon dioxide, SiO2 are insoluble; sodium oxide, Na2O turns sodium hydroxide solution (basic); sulfur trioxide, SO3 forms sulfruic acid, H2SO4 solution.

Question 14On the periodic table, groups of elements show

similarities in their chemical properties. This can be best explained by the

differences in the number of protons in the nucleus of the atoms.

similarities in the results of emission spectrum analysis of gaseous samples of a group.

differences in the number of neutrons in the nucleus of the atoms.

similarities in the electronic structures of the atoms.

Wrong Answer!Each member has the same number of valence electrons and hence form ions with the same charge or the same number of covalent bonds.

II and III only

Question 15Which properties are typical of of most non-metals in period

3 (Na to Ar)?

I. They form ions by gaining one or more electrons.

II. They are poor conductor of heat and electricity.

III.They have high melting points.

I and III only

I, II and III

I and II only

Wrong Answer!Most non-metals have low melting points because they are simple molecular substances.

Congratulations!