IB DP Chemistry Topic 3.2 Periodic trends SL Paper 1

Question

Which properties of the alkali metals decrease going down group 1?

A.     First ionization energy and reactivity

B.     Melting point and atomic radius

C.     Reactivity and electronegativity

D.     First ionization energy and melting point

▶️Answer/Explanation

D

The only factor affecting the size of the atom is the number of layers of inner electrons which surround the atom. More layers of electrons take up more space, due to electron-electron repulsion. Therefore, the atoms increase in size down the group. Hence, atomic radius increases down the group. 

The first ionization energy of an atom is defined as the energy required to remove the most loosely held electron from each of one mole of gaseous atoms, producing one mole of singly charged gaseous ions. the distance between the nucleus and the outer electrons increases down the group; electrons become easier to remove, and the ionization energy falls.

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. As the metal atoms increase in size, any bonding electron pair becomes farther from the metal nucleus, and so is less strongly attracted towards it. This corresponds with a decrease in electronegativity down Group 1.

Reactivity increases down the group as electrons becomes farther from the nucleus.

Both the melting and boiling points decrease down the group. When any of the Group 1 metals is melted, the metallic bond is weakened enough for the atoms to move more freely, and is broken completely when the boiling point is reached. The decrease in melting and boiling points reflects the decrease in the strength of each metallic bond.

Question

Which statements about the periodic table are correct?

I.     The elements Mg, Ca and Sr have similar chemical properties.

II.     Elements in the same period have the same number of main energy levels.

III.     The oxides of Na, Mg and P are basic.

A.     I and II only

B.     I and III only

C.     II and III only

D.     I, II and III

▶️Answer/Explanation

A

Statement 1 is correct because Mg, Ca and Sr all belong to the same group 2 in the periodic table.

Elements in the same period have same value on n hence, have same number of main energy levels.

Metals react with oxygen to give basic compounds of oxygen. Hence, oxides of Na and Mg are basic. S is a non metal, hence its oxide is acidic.

Question

The electronegativities of four different elements are given below (the letters are not their chemical symbols).

Elements: W,X,Y,Z

Electronegativities: 0.9, 1.2, 3.4, 4.0 respectively.

Based on this information which statement is correct?

A.     W is a non-metal.

B.     W and X form an ionic compound.

C.     Y is a metal.

D.     Y and Z form a covalent compound.

▶️Answer/Explanation

D

Electronegativity difference between W and X = 1.2-0.9 = 0.3, hence it will form non polar covalent compound.

Electronegativity difference between  Y and Z = 4-3.4 = 0.6, hence it will form polar covalent compound.

Metals have electronegativity less than 2, W is a metal. Y is a non metal. 

Question

Which property generally decreases across period 3?

A.     Atomic number

B.     Electronegativity

C.     Atomic radius

D.     First ionization energy

▶️Answer/Explanation

C

Going across period 3, as the atomic number increases, atomic radius decreases. 

Atomic number, electronegativity and first ionization energy all increases going across left to right in period 3.

Question

Which property increases down group 1?

A.     First ionization energy

B.     Melting point

C.     Reactivity

D.     Electronegativity

▶️Answer/Explanation

C

The reactions of the elements with water become more vigorous down the group.

When they do react they produce hydroxides and hydrogen. 

Hence, reactivity increases down group 1.

Question

Which combination of the characteristics of element X, a metal, and element Y, a non metal, is most likely to lead to ionic bonding?

M11/4/CHEMI/SPM/ENG/TZ1/12

▶️Answer/Explanation

A

For ionic bonding, metal should be able to form cation easily, so its ionization energy should be low. 

For ionic bonding, electronegativity difference between Y and X should be high(1.7 or above). Y should have high electronegativity value. 

Question

Which combination of properties best describes sodium oxide, \({\text{N}}{{\text{a}}_{\text{2}}}{\text{O}}\)?

M15/4/CHEMI/SPM/ENG/TZ2/08

▶️Answer/Explanation

B

As oxides of metals are basic. Sodium oxide is basic.

Electronegativity of Na is 0.93 and that of O is 3.44. Difference in electronegativity = 3.44-0.93 = 2.51 (>1.7) so, it will be an ionic compound. 

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