Chapter 7: Trends in the Periodic Table

Question 1

Atomic Radius/ Covalent Radius

Answer 1

The atomic radius of an atom is defined as half the distance between the nuclei of two atoms of the same element that are joined together by a single covalent bond.

Question 2

Why do the values of the atomic radius increase down the groups of the periodic table?

Answer 2

1. The additional electrons are going into a new energy level which is further from the nucleus. Since the outer electrons are becoming further away from the nucleus, the atomic radius increases.
2. Screening effect of the inner electrons.

Question 3

Why do the values of the atomic radius decrease across a period in the periodic table?

Answer 3

1. Increase in effective nuclear charge. As the number of protons increases from left to right across a period, the attractive force of the nucleus increases. This pulls electrons closer to it which makes the atomic radius decrease.
2. No increase in the screening effect. As there is no additional energy level of electrons being added to counteract the increasing attractive force of the nucleus, the atomic radius shrinks.

Question 4

First Ionisation Energy

Answer 4

The first ionisation energy of an atom is the minimum energy required to completely remove the most loosely bound electron from a neutral gaseous atom in its ground state.

Question 5

Second Ionisation Energy

Answer 5

is the energy required to remove an electron from an ion with one positive charge in the gaseous state.

Question 6

Why do the values of the first ionisation energy decrease down a group?

Answer 6

1. Increasing atomic radius. The atomic radius increases down the the groups of the periodic table .The outermost electrons are becoming further away from the attractive force of the nucleus. It becomes easier to remove an electron from the outer energy level.
2. Screening effect of the inner electrons. The outermost electrons are somewhat shielded from the attractive force of the positively charged nucleus and so are easier to remove.

Question 8

Why do the values of the first ionisation energy increase across a period?

Answer 8

1. Increasing effective nuclear charge. No. of protons increases from left to right across a period. The attraction between the nucleus and outer electrons increases. Electrons are being held more firmly so it requires more energy to remove an electron from the outermost energy level.
2. Decreasing atomic radius. Electrons in the outermost energy level are becoming closer to the nucleus. Therefore it it more difficult to remove an electron due to attraction between it and the nucleus.

Question 9

Electronegativity

Answer 9

is the relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond

Question 10

Why do the values of electronegativity increase across a period?

Answer 10

1. Increasing effective nuclear charge. No. of protons increases from left to right across a period. The attraction between the outer electrons and the nucleus steadily increases. Therefore electrons involved in bonding are more attracted to the nucleus. Electronegativity increases.
   2.Decreasing atomic radius. Electrons in the outermost energy level are becoming closer to the nucleus. Greater attraction between the nucleus and electrons so electronegativity increases.

Question 11

Why do the values of electronegativity decrease down a group?

Answer 11

1. Increasing atomic radius. Outermost electrons are becoming further away from the nucleus. Therefore there is a smaller attraction between the nucleus and the shared pair of electrons. Electronegativity decreases.
2. Screening effect of inner electrons. Outermost electrons are somewhat shielded by the attractive force of the positively charged nucleus so the electronegativity decreases.