Discuss and compare the trend in ionization enthalpy of the elements of group 1 with those of group 17 elements.

The trend in ionization enthalpy, or the energy required to remove an electron from an atom to form a positively charged ion, varies across different groups of the periodic table. Group 1 elements, also known as alkali metals, and Group 17 elements, also known as halogens, exhibit distinct trends in ionization enthalpy due to variations in atomic structure and electron configuration.

Group 1 (Alkali Metals):

1. Decreasing Ionization Enthalpy Down the Group: As we move down Group 1 from top to bottom, the ionization enthalpy decreases. This is primarily due to the increase in atomic size. With each successive element, an additional electron shell is added, resulting in a greater distance between the outermost electron and the nucleus. As a result, the outermost electron experiences weaker attraction to the nucleus, making it easier to remove, and hence, requiring less energy.

2. Trend in Reactivity: The decreasing ionization enthalpy down the group correlates with increasing reactivity. Alkali metals in Group 1 become more reactive as we move down the group since it becomes easier to lose the outermost electron, leading to a more vigorous reaction with water and other substances.

Group 17 (Halogens):

1. Increasing Ionization Enthalpy Down the Group: In contrast to Group 1, the ionization enthalpy increases down Group 17. This is primarily due to the decrease in atomic size and increase in effective nuclear charge as we move down the group. As we move down the group, additional electron shells are added, but there is also an increase in the number of protons in the nucleus. This results in a stronger attraction between the outermost electron and the nucleus, making it more difficult to remove the outermost electron and thus requiring more energy.

2. Trend in Reactivity: The increasing ionization enthalpy down the group correlates with decreasing reactivity. Halogens become less reactive as we move down the group because it becomes more difficult to gain an additional electron to complete the outer electron shell.

Comparison:

• Ionization Enthalpy Trend:

  • Group 1: Decreases down the group.
  • Group 17: Increases down the group.

• Reactivity Trend:

  • Group 1: Increases down the group.
  • Group 17: Decreases down the group.

In summary, Group 1 elements show a decreasing trend in ionization enthalpy and increasing reactivity down the group, while Group 17 elements exhibit an increasing trend in ionization enthalpy and decreasing reactivity down the group. These trends can be explained by changes in atomic size, effective nuclear charge, and electron configuration as we move down the respective groups of the periodic table.