The increasing order of reactivity among group 1 elements is \(Li\) \(<Na\) \(<K\) \(<Rb\) \(<Cs\)
whereas that among group 17 elements is \(F>Cl>Br>I\) Explain.
whereas that among group 17 elements is \(F>Cl>Br>I\) Explain.
Solution and Explanation
The elements present in group \(1\) have only \(1\) valence electron, which they tend to lose. Group \(17\) elements, on the other hand, need only one electron to attain the noble gas configuration. On moving down group \(1\), the ionization enthalpies decrease. This means that the energy required to lose the valence electron decreases. Thus, reactivity increases on moving down a group. Thus, the increasing order of reactivity among group \(1\) elements is as follows:
\(Li < Na < K < Rb < Cs\)
In group \(17\), as we move down the group from \(Cl\) to \(I\), the electron gain enthalpy becomes less negative i.e., its tendency to gain electrons decreases down group \(17\). Thus, reactivity decreases down a group. The electron gain enthalpy of F is less negative than \(Cl\). Still, it is the most reactive halogen. This is because of its low bond dissociation energy. Thus, the decreasing order of reactivity among group \(17\) elements is as follows:
\(F > Cl > Br > I\)
Top Questions on Periodic Trends In Properties Of Elements
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Concepts Used:
Trends in Periodic Table
The following trend in periodic properties of elements is observed:
Atomic size Trends:
The distance between the centre of the nucleus and the outermost shell of an atom is known as the atomic radius. In a group the atomic size increases due to the addition of shells as we move from one period to another. Across a period the atomic size decreases as the number of shells remain the same while the nuclear charge increases.
Metallic character Trends:
The elements which lose electrons to form cations are known as metals. Metallic character increases as we move down the group because the atomic size increases which lead to easy loss of electrons. On the other hand, it decreases across a period as we move from left to right.
Non-metallic character Trends:
The elements which have a tendency to gain electrons are known as non-metals. The tendency to gain electrons increases on moving across a period due to an increase in the nuclear charge and decrease in the atomic size. Hence, non-metallic character increases across a period.
Ionization potential Trends:
Ionization potential is defined as the amount of energy required to remove an electron from the outermost shell of a gaseous atom and convert it into a positively charged gaseous ion. The periodic properties in terms of ionization potential increase because the atomic size decreases across a period due to increase in the nuclear charge.
Melting Point Trends:
The melting point of an element is basically the energy required to change the state of an element from its solid state to its liquid state. Which essentially implies breaking a few bonds. Thus, higher the stronger the bond between the atoms, higher will be the melting point.