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Polarising power refers to the ability of a cation to distort the electron cloud of an anion. This is an important factor because it affects the chemical behavior and bonding of ionic compounds. - For example, the polarising power of \( \mathrm{Li}^{+} \) and \( \mathrm{Mg}^{2+} \) is considerably high. This high polarising power results from their high charge density, which arises from their small ionic radius and the charge on the ion. - High charge density means the cation can strongly attract the electrons of an anion, leading to significant polarization.The polarising effect is similar for \( \mathrm{Li}^{+} \) and \( \mathrm{Mg}^{2+} \), giving rise to similar chemical properties despite each having different charges (i.e., +1 for Li and +2 for Mg). This similarity is part of what constitutes their **diagonal relationship**. Understanding polarising power helps explain the tendency of these cations to form covalent compounds when bonded with large, highly polarizable anions.

Reactivity with water is an important characteristic of metals and affects their usability in various applications. - **Lithium**, when placed in water, reacts to form lithium hydroxide and releases hydrogen gas. This reaction is quite spontaneous and occurs at a moderate tempo. - On the contrary, **Magnesium** behaves differently. It reacts very slowly with water, especially when the water is cold. The reaction can produce magnesium hydroxide and hydrogen gas. This difference in reactivity is attributed to how readily each metal atom can lose its outer electrons to the surrounding water molecules. The disparity in their reactivities highlights another aspect of the diagonal relationship, where despite some similarities, lithium and magnesium may have different chemical behaviors, such as in their interaction with water.

Deliquescence refers to the tendency of a substance to absorb moisture from the air until it dissolves in the absorbed water and forms a solution. - Both \( \mathrm{LiCl} \) (lithium chloride) and \( \mathrm{MgCl}_{2} \) (magnesium chloride) demonstrate this property. They are deliquescent in nature.- This property arises because these compounds can attract and hold water molecules strongly.- **Deliquescence** is a key consideration when storing chemicals like \( \mathrm{LiCl} \) and \( \mathrm{MgCl}_{2} \), as they must be kept in airtight containers to prevent them from absorbing moisture from the air. This property of deliquescence is influenced by their crystal structures and the polarity of the molecules, making them highly efficient at absorbing water vapor from the environment.

Reactions with bromine can differ significantly between elements due to their differing energetic requirements. - **Lithium** reacts fairly readily with bromine even at ordinary temperatures. The reaction forms lithium bromide and is exothermic, releasing heat in the process. - **Magnesium**, however, behaves differently. Magnesium does not react with bromine at ordinary temperatures. For magnesium to react with bromine, heating is often required to surmount the energy barrier. Hence, magnesium does not spontaneously react with liquid bromine at room temperature. This variation in reactivity is important in practical chemistry and influences how these elements are utilized in chemical synthesis and industrial applications. Understanding the reaction conditions required for element interactions with bromine is crucial for safely conducting experiments and in industrial processes where bromine is used as a reactant.