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We have to study the individual groups of elements in a periodic table in detail to assess their variability in terms of acidity and basicity.
Hydrogen as an element combines with any other element to form hydrides. It can react with both bases and acids to produce hydrides. In such compounds, the hydrogen portrays nucleophilic and basic characteristics. Based on the type of chemical reaction, we come across three different variations of hydrides –ionic hydride, covalent hydride, and metallic hydride.
Ionic hydrides are commonly referred to as saline hydrides. Here, hydrogen is present as an anion, i.e., negatively charged. Chemical reaction to form ionic hydrides takes place with either alkali or alkaline earth metals. However, there are certain exceptions involved here such as the magnesium hydride or MgH2 which expresses a more covalent character. A high temperature is required to conduct these reactions.
Non-metals interact with hydrogen to create covalent hydrides. Feeble Van der Waals force binds the molecules of the concerned electronegative elements in these covalent hydrides. Understandably these compounds are liquids or gaseous with a low melting point. Group 13 elements like gallium, aluminium, and boron form covalent hydrides combined with hydrogen.
Metals and their subsequent alloys which appear in the periodic table also form hydrides with hydrogen atoms. The nature of bonds is ionic forming solid compounds. The chemical nature of these compounds is identical to that of metals. Therefore they are relatively stable at room temperature but react readily with acids at high temperature.
When we study the trend of basicity in the periodic table, all the above-mentioned hydrides shift from left to right with the most acidic compounds towards the right. Ionic hydrides such as NaH appear on the left part while covalent hydrides like HCl are present on the right side of the periodic table.
Basic character trend in periodic table
Electronegativity is an important factor that must be addressed to explain the basic character trend in the periodic table. The basic character of an element decreases with increasing electronegativity.
Electronegativity is described as the inherent atomic tendency to draw electrons. Two main concepts that govern electronegativity are the distance between the charged nucleus and valence shell electrons as well as the nuclear charge number of the element. The measurement of electronegative characteristics is defined on a scale between zero to four. The elements having higher electronegativity appear on the right side of the periodic table. They generally have greater acid strength.
Greater acid strength depends on two factors
High electronegativity of the central element – While analyzing the trend of basicity in the periodic table, we notice elements having higher electronegativity in the right part of the periodic table. The molecules of compounds that are composed of electronegative elements readily dissociate because of increasing electron drift. Electron drift is a chemical phenomenon that takes place when strongly electronegative elements or functional groups dissociate further away from the OH groups. Electrons are drawn towards the strongly electronegative elements which reduce the density of electrons between oxygen and hydrogen.
Greater oxidation number – the primary constituent atom’s oxidation number directly varies with the total number of oxygen bonds with the primary atom. It is evident that oxygen depicts increasing electronegativity, therefore electron drift occurs more vigorously.
Elements forming oxyacids -the trend of basicity in periodic table
Oxyacids are acids with OH functional groups that form bonds with central atomic elements. The OH group is named the hydroxyl group. This hydroxyl group may be linked to additional atoms of oxygen. The oxygen atoms have a higher acidity, thus expectedly they characterize a greater level of electronegativity. The resultant OH group will not be sufficiently polarised. But on the contrary metal atoms show strong basic character. Thus highly polar bonds will be generated between the metal and oxygen atoms. The compound as a whole will depict the basic character in the periodic table.
Conclusion
The trend of basicity in the periodic table decreases vertically along with the columns of the table. Acidity characteristics gradually develop from left to right. It is necessary to discuss the basic and acid characteristics of a compound to assess the subsequent basicity of its constituent atoms.
