Chemistry · Chemical Bonding · NEET
Electrovalency is the number of electrons an atom loses or gains to become an ion. When atoms form an ionic bond, one atom gives electrons and another takes them. The count of electrons moved is the electrovalency. NCERT says it clearly: the electrovalence is equal to the number of unit charges on the ion. So if an ion has a charge of +2, its electrovalency is 2.
Look at the charge on the ion the atom forms. Metals lose electrons to reach the nearest noble gas configuration, and the number lost is the electrovalency. Non-metals gain electrons, and the number gained is the electrovalency. Example: Sodium (Na) loses 1 electron to become Na+, so electrovalency = 1. Calcium loses 2 electrons to become Ca2+, so electrovalency = 2. Chlorine gains 1 electron to become Cl-, so electrovalency = 1. This matters for NEET because it lets you write correct ionic formulas fast.
The number is the same, but the meaning is slightly different. Charge tells you the sign and size (like +2 or -1). Electrovalency is just the size, given as a whole number without the sign. So Ca2+ has a charge of +2 and an electrovalency of 2. Cl- has a charge of -1 and an electrovalency of 1. NCERT calls calcium a positive electrovalence of two and chlorine a negative electrovalence of one, so you can add the sign when needed.
Valency is a general word for the combining power of an atom. Electrovalency is one type of valency, used only for ionic bonds, and it equals the number of electrons transferred. Covalency is another type, used for covalent bonds, and it equals the number of shared electron pairs. So valency is the parent idea, and electrovalency is the ionic version of it.
Calcium has the configuration 2,8,8,2. It has 2 electrons in its outer shell. To reach the stable argon configuration (2,8,8), it must lose both outer electrons, forming Ca2+. Because 2 electrons are lost, its electrovalency is 2. Atoms lose or gain the smallest number of electrons needed to reach a noble gas configuration, which is what fixes the electrovalence number.
Use the electrovalencies to cross-balance the charges. For CaF2: calcium has electrovalency 2 (Ca2+) and fluorine has electrovalency 1 (F-). You need two F- to balance one Ca2+, giving CaF2. This cross-over method (swap the electrovalence numbers as subscripts) gives the correct neutral formula every time, which saves marks in NEET inorganic questions.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Electrovalency is the number of electrons an atom loses or gains to form an ion. Example: in NaCl, sodium loses 1 electron (electrovalency 1) and chlorine gains 1 electron (electrovalency 1).
Aluminium has 3 electrons in its outer shell. It loses all 3 to form Al3+, so its electrovalency is 3.
Yes. Noble gases already have a stable octet, so they do not usually lose or gain electrons. Their electrovalency is taken as zero because they do not form ionic bonds under normal conditions.
Yes. Since it counts whole electrons transferred, electrovalency is always a whole number like 1, 2 or 3, never a fraction.
Metals lose electrons and show positive electrovalency (Na +1, Ca +2). Non-metals gain electrons and show negative electrovalency (Cl -1, O -2).
