Valency in chemistry refers to the combining power of an element, which determines how many other atoms it can bond with. It is the number of electrons that an atom can gain, lose, or share in order to achieve a stable electron configuration. Valency is crucial in understanding how elements form compounds and interact with each other to create various chemical reactions. It is represented by a positive or negative integer that indicates the number of bonds an atom can form. **

Yes, nitrogen can change its valency. Nitrogen typically has a valency of 3 or 5, but it can also exhibit valencies of 1, 2, 4, or 6 in certain compounds. This ability to change valency allows nitrogen to form a wide variety of compounds with different elements. **

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The valency of an element is determined by the number of electrons it needs to gain, lose, or share in order to achieve a stable electron configuration. For main group elements, the valency is often equal to the number of electrons in the outermost energy level (valence electrons). Elements tend to gain, lose, or share electrons to achieve a full outer shell, typically with 8 electrons (octet rule), except for hydrogen and helium which follow the duet rule. Transition metals can have variable valencies depending on the oxidation state. **

The valency of Fe2O3 is +3 for iron (Fe) and -2 for oxygen (O). This means that in Fe2O3, there are two iron atoms with a valency of +3 each, and three oxygen atoms with a valency of -2 each. The overall compound is neutral, with the positive and negative charges balancing each other out. **

The valency of hydroxide (OH) is -1. This means that in chemical reactions, the hydroxide ion typically gains one electron to achieve a stable electron configuration. The negative charge on the hydroxide ion is due to the presence of an extra electron, making it an anion. The valency of -1 allows hydroxide to form ionic bonds with positively charged ions to create compounds such as sodium hydroxide (NaOH) or calcium hydroxide (Ca(OH)2). **

The valency of oxygen is 2. This means that oxygen typically forms compounds by gaining two electrons to achieve a stable electron configuration. Oxygen commonly forms compounds such as water (H2O) and carbon dioxide (CO2) by sharing electrons with other elements. **

Valency is calculated by determining the number of electrons an atom needs to gain, lose, or share in order to achieve a stable electron configuration. For main group elements, the valency can be determined by looking at the group number on the periodic table. For transition metals and other elements, the valency can be determined by considering the number of electrons in the outermost shell and the element's tendency to gain or lose electrons. Once the valency is determined, it can be used to predict how an atom will bond with other atoms to form compounds. **