Hydroxide Valency Explained Simply

by Wholesomestory Johnson 35 views

Hello! I am here to help you with your question. The hydroxide valency is a fundamental concept in chemistry. I will provide a clear, detailed, and correct answer to help you understand this important aspect of chemical bonding and reactions.

Correct Answer

The valency of hydroxide (OH-) is 1.

Detailed Explanation

Let's delve into why the valency of hydroxide is 1. This understanding is crucial for predicting how hydroxide ions will interact with other ions and molecules.

Key Concepts

  • Valency: Valency, or valence, represents the combining capacity of an element or a group of atoms. It's the number of chemical bonds an atom or a group of atoms can form with other atoms. This number is often determined by the number of electrons an atom or ion can gain, lose, or share during chemical bond formation.
  • Hydroxide Ion (OH-): Hydroxide is a polyatomic ion composed of one oxygen atom and one hydrogen atom, chemically bonded together, and carrying a negative charge (-1). The hydroxide ion is a crucial component of bases.
  • Chemical Bonds: Chemical bonds are the attractive forces that hold atoms together to form molecules or compounds. There are different types of chemical bonds, including ionic bonds (formed by the transfer of electrons) and covalent bonds (formed by the sharing of electrons).
  • Ions: Ions are atoms or molecules that have gained or lost electrons, giving them an electrical charge. Cations are positively charged ions (formed by losing electrons), while anions are negatively charged ions (formed by gaining electrons).

Understanding Hydroxide's Valency

  1. Formation of Hydroxide: The hydroxide ion (OH-) is formed when a water molecule (H₂O) loses a hydrogen ion (H+). This leaves an oxygen atom bonded to a hydrogen atom, with an extra electron resulting in a negative charge.

    • H₂O → H+ + OH-

  2. Charge and Bonding: The negative charge on the hydroxide ion (-1) arises from the extra electron. This extra electron allows the hydroxide ion to form one chemical bond with a positively charged ion (a cation), or it can participate in other chemical reactions.

  3. Examples of Hydroxide in Compounds:

    • Sodium Hydroxide (NaOH): Sodium (Na) has a valency of +1. It combines with hydroxide (OH-, valency -1) to form sodium hydroxide, a strong base. The formula reflects that one sodium ion bonds with one hydroxide ion.
    • Potassium Hydroxide (KOH): Potassium (K) also has a valency of +1. It forms potassium hydroxide (KOH), another strong base, where potassium and hydroxide combine in a 1:1 ratio.
    • Calcium Hydroxide (Ca(OH)₂): Calcium (Ca) has a valency of +2. Therefore, it combines with two hydroxide ions to form calcium hydroxide. The formula shows that one calcium ion bonds with two hydroxide ions to balance the charges.

  4. Role in Chemical Reactions: Hydroxide ions are very reactive. They are strong nucleophiles (electron-pair donors) and play a crucial role in various chemical reactions, particularly acid-base reactions and nucleophilic substitution reactions.

    • Acid-Base Reactions: Hydroxide ions react with acids to neutralize them. For instance, when hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH), the reaction produces water and sodium chloride (NaCl) or common salt. The hydroxide ion accepts a proton (H+) from the acid, forming water (H₂O).
    • Nucleophilic Substitution: Hydroxide ions are excellent nucleophiles. They attack carbon atoms that are electron-deficient in organic molecules, causing the displacement of leaving groups (like halides).

  5. Why the Valency is 1:

    • Each hydroxide ion carries one negative charge. This single negative charge arises from the extra electron. This extra electron allows the hydroxide to form a single bond with a positive ion to form an electrically neutral compound. This is why its combining capacity, or valency, is 1.

Detailed Examples of Hydroxide Interactions

Let's explore a few detailed examples:

  1. Sodium Hydroxide (NaOH) Formation:

    • Sodium (Na) has one valence electron and tends to lose it to achieve a stable electron configuration.
    • Hydroxide (OH-) has an extra electron, and hence it is ready to accept a positive ion, such as Na+.
    • The sodium ion (Na+) donates its electron to hydroxide, forming an ionic bond with the O of hydroxide resulting in NaOH.

  2. Calcium Hydroxide (Ca(OH)₂) Formation:

    • Calcium (Ca) has two valence electrons and tends to lose them to achieve a stable electron configuration.
    • Calcium (Ca) donates one electron to each of the two hydroxide ions (OH-), forming two ionic bonds resulting in Ca(OH)₂.
    • Thus, calcium hydroxide has two hydroxide ions and one calcium ion, ensuring the charge balance.

  3. Hydroxide in Acid-Base Neutralization:

    • When hydrochloric acid (HCl) is mixed with sodium hydroxide (NaOH):
    • HCl (acid) donates a proton (H+) to the OH- (base) from NaOH.
    • The proton combines with OH- to form water (H₂O).
    • Na+ and Cl- ions remain in the solution as sodium chloride (NaCl), or common salt.
    • This is a clear illustration of how the hydroxide ion (valency -1) reacts with the hydrogen ion (H+) from the acid, neutralizing the acid and forming water and salt.

Key Factors to Remember

  • Hydroxide's valency of 1 is due to its single negative charge.
  • Hydroxide acts as a nucleophile and a base, participating in various chemical reactions.
  • The number of hydroxide ions in a compound depends on the valency of the metal cation. For instance, Ca has +2, therefore you need two OH⁻ ions.

Key Takeaways

  • The valency of hydroxide (OH-) is 1. This indicates it can form one chemical bond.
  • Hydroxide ions carry a -1 charge due to an extra electron.
  • Hydroxide is a crucial component of bases and participates in acid-base reactions and nucleophilic substitutions.
  • The number of hydroxide ions needed to form a compound depends on the valency of the cation.