One atom of hydrogen combines with one atom of chlorine and so the valency of chlorine is ……………… .

Answer

To determine the valency of chlorine when it combines with hydrogen, we can follow these steps:

### Step 1: Understand the Electron Configuration
- Hydrogen (H) has 1 electron in its outermost shell.
- Chlorine (Cl) has 7 electrons in its outermost shell.

**Hint:** Remember that the outermost shell of an atom determines its reactivity and how it bonds with other atoms.

### Step 2: Identify the Bonding
- When one atom of hydrogen combines with one atom of chlorine, they form hydrochloric acid (HCl).
- The bond between hydrogen and chlorine is a covalent bond, which means they share electrons.

**Hint:** Covalent bonding involves the sharing of electrons to achieve stability.

### Step 3: Analyze Electron Sharing
- Hydrogen shares its 1 electron with chlorine.
- Chlorine shares 1 of its 7 electrons with hydrogen.

**Hint:** Sharing electrons allows both atoms to achieve a more stable electron configuration.

### Step 4: Determine the Electron Count After Bonding
- After sharing, hydrogen now effectively has 2 electrons (1 from itself and 1 from chlorine).
- Chlorine now effectively has 8 electrons (7 from itself and 1 from hydrogen).

**Hint:** Atoms strive to achieve a full outer shell, similar to the nearest noble gas configuration.

### Step 5: Define Valency
- Valency is defined as the number of electrons an atom needs to gain, lose, or share to achieve a stable electron configuration (noble gas configuration).
- In this case, chlorine needs to share 1 electron to complete its outer shell.

**Hint:** Valency indicates how many bonds an atom can form with other atoms.

### Step 6: Conclude the Valency of Chlorine
- Since chlorine shares 1 electron with hydrogen, its valency is 1.

**Final Answer:** The valency of chlorine is 1.