What are the possible oxidation numbers of an element if its atomic number is 17?

1. Analyze the Question

The question asks for the possible oxidation numbers of an element with an atomic number of 17. To solve this, we need to determine the electronic configuration of the element and understand how it gains or loses electrons to achieve a stable octet (a full outer shell).

2. Explain the Concept

• Electronic Configuration: The atomic number (Z) of 17 corresponds to the element Chlorine (Cl).
• Distribution: Filling the shells (2, 8, 7), we see that Chlorine has 7 electrons in its outermost shell (valence shell).
• Octet Rule: Atoms generally react to achieve a stable configuration of 8 electrons in their outer shell. • Gaining electrons: Chlorine needs 1 more electron to complete its octet ($7 + 1 = 8$). Gaining an electron results in an oxidation state of -1. • Losing/Sharing electrons: Because Chlorine is a non-metal with 7 valence electrons, it can also share or "lose" its valence electrons in covalent bonding with more electronegative elements (like Oxygen or Fluorine). The maximum positive oxidation state is equal to the number of valence electrons, which is +7.

3. Show the Solution

• Step 1: Write the electronic configuration of the element (Z=17): $1s^2 2s^2 2p^6 3s^2 3p^5$.
• Step 2: Identify the valence electrons: There are $2 + 5 = 7$ electrons in the third shell.
• Step 3: Determine the negative oxidation state: To complete the shell, it gains 1 electron. Oxidation state = -1.
• Step 4: Determine the maximum positive oxidation state: It can involve all 7 valence electrons in bonding. Oxidation state = +7.

Combining these, the possible oxidation numbers for Chlorine are -1 and +7.

4. Identify the Answer

Comparing our result with the given options, we find that Option A matches our calculated values.

5. Exam Tip

For elements in Groups 15, 16, and 17, a quick trick to find the range of oxidation numbers is:

• Negative state: (Group Number - 18)
• Maximum positive state: (Group Number - 10) For Chlorine (Group 17):
• Negative: $17 - 18 = -1$
• Positive: $17 - 10 = +7$