An element having the atomic number 17 will resemble which of the following elements having atomic number as given below?

1. Analyze the Question

The question asks us to identify which element (given by its atomic number) shares similar chemical properties with an element that has an atomic number of 17.

2. Explain the Concept

In chemistry, elements in the same group (vertical column) of the Periodic Table exhibit similar chemical properties because they have the same number of valence electrons (electrons in their outermost shell).

• Step 1: Determine the electronic configuration of the element with atomic number 17.
• Step 2: Identify its group.
• Step 3: Determine the electronic configuration of the options provided to see which one falls into the same group.

3. Show the Solution

Step 1: Electronic configuration of atomic number 17 (Chlorine)

• Configuration: $1s^2 2s^2 2p^6 3s^2 3p^5$
• Valence electrons: $2 + 5 = 7$
• This element is in Group 7 (the Halogens). Elements in this group have 7 valence electrons and tend to gain one electron to achieve a stable octet.

Step 2: Check the options for the same valence electron count

• Option A (33): $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^3$. Valence electrons = 5. (Group 5)
• Option B (35): $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^5$. Valence electrons = 7. (Group 7)
• Option C (18): $1s^2 2s^2 2p^6 3s^2 3p^6$. Valence electrons = 8. (Group 0/8 - Noble Gas)
• Option D (19): $1s^2 2s^2 2p^6 3s^2 3p^6 4s^1$. Valence electrons = 1. (Group 1 - Alkali Metal)

Step 3: Compare Since atomic number 35 also has 7 valence electrons in its outermost shell ($4s^2 4p^5$), it belongs to the same group as atomic number 17. Therefore, they will exhibit similar chemical properties.

4. Identify the Answer

The element with atomic number 35 (Bromine) is in the same group as the element with atomic number 17 (Chlorine). Both are halogens.

5. Exam Tip

To quickly find the group of an element, look at the last number in its shell configuration (e.g., 2, 8, 7). If the last number is 1, 2, or 3, it's a metal. If it's 5, 6, or 7, it's a non-metal. Elements in the same group always have the same number of valence electrons!