What type of bond exits between an element X with atomic number 12 and Y with atomic number 17?

1. Analyze the question

We need to determine the type of chemical bond formed between element X (atomic number 12) and element Y (atomic number 17).

2. Explain the concept

• Electronic Configuration: To determine the bonding, we first write the electronic configuration of each element to see how many electrons are in their outermost shells (valence electrons).
• Metals vs. Non-metals: • Elements with 1, 2, or 3 valence electrons are typically metals (they lose electrons to become cations). • Elements with 5, 6, or 7 valence electrons are typically non-metals (they gain electrons to become anions).
• Bond Types: • Electrovalent (Ionic) bond: Formed by the complete transfer of electrons from a metal to a non-metal. • Covalent bond: Formed by the sharing of electrons between two non-metals.

3. Show the solution

• Element X (Atomic number 12): • Electronic configuration: $1s^2 2s^2 2p^6 3s^2$ (or 2, 8, 2). • X has 2 valence electrons. It is a metal (Magnesium). It will lose these 2 electrons to achieve a stable octet structure, forming an $X^{2+}$ ion.
• Element Y (Atomic number 17): • Electronic configuration: $1s^2 2s^2 2p^6 3s^2 3p^5$ (or 2, 8, 7). • Y has 7 valence electrons. It is a non-metal (Chlorine). It needs 1 electron to complete its octet, forming a $Y^-$ ion.

The Reaction: Since X is a metal and Y is a non-metal, X will transfer its electrons to Y. Specifically, one atom of X will donate its 2 electrons to two atoms of Y ($XY_2$). This complete transfer of electrons results in an electrovalent (ionic) bond.

4. Identify the answer

The correct option is A.

5. Exam Tip

A simple way to remember this for JAMB: If you see a metal (Group I or II) reacting with a non-metal (Group VI or VII), the bond is almost always Electrovalent/Ionic. If you see two non-metals reacting, it is usually Covalent.