Aluminium Properties: Understanding Atomic Structure

The question asks us to identify the statement that is NOT correct regarding the element Aluminium (Al), given its atomic number (Z=13) and mass number (A=27). Let's analyze the fundamental properties of an atom.

• Atomic Number (Z): Represents the number of protons in the nucleus of an atom. For a neutral atom, it also equals the number of electrons.
• Mass Number (A): Represents the total number of protons and neutrons in the nucleus.
• Number of Neutrons (N): Calculated as Mass Number minus Atomic Number (N = A - Z).
• Valency: The combining capacity of an element, typically determined by the number of electrons in the outermost shell (valence electrons).

Analyzing Statements for Aluminium (Al)

Given information for Aluminium (Al):

• Atomic Number (Z) = 13
• Mass Number (A) = 27

Statement 1: Number of electrons

The atomic number of Aluminium is 13. In a neutral atom, the number of electrons is equal to the number of protons (which is the atomic number). Therefore, Aluminium has 13 electrons.

Statement: Number of electrons present in Al is 13

Analysis: This statement is correct.

Statement 2: Number of protons

The atomic number (Z) directly defines the number of protons in an atom's nucleus. For Aluminium, Z=13.

Statement: Number of protons present in Al is 13

Analysis: This statement is correct.

Statement 3: Number of neutrons

The number of neutrons is calculated using the mass number (A) and the atomic number (Z).

Formula: N = A - Z

Calculation for Al: N = 27 - 13 = 14. Thus, Aluminium has 14 neutrons.

Statement: Number of neutrons present in Al is 14

Analysis: This statement is correct.

Statement 4: Valency of Aluminium

To determine the valency, we need the electronic configuration of Aluminium.

Electronic Configuration of Al (Z=13): The electrons are distributed in shells as follows: 2 electrons in the first shell (K), 8 electrons in the second shell (L), and 3 electrons in the third shell (M). Configuration: 2, 8, 3.

Valence Electrons: Aluminium has 3 electrons in its outermost shell (M shell). Atoms tend to achieve a stable electron configuration, usually by gaining, losing, or sharing electrons. Aluminium readily loses these 3 valence electrons to form a stable ion with a charge of +3 (Al³⁺).

Valency: The valency of an element is the number of electrons it loses, gains, or shares to form a chemical bond. Since Aluminium loses 3 electrons, its valency is 3.

Statement: The valency of Al is 2

Analysis: This statement is incorrect. The actual valency of Aluminium is 3.

Conclusion

Based on the analysis of each statement:

• Statements 1, 2, and 3 regarding the number of electrons, protons, and neutrons are correct.
• Statement 4 regarding the valency of Aluminium being 2 is incorrect.

Therefore, the statement that is NOT correct is that the valency of Al is 2.