Problem 24 - A Complete Resource Book in Chemistry for JEE Main

Question

In ground state, an element has 13 electrons in its \(\mathrm{M}\) shell. The element is (a) copper (b) iron (c) nickel (d) chromium

Step-by-Step Solution

Answer

The element is none of the options provided. It is likely a conceptual check error.

Step 1: Understand Electron Shells and the M Shell

Each electron shell is numbered outward from the nucleus and can hold a specific number of electrons. The sequence is K (2 electrons), L (8 electrons), M (18 electrons). So, the M shell can hold up to 18 electrons.

Step 2: Recognize the Electron Configuration

An element with electrons in its M shell will have filled the K and L shells prior (K = 2 electrons, L = 8 electrons). Thus, it has at least 2 + 8 = 10 electrons in the first two shells before adding to the M shell.

Step 3: Calculate Total Electrons in the Element

If the M shell has 13 electrons, add these to the 10 electrons from the K and L shells: 10 + 13 = 23 total electrons.

Step 4: Determine the Element by Atomic Number

The number of electrons in a neutral atom equals the atomic number. An element with 23 electrons is vanadium, not one of the options given (copper, iron, nickel, chromium). Upon re-evaluating options, none correctly reflect 23 electrons.

Step 5: Verify Problem or Interpret Error

Since the electronic configuration including a filled M shell with 13 electrons requires knowing specific configurations such as sub-levels (e.g., 3d, 4s), review interpretations against typical misconceptions or misprints.

Key Concepts

Electron Shells

Electron shells are the layers or orbitals around an atom's nucleus where electrons reside. Each shell can only hold a certain number of electrons. For instance:

• The K shell is the closest to the nucleus and can hold up to 2 electrons.
• The L shell, which is the second shell, accommodates up to 8 electrons.
• The M shell, being the third shell, can hold a total of 18 electrons.

Understanding how these shells fill up is crucial in determining the electron configuration of an element. Electrons fill the shells starting from the one closest to the nucleus and move outward. This helps in predicting how an element will interact chemically since the electrons in the outermost shell are typically involved in reactions.

Atomic Number

The atomic number is a fundamental concept in chemistry and represents the number of protons in the nucleus of an atom. In a neutral atom, the atomic number also equals the number of electrons. This number is crucial for identifying elements on the periodic table. For instance, if an element has 23 electrons, its atomic number is 23. This helps in determining the element's identity, as each element has a unique atomic number.

Understanding atomic numbers allows chemists to interpret the element's place in the periodic table, predict chemical behavior, and comprehend how elements combine to form compounds. Atomic numbers are key in understanding electron configurations, as they tell you the total number of electrons to place in orbitals.

Chemical Elements

Chemical elements are pure substances consisting of only one type of atom, characterized by their atomic numbers. In the periodic table, elements are ordered by increasing atomic numbers, and each has a unique chemical symbol and properties.

• Chemical elements are classified into groups based on similar properties, such as metals, non-metals, and metalloids.
• Each element exhibits different oxidation states, affecting how they form compounds.
• The periodic table helps predict the characteristics and chemical reactions of elements.

Understanding the basic structure and properties of chemical elements is essential. Recognizing the electron configurations tied to these elements further explains how they behave in nature and in reactions. Elements' reactions are primarily dictated by the electrons in the outermost shells.