Question

The atomic numbers of elements \(\mathrm{X}, \mathrm{Y}, \mathrm{Z}\) are \(19.21\) and 25 respectively. The number of electrons present in the 'M' shells of these elements follow the order: (a) \(Z>Y>X\) (b) \(X>Y>Z\) (c) \(Z>X>Y\) (d) \(\mathrm{Y}>Z>\mathrm{X}\)

Short answer

(c) \(Z>X>Y\)

Step-by-step solution

Understand the Electron Shell Configuration

The electron shell structure is based on the atomic number, with electrons filling from the closest shell outward. The M shell can hold up to 18 electrons (3s, 3p, 3d subshells). For quick reference, the atomic numbers are - \(X = 19\),- \(Y = 21\),- \(Z = 25\). These values represent the total number of electrons in the neutral atom.

Configure Electrons for Element X

Element X has an atomic number of 19. The electron configuration for 19 electrons is: - K shell: 2 - L shell: 8 - M shell: 8 - N shell: 1 So, in the M shell, element X has 8 electrons.

Configure Electrons for Element Y

Element Y has an atomic number of 21. The electron configuration is: - K shell: 2 - L shell: 8 - M shell: 9 - N shell: 2 Thus, the M shell of element Y contains 9 electrons.

Configure Electrons for Element Z

Element Z has an atomic number of 25. The electron configuration is: - K shell: 2 - L shell: 8 - M shell: 15 This means element Z utilizes 15 electrons in the M shell.

Compare Electrons in M Shells

Now, let's compare the number of electrons in the M shells: - X = 8 - Y = 9 - Z = 15 Hence, the electron order in the M shells is: \(Z>X>Y\).

Key concepts

Atomic Structure

Atoms form the basic building blocks of matter. Understanding the atomic structure is essential to decipher how elements interact and bond. Every atom is composed of a central core named the nucleus, housing protons and neutrons, and an electron cloud surrounding it.
The nucleus is positively charged due to the presence of protons, defined by the atomic number, which also denotes the number of electrons in a neutral atom. Neutrons add mass but no charge. Encircling the nucleus is the electron cloud, where negatively charged electrons orbit in defined paths or shells.
These shells are designated as K, L, M, N, and so forth. Each shell can hold a set number of electrons, governed by the formula \(2n^2\) where \(n\) is the shell number. Understanding this electron arrangement lays the foundation for delving into deeper chemical interactions and behaviors.

Electron Shells

Electron shells represent the specific orbits where electrons reside around an atom's nucleus. Each shell accommodates a specific number of electrons, structured from the innermost shell outward. The configuration begins with the K shell, capable of holding only 2 electrons, followed by the L shell which holds up to 8.
The subsequent shell, denoted as the M shell, can contain as many as 18 electrons. However, filling these shells follows specific energy and stability levels, governed by the Aufbau principle, Hund’s rule, and Pauli exclusion principle.
This orderly filling is key to forming stable electron configurations in atoms. Recognizing the occupation of these shells helps predict chemical properties and reactive behaviors. Such understanding facilitates the comparison of electron configuration across different elements, enabling learners to deduce the unique qualities observed between them.

Periodic Table

The periodic table is more than just a chart; it is a powerful tool that categorizes elements based on atomic number and shared properties. Developed by Dmitri Mendeleev, it organizes elements in rows and columns that reveal recurrent trends or `periodicity` in properties.
The table's layout aligns elements into periods (rows) according to increasing atomic number and into groups (columns) where elements exhibit similar chemical behaviors. This organization stems from shared electron shell patterns and valence electrons, which govern how an element can bond.
By examining the position of an element in the periodic table, one can infer details about its possible electron arrangement and predict its trend in reactivity, atomic size, and ionization energy among other properties. Thus, the periodic table acts as a roadmap for understanding the vast array of chemical interactions and elemental attributes.