RRB Group D Science Structure of Atom By PW Muskan Mam
Understanding the RRB Group D Science Structure of Atom By Muskan Mam is essential for building a strong foundation in chemistry for competitive exams. Questions from atomic structure are frequently asked in RRB Group D, making it a high-weightage topic for scoring marks.
This topic covers important concepts such as electronic configuration, valency, chemical bonding, and atomic properties. It also helps in understanding how elements behave, combine, and form compounds. By learning these basics clearly, candidates can easily solve both conceptual and direct questions in the exam.
What is Atom?
An atom is the smallest part of an element that still shows its chemical behavior. It serves as the fundamental unit of matter and cannot be broken down further through normal chemical processes.
An atom consists of three main subatomic particles: Protons, Neutrons, and Electrons. Protons and neutrons are present in the nucleus at the center of the atom, while electrons revolve around the nucleus in specific energy levels or shells.
Although atoms are extremely small, they combine with other atoms to form molecules, which can exist independently and make up all substances around us.
Structure of Atom
Understanding the structure of an atom is fundamental to comprehending chemistry and physics. This foundational knowledge is important for competitive exams like RRB Group D, as it underpins many chemical reactions and material properties.
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Electronic Configuration and Valency
An element with an electronic configuration of 2, 8, and 7 has 7 valence electrons in its outermost shell. According to the Octet Rule, an atom strives to achieve 8 electrons in its outermost shell for stability. To achieve this, the element will accept one electron. Therefore, its valency is 1, not 7.
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Electronic Configuration and Group Number
An element with electronic configuration 2, 8, 3 has a total of 13 electrons (2+8+3 = 13), indicating its atomic number, which corresponds to Aluminum. In the periodic table, the number of electrons in the last shell (3) often indicates the last digit of the group number. Thus, the element belongs to Group 13.
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Smallest Particle with Independent Existence
An atom typically cannot exist independently; it tends to combine with other atoms. A molecule is formed when two or more atoms combine, and it is the molecule that can exist independently.
|
Particle |
Independent Existence |
Example |
|---|---|---|
|
Atom |
Cannot exist independently |
Individual O, Cl, H |
|
Molecule |
Can exist independently |
O₂, Cl₂, H₂ |
4. Number of Atoms in Sodium Carbonate
The chemical formula for Sodium Carbonate is Na₂CO₃. To calculate the total number of atoms:
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Sodium (Na): 2 atoms
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Carbon (C): 1 atom
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Oxygen (O): 3 atoms
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Total: 2 + 1 + 3 = 6 atoms.
Note: Washing Soda has the formula Na₂CO₃·10H₂O.
5. Types of Chemical Bonds and Maximum Covalent Bonds
A covalent bond is formed by the sharing of electrons between atoms. An ionic bond is formed by the transfer of electrons from one atom to another. For example, Nitrogen can form a maximum of three covalent bonds.
|
Bond Type |
Electron Interaction |
|---|---|
|
Covalent Bond |
Involves electron sharing |
|
Ionic Bond |
Involves electron transfer |
6. Atomicity of Phosphorus
Atomicity refers to the number of atoms present in a single molecule of an element. Phosphorus (P) commonly exists as a molecule with four atoms, represented as P₄. Therefore, the atomicity of Phosphorus is 4.
7. Neutron Presence in Atoms
Neutrons are constituents of most atomic nuclei. However, Hydrogen (specifically its most common isotope, Protium, ¹H) typically contains no neutrons.
8. Dating Fossils Using Isotopes
The process of dating ancient materials, such as fossils, is known as Carbon Dating. This method utilizes Carbon-14 (C14), which is an isotope of Carbon. Isotopes are atoms of the same element (meaning they have the same atomic number) but possess different atomic mass. For example, Carbon-14 has a different atomic mass than the more common Carbon-12.
9. Valence Power and Valency
The valence power, or combining capacity, of an element—which dictates its ability to form chemical bonds—is known as its valency.
10. Charge and Discovery of Electron
The electron carries a negative charge. The magnitude of this charge is 1.6 x 10⁻¹⁹ Coulomb. A proton has the same magnitude of charge but is positive. The electron was discovered by J.J. Thomson, who also proposed the Plum Pudding Model, also known as the Watermelon Model, for the atom.
11. Periodicity in the Periodic Table
The periodic table is organized based on the periodicity of elemental properties, meaning properties generally show regular trends (increasing or decreasing) across periods and down groups.
|
Periodic Properties |
Non-Periodic Property |
|---|---|
|
Electron positivity |
Neutron-Proton (n/p) ratio |
|
Atomic size |
|
|
Electron affinity |
12. Properties of Covalently Bonded Molecules
Covalent bonds involve electron sharing between atoms. This type of bonding results in weak intermolecular forces (forces between molecules). Because these intermolecular forces are weak, relatively less energy is required to overcome them, leading to low melting points and low boiling points for covalently bonded molecules.
13. Maximum Electrons in an Energy Shell
The maximum number of electrons that can be accommodated in any given energy shell, denoted by n, is calculated using the formula 2n². For the fourth energy shell (n=4): 2 * (4)² = 2 * 16 = 32 electrons.
14. Atomicity of Sulfur
Sulfur typically exists as an S₈ molecule, indicating it is polyatomic. Therefore, the atomicity of Sulfur is 8.
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