Atomic Structure

To solve this question, we need to determine which of the following sets of atomic numbers corresponds to elements that have similar chemical properties.

1. Elements with Similar Chemical Properties:
Elements with similar chemical properties are typically in the same group (column) of the periodic table. Elements in the same group have the same number of valence electrons, which leads to similar chemical behavior.

2. Evaluating the Options:

• (1) 7, 8, 9 – These correspond to Nitrogen (7), Oxygen (8), and Fluorine (9), which are in different groups (15, 16, and 17), so they do not have similar properties.
• (2) 9, 17, 35 – These correspond to Fluorine (9), Chlorine (17), and Bromine (35). These are all halogens (group 17), so they have similar chemical properties. ✔
• (3) 3, 10, 11 – These correspond to Lithium (3), Neon (10), and Sodium (11). Neon is a noble gas, while Lithium and Sodium are alkali metals, so they do not share similar properties with Neon.
• (4) 10, 11, 12 – These correspond to Neon (10), Sodium (11), and Magnesium (12). Sodium and Magnesium are metals, but Neon is a noble gas, so they do not have similar properties.

Final Answer:
The correct answer is (B) 9, 17, 35, as they are all halogens in group 17.

To solve this question, we need to understand what happens when an electron in an atom moves from a lower energy level (ground state) to a higher energy level (excited state).

1. Electron Transition in an Atom:
When an electron moves from the ground state (lowest energy level) to an excited state (higher energy level), it must gain energy. This energy is typically supplied by absorbing a photon.

2. Key Concept:
Energy is absorbed by the electron to overcome the energy gap between the ground state and the excited state.

3. Evaluating the Options:

• (1) No change in energy – Incorrect; energy must change to change levels.
• (2) Energy is emitted – Incorrect; energy is emitted when electron falls back to a lower level.
• (3) Energy is absorbed – Correct ✔
• (4) Depends on atom – Incorrect; the process is general across all atoms.

Final Answer:
The correct answer is (C) Energy is absorbed.

To solve this problem, we need to follow the order of electron filling based on the Aufbau principle, which tells us the sequence of orbital filling according to increasing energy levels.

1. Electron Configuration Order:
The order of orbital filling is:
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → ...

2. After 3p:
According to the Aufbau principle, after electrons fill the 3p orbital, the next orbital to be filled is 4s — not 3d or 4p.

3. Evaluating the Options:
(A) 4s – Correct ✅
(B) 3d – Incorrect (filled after 4s)
(C) 4f – Incorrect (comes much later)
(D) 4p – Incorrect (comes after 3d)

Final Answer:
The correct option is (A) 4s.

To solve this question, we need to identify which quantum number describes the spatial orientation of orbitals.

1. Types of Quantum Numbers:
- Principal quantum number (n): Indicates the energy level or shell.
- Azimuthal quantum number (ℓ): Describes the shape of the orbital.
- Magnetic quantum number (m_ℓ): Describes the spatial orientation of orbitals in a magnetic field.
- Spin quantum number (m_s): Represents the spin of the electron (either +½ or –½).

2. Correct Quantum Number for Spatial Orientation:
The magnetic quantum number (m_ℓ) defines the orientation of orbitals in space around the nucleus.

Final Answer:
Option (C) m_ℓ is correct.

To solve the problem, we need to identify the element with an electronic configuration similar to .

1. Understanding the Electronic Configuration:
The electronic configuration corresponds to an element with 16 electrons. The number of electrons in an atom is equal to its atomic number. Thus, this element has an atomic number of 16.

2. Identifying the Element with Atomic Number 16:
The element with atomic number 16 is Sulfur (S), which has the electronic configuration . We are asked to find a chemically similar element, which means it must have the same number of electrons in the outermost shell (valence electrons).

3. Verifying the Chemical Similarity:
The elements with 6 valence electrons are Oxygen (O), Sulfur (S), Selenium (Se), and Chlorine (Cl). Among the given options, Oxygen (O) has the same number of valence electrons (6) as the element with electronic configuration .

Final Answer:
The element chemically similar to the given element is .

To solve the problem, we need to identify which pair of atomic numbers corresponds to s-block elements.

1. Understanding s-block Elements:
The s-block elements are those whose outermost electrons are in the s-orbital. These elements are found in the first two groups of the periodic table, which include:

• Group 1: Alkali metals (e.g., lithium, sodium)
• Group 2: Alkaline earth metals (e.g., magnesium, calcium)

2. Identifying the s-block Elements Based on Atomic Numbers:

• Atomic number 5 corresponds to boron (B), which is not an s-block element.
• Atomic number 6 corresponds to carbon (C), which is not an s-block element either.
• Atomic numbers 9 and 10 correspond to fluorine (F) and neon (Ne), which are not s-block elements.
• Atomic numbers 11 and 12 correspond to sodium (Na) and magnesium (Mg), both of which are s-block elements.

Final Answer:
The correct answer is (C) 11, 12.

To solve the problem, we need to determine the maximum number of electrons that can be present in an orbital of an atom.

1. Understanding Orbitals:
Each orbital can hold a maximum of 2 electrons. This is based on the Pauli exclusion principle, which states that no two electrons in the same atom can have the same set of quantum numbers. Therefore, each orbital can accommodate up to 2 electrons with opposite spins.

Final Answer:
The maximum number of electrons present in an orbital of an atom is 2 (Option D).

1. Understanding the Classification Systems:
Various systems have been used to classify elements, but the classification based on the atomic number is a key aspect of the Modern Periodic Table.

• Dobereiner's Law of Triads: This system classified elements into groups of three (triads), where the middle element had an atomic weight approximately equal to the average of the other two. However, this classification was not based on atomic number.
• Newland's Law of Octaves: Newland classified elements based on their atomic masses, where every eighth element shared similar properties. This was also not based on atomic number.
• Mendeleev's Periodic Table: Mendeleev's table was based on atomic masses but laid the foundation for the modern periodic table. It organized elements in a periodic manner and predicted the existence of undiscovered elements, though it did not directly use atomic numbers.
• Modern Periodic Table: The modern periodic table is based on atomic number, where elements are arranged in increasing order of their atomic number. This system fully accounts for the periodic properties of elements and is the one we use today.

2. Conclusion:
The classification based on atomic number is found in the Modern Periodic Table.

Final Answer:
The correct answer is (C) Modern periodic table.