Test: Atomic Structure - Class 8 MCQ

When an atom gains electrons, it becomes negatively charged and is referred to as an anion, which is essential for understanding ionic bonding.

E. Goldstein identified protons as positively charged particles present in the atom, which helped establish the concept of charge balance within atomic structure.

Dalton's atomic theory states that during chemical reactions, atoms only rearrange themselves by joining together or separating, but they do not change in essence or are created or destroyed.

Atoms remain stable because electrons move in fixed orbits or shells at high speeds, creating a balance between the inward attraction to the nucleus and the outward centrifugal force.

The atomic number, denoted as Z, represents the number of protons in an atom's nucleus, which also equals the number of electrons in a neutral atom.

The energy levels where electrons reside are called energy shells, and each shell has a specific capacity for electrons, governed by the 2n² rule.

The electronic configuration of carbon is 2, 4, indicating that it has 2 electrons in the first shell and 4 electrons in the second shell, necessary for its bonding behavior.

The mass of an electron is approximately 1/1837 of the mass of a hydrogen atom, highlighting the electron's negligible mass in comparison to protons and neutrons.

The mass number (A) is the sum of the number of protons and neutrons in the nucleus, giving insight into the total atomic mass.

A covalent bond is formed when two atoms share electrons, allowing both to achieve a stable electron configuration, which is common among nonmetals.

Valency refers to the number of electrons that an atom needs to gain, lose, or share to achieve a full outer shell, which is crucial for predicting how atoms will bond with each other.

Sodium has one valence electron, making it monovalent, as it can lose one electron to achieve stability during chemical reactions.

Isotopes are variants of the same element that have the same number of protons (atomic number) but differ in the number of neutrons, resulting in different mass numbers.

Bohr described electrons moving in fixed shells around the nucleus, each with a specific energy level, which helps explain the stability of atoms.

An atom is recognized as the fundamental building block of matter that cannot be broken down into smaller units through chemical reactions. This concept is crucial in understanding the nature of matter in the universe.

J.J. Thomson discovered the electron, a negatively charged particle, which was pivotal in advancing our understanding of atomic structure and led to the development of further atomic models.

Rutherford's gold foil experiment revealed that atoms have a dense nucleus where most of the mass and positive charge are concentrated, fundamentally changing the view of atomic structure.

Protons carry a positive charge, which balances the negative charge of electrons in an atom, ensuring electrical neutrality.

Democritus, a Greek philosopher, introduced the concept of atoms, suggesting that everything is composed of indivisible particles. This foundational idea laid the groundwork for modern atomic theory.

Variable valency refers to elements, particularly metals, that can exhibit multiple oxidation states, allowing them to form various compounds, an important concept in chemistry.