Atomic structure is the fundamental concept in chemistry and physics that describes the basic building blocks of matter – atoms. An atom is the smallest unit of an element, and it consists of a nucleus, containing protons and neutrons, surrounded by electrons in energy levels or shells.
MCQs on Atomic structure with answers pdf practice now
1. Nucleus: At the center of an atom lies the nucleus, which is a tiny, dense, and positively charged core. It is composed of protons, which carry a positive charge, and neutrons, which are neutral. The nucleus contributes most of the atom’s mass but occupies only a minuscule fraction of its volume.
2. Electrons: Electrons are negatively charged particles that orbit the nucleus in specific energy levels or electron shells. They are much smaller and lighter than protons and neutrons. Electrons are organized in different energy levels, with the closest level to the nucleus having the lowest energy and the outermost level having the highest energy.
3. Electron Shells: Electrons occupy specific energy levels or electron shells around the nucleus. The innermost shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, and subsequent shells have higher capacities. Electrons fill the shells in a specific order following the “Aufbau principle,” “Pauli exclusion principle,” and “Hund’s rule.”
4. Protons and Atomic Number: The number of protons in an atom’s nucleus defines its elemental identity and is called the “atomic number.” For example, hydrogen atoms have one proton (atomic number 1), carbon atoms have six protons (atomic number 6), and so on.
5. Neutrons and Isotopes: The total number of protons and neutrons in the nucleus is known as the “mass number.” Atoms of the same element can have different numbers of neutrons, resulting in isotopes. Isotopes have the same atomic number (same number of protons) but differ in their mass number.
6. Electrons and Chemical Properties: The arrangement of electrons in an atom’s electron shells influences its chemical properties and reactivity. The outermost shell, known as the valence shell, is particularly important, as it determines how the atom will interact with other atoms to form chemical bonds.
7. Quantum Mechanics: Understanding the behavior of electrons in atoms requires the principles of quantum mechanics. It involves describing electrons as waves and understanding their probabilistic nature in specific regions around the nucleus, known as orbitals.
The study of atomic structure has been crucial in explaining and predicting various chemical and physical properties of matter, as well as in understanding the behavior of atoms in chemical reactions and the formation of molecules.
MCQs on Atomic structure with answers
Q1. What is the smallest unit of an element that retains its chemical properties?
a) Electron
b) Atom
c) Neutron
d) Proton
Q2. Who proposed the plum pudding model of the atom?
a) Niels Bohr
b) Ernest Rutherford
c) J.J. Thomson
d) Max Planck
Q3. Which subatomic particle has a positive charge?
a) Electron
b) Proton
c) Neutron
d) Nucleus
Q4. The atomic number of an element is equal to the number of:
a) Electrons in the nucleus
b) Neutrons in the nucleus
c) Protons in the nucleus
d) Electrons outside the nucleus
Q5. Who developed the planetary model of the atom?
a) Max Planck
b) Niels Bohr
c) Albert Einstein
d) Werner Heisenberg
Q6. The nucleus of an atom is made up of:
a) Protons only
b) Electrons only
c) Protons and electrons
d) Protons and neutrons
Q7. Which of the following particles have negligible mass?
a) Protons and neutrons
b) Electrons and protons
c) Electrons and neutrons
d) Electrons only
Q8. The atomic mass of an atom is primarily determined by the number of:
a) Electrons
b) Protons
c) Neutrons
d) Nucleons
Q9. The number of electrons in a neutral atom is equal to the number of:
a) Protons in the nucleus
b) Neutrons in the nucleus
c) Protons and neutrons combined
d) Protons and electrons combined
Q10. The energy levels of electrons in an atom are also called:
a) Shells
b) Subshells
c) Orbitals
d) Nucleons
Q11. The maximum number of electrons that can occupy the first energy level (K shell) is:
a) 2
b) 4
c) 8
d) 16
Q12. The electron configuration of oxygen (atomic number 8) is:
a) 1s^2
b) 1s^2 2s^2
c) 1s^2 2s^4
d) 1s^2 2s^2 2p^4
Q13. The principal quantum number (n) determines the electron’s:
a) Spin
b) Energy level
c) Shape of the orbital
d) Magnetic quantum number
Q14. How many p orbitals are there in each energy level (shell) of an atom?
a) 1
b) 2
c) 3
d) 4
Q15. The magnetic quantum number (ml) determines the electron’s:
a) Energy level
b) Spin
c) Orientation in space
d) Total angular momentum
Q16. Which of the following subatomic particles is negatively charged?
a) Proton
b) Neutron
c) Electron
d) Nucleus
Q17. The maximum number of electrons that can occupy the third energy level (M shell) is:
a) 2
b) 8
c) 18
d) 32
Q18. Who proposed the quantum mechanical model of the atom?
a) Niels Bohr
b) Albert Einstein
c) Erwin Schrödinger
d) Werner Heisenberg
Q19. An atom with the same number of protons but different numbers of neutrons is called a/an:
a) Isotope
b) Ion
c) Element
d) Molecule
Q20. What is the total number of electrons that can be accommodated in the second energy level (L shell)?
a) 2
b) 8
c) 18
d) 32
Structure of Atom MCQs pdf
Q1. The electron configuration of nitrogen (atomic number 7) is:
a) 1s^2 2s^1
b) 1s^2 2s^2
c) 1s^2 2s^2 2p^1
d) 1s^2 2s^2 2p^3
Q2. The number of electrons in the outermost energy level of an atom is known as its:
a) Atomic number
b) Mass number
c) Valence electrons
d) Isotopes
Q3. The angular quantum number (l) determines the electron’s:
a) Energy level
b) Shape of the orbital
c) Spin
d) Orientation in space
Q4. What is the charge of a nucleus in an atom?
a) Neutral (no charge)
b) Positive
c) Negative
d) Can be either positive or negative
Q5. The concept of quantized energy levels in an atom was first proposed by:
a) Max Planck
b) Ernest Rutherford
c) Niels Bohr
d) J.J. Thomson
Q6. The quantum numbers of an electron in an atom describe its:
a) Speed and position
b) Energy and position
c) Speed and energy
d) Spin and mass
Q7. The electron configuration of carbon (atomic number 6) is:
a) 1s^2
b) 1s^2 2s^2
c) 1s^2 2p^2
d) 1s^2 2s^1 2p^3
Q8. The principle that states that no two electrons in an atom can have the same set of four quantum numbers is known as:
a) Pauli Exclusion Principle
b) Hund’s Rule
c) Aufbau Principle
d) Heisenberg Uncertainty Principle
Q9. An atom that gains or loses electrons and acquires an electric charge is called a/an:
a) Ion
b) Isotope
c) Element
d) Molecule
Q10. The phenomenon of interference of electron waves around the nucleus of an atom is called:
a) Photoelectric effect
b) Wave-particle duality
c) Quantum tunneling
d) Electron diffraction
Q11. Which scientist discovered that the electron has a negative charge?
a) Niels Bohr
b) J.J. Thomson
c) Ernest Rutherford
d) Max Planck
Q12. The quantum mechanical model of the atom is based on:
a) Definite, predictable paths for electrons
b) The concept of stationary orbits
c) The wave nature of electrons
d) The concept of quantized energy levels only
Q13. The Heisenberg Uncertainty Principle states that we cannot know both the exact position and exact ________ of an electron simultaneously.
a) Charge
b) Speed
c) Energy
d) Spin
Q14. The arrangement of elements in the periodic table is based on their:
a) Atomic mass
b) Number of protons
c) Electronegativity
d) Atomic number
Q15. Which of the following elements has the highest atomic number?
a) Helium
b) Neon
c) Argon
d) Krypton
Q16. The modern periodic table consists of how many groups (columns) and periods (rows)?
a) 7 groups and 18 periods
b) 18 groups and 7 periods
c) 7 groups and 7 periods
d) 18 groups and 18 periods
Q17. The element with atomic number 1 is:
a) Hydrogen
b) Helium
c) Lithium
d) Beryllium
Q18. The group/family of elements that contains elements with completely filled electron shells is called the:
a) Alkali metals
b) Halogens
c) Noble gases
d) Transition metals
Q19. An atom with 5 protons, 6 neutrons, and 5 electrons will have a net charge of:
a) -1
b) 0
c) +1
d) +2
Q20. The electron configuration of the alkali metal in Group 1 of the periodic table is usually:
a) ns^2
b) ns^2 np^6
c) ns^2 np^5
d) ns^1
What is an atom?
An atom is the basic unit of matter, comprising a nucleus of protons and neutrons surrounded by electrons in energy levels. It is the smallest particle of an element that retains its chemical properties.
What are electrons?
Electrons are negatively charged particles that orbit the nucleus of an atom. They occupy specific energy levels, determining an atom’s chemical reactivity and bonding behavior.
What is the nucleus?
The nucleus is the central core of an atom, containing protons and neutrons. It contributes most of the atom’s mass and carries a positive charge.
What is atomic number?
Atomic number refers to the number of protons in an atom’s nucleus, defining its elemental identity. Elements with different atomic numbers are unique chemical elements.
What are isotopes?
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons in the nucleus, leading to variations in their atomic masses.