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50 JAMB, WAEC & NABTEB Chemistry Questions on Atomic Structure and Dalton’s Theory (With Answers)

This set of objective questions covers the modifications of Dalton’s atomic theory, the discovery of subatomic particles (protons, neutrons, and electrons), electronic configuration of the first 20 elements, atomic number and mass number calculations, and the concept of isotopy. Based on standard examination content from JAMB, WAEC, and NABTEB, these questions test a thorough understanding of atomic structure and relative atomic mass determination.

Here is another question – WAEC, JAMB & NECO Chemistry Questions on Introduction to Chemistry

Chemistry Questions on Atomic Structure and Dalton’s Theory (With Answers)

Dalton’s atomic theory stated that all elements are made up of small indivisible particles called atoms. This was corrected by Rutherford who discovered that the atom
A. is a solid indivisible piece
B. contains only protons and electrons
C. is made up of protons, neutrons, and electrons
D. cannot be split in a nuclear reaction
According to the passage, Dalton’s statement that “the atom can neither be created nor destroyed” is still plausible only for
A. nuclear reactions
B. ordinary chemical reactions
C. fission of uranium-235
D. formation of organic compounds
In a nuclear reaction such as the fission of uranium-235, the nucleus absorbs a neutron and
A. remains unchanged
B. forms a heavier atom
C. breaks up into fragments forming simpler atoms
D. releases only electrons
The discovery that contradicts Dalton’s statement that “atoms of the same element are alike in every aspect” is the discovery of
A. electrons
B. protons
C. isotopes
D. neutrons
Chlorine has two isotopes which differ in their
A. number of protons and chemical properties
B. neutron content and relative atomic masses
C. electron configuration and atomic number
D. physical and chemical properties
Dalton’s statement that atoms combine in simple whole number ratios to form compounds is not plausible for
A. inorganic compounds with few atoms
B. water and carbon dioxide
C. organic molecules such as proteins, fats, and starch
D. simple binary compounds
Which of the following is an exception to the simple whole number ratio rule even though it is an inorganic compound?
A. Sodium chloride
B. Silicon forming complex trioxosilicates
C. Carbon dioxide
D. Ammonia
The three fundamental particles in an atom are
A. proton, nucleon, electron
B. proton, nucleon, neutron
C. proton, neutron, nucleus
D. proton, neutron, electron
The positively charged particles in an atom having equal mass as the atom of hydrogen are the
A. electrons
B. protons
C. neutrons
D. nucleons
The electron is
A. positively charged and equal in magnitude to the proton
B. negatively charged and opposite in sign to the proton
C. neutral with mass equal to the proton
D. located inside the nucleus
The particle in the atom that has no electrical charge and a mass equal to that of the proton is the
A. electron
B. positron
C. neutron
D. alpha particle
According to Lord Rutherford’s nuclear theory, the nucleus of the atom is made up of
A. protons and electrons
B. neutrons and electrons
C. protons and neutrons
D. protons, neutrons, and electrons
The nucleus of an atom is described as
A. negatively charged and located in the orbitals
B. centrally positioned and positively charged
C. neutral and surrounded by protons
D. located at the edge of the atom
According to Niels Bohr, electrons revolve around the nucleus in circular paths called
A. orbits or shells
B. energy levels or fields
C. electron clouds
D. quantum zones
The shell nearest to the nucleus is denoted by the letter
A. L
B. M
C. K
D. N
The maximum number of electrons that can be accommodated in the K shell is
A. 8
B. 18
C. 2
D. 32
Using the formula 2n², the maximum number of electrons in the L shell (n=2) is
A. 2
B. 8
C. 18
D. 32
The M shell can hold a maximum of 18 electrons, but in the basic electronic configuration of the first 20 elements, it usually holds up to
A. 2 electrons
B. 8 electrons
C. 18 electrons
D. 32 electrons
What is the electronic configuration of an atom of Neon (atomic number 10)?
A. 2, 8, 1
B. 2, 8
C. 2, 6
D. 2, 8, 2
Which of the following atoms contains the highest number of electrons in the outermost shell?
A. Oxygen (₈O)
B. Neon (₁₀Ne)
C. Phosphorus (₁₅P)
D. Potassium (₁₉K)
The number of electrons in the outermost shell of an atom of Sulphur (atomic number 16) is
A. 2
B. 4
C. 6
D. 8
The electronic configuration of Calcium (atomic number 20) is
A. 2, 8, 8, 2
B. 2, 8, 10
C. 2, 8, 18
D. 2, 8, 8, 1
The atomic number of an element is defined as the number of
A. protons in the nucleus of an atom
B. neutrons in the nucleus
C. electrons in the outermost shell
D. protons and neutrons combined
In a neutral atom, the number of protons is equal to the number of
A. neutrons
B. nucleons
C. electrons
D. isotopes
The relative atomic mass of an element is usually not a whole number because
A. atoms contain fractional protons
B. an element consists of two or more isotopes
C. electrons have variable mass
D. the mass spectrometer is inaccurate
The atomic number of an element determines the
A. mass of the atom
B. nature of the atom and distinguishes it from other elements
C. number of neutrons only
D. physical state of the element
Given the symbol ₉F¹⁹, the number of protons in the atom is
A. 9
B. 10
C. 19
D. 28
An element with atomic number 11 and mass number 23 contains
A. 11 protons and 12 neutrons
B. 12 protons and 11 neutrons
C. 11 protons and 23 neutrons
D. 23 protons and 11 neutrons
What is the atomic number of an element whose cation Y⁺ has the electronic configuration 1s² 2s² 2p⁶?
A. 9
B. 10
C. 11
D. 12
The mass number of an atom is the sum of its
A. electrons and protons
B. protons and neutrons
C. electrons, protons, and neutrons
D. valence electrons
An atom with 17 protons, 17 electrons, and 18 neutrons has a mass number of
A. 17
B. 18
C. 34
D. 35
The mass number is also referred to as the
A. atomic number
B. nucleon number
C. proton number
D. electron number
Find the number of neutrons in an atom represented by ₂₁X⁴⁵.
A. 21
B. 24
C. 45
D. 66
The mass of an element is 27 and its atomic number is 13. What is the composition of the nucleus of its atom?
A. 13 electrons and 14 protons
B. 13 neutrons and 14 protons
C. 13 protons and 14 neutrons
D. 13 electrons and 14 neutrons
Isotopy is the phenomenon whereby atoms of an element exhibit
A. different atomic numbers but same mass number
B. different mass numbers but same atomic number
C. different chemical properties
D. same number of neutrons
Isotopes of an element have different physical properties but exhibit the same chemical properties due to differences in the number of
A. protons
B. electrons
C. neutrons
D. positrons
The instrument used to determine the different isotopes present in an element is the
A. mass spectrometer
B. cathode ray tube
C. Geiger Muller counter
D. eudiometer
The isotopes of chlorine are ₁₇Cl³⁵ and ₁₇Cl³⁷ with relative abundances of 75% and 25% respectively. The relative atomic mass of chlorine is
A. 35.0
B. 35.5
C. 36.0
D. 37.0
An element X has two isotopes ₁₀X²⁰ and ₁₀X²² in the ratio of 1:3. The relative atomic mass of X is
A. 20.5
B. 21.0
C. 21.5
D. 22.0
An element with relative atomic mass 16.2 contains two isotopes; ₈X¹⁶ with relative abundance of 90% and ₈Xᵐ with relative abundance of 10%. The value of m is
A. 16
B. 17
C. 18
D. 19
Isotopes of a given element have the same
A. mass number
B. number of neutrons
C. atomic number and chemical properties
D. physical properties
Which of the following elements exhibits isotopy?
A. Sodium
B. Carbon
C. Aluminium
D. Phosphorus
The relative atomic mass of an element is defined as the number of times the average mass of one atom of the element is heavier than
A. one atom of hydrogen
B. one-twelfth of the mass of one atom of carbon-12
C. one atom of oxygen-16
D. the mass of a proton
The mass spectrometer is used to measure the mass of
A. an atom
B. an electron
C. a proton
D. a neutron
Consider an atom represented by ₁₉K⁴⁰. How many neutrons are present in the nucleus?
A. 19
B. 20
C. 21
D. 40
An element Y has atomic number 15 and mass number 31. The number of electrons in a neutral atom of Y is
A. 15
B. 16
C. 31
D. 46
The electronic configuration of Argon (atomic number 18) is
A. 2, 8, 8
B. 2, 8, 18
C. 2, 8, 8, 2
D. 2, 8, 8, 1
Which of the following atoms has a completely filled outermost shell (octet configuration)?
A. Sodium (₁₁Na)
B. Magnesium (₁₂Mg)
C. Chlorine (₁₇Cl)
D. Neon (₁₀Ne)
The electronic configuration of an atom with atomic number 12 is
A. 2, 8, 2
B. 2, 8, 1
C. 2, 10
D. 2, 8, 8, 2
The mass number of an atom is 23 and its atomic number is 11. The number of electrons in the neutral atom is
A. 11
B. 12
C. 23
D. 34