a) Atomic number: -The atomic number of an element is the number of protons present in the nucleus of an atom. It is denoted by Z. For a neutral atom, the number of protons equals the number of electrons.
b) Mass number: -The mass number of an atom is the sum of the number of protons and neutrons present in its nucleus. It is denoted by A.
Formula:
Mass number (A) = Number of protons + Number of neutrons
More Questions on Journey Inside the Atom
1Given two atoms: Atom A has 17 protons, 18 neutrons, and 17 electrons. Atom B has 18 protons, 18 neutrons, and 18 electrons. Which statement is correct?
→ 2An element has a full outermost electron shell. What can be inferred about its chemical reactivity?
→ 3Describe the main limitation of the Bohr model of the atom.
→ 4An element 'X' has 12 electrons. Which of the following elements would it likely form a stable compound with?
→ 5Which experiment demonstrated that atoms contain negatively charged particles called electrons?
→ 6Explain how the existence of isotopes contradicts one of the main postulates of Dalton's atomic theory.
→ 7Consider a neutral atom with an atomic number of 20. If it forms an ion, what would be the most likely charge on this ion?
→ 8Which of the following statements about the arrangement of electrons in shells is consistent with the Bohr-Bury rules?
→ 9Why are some atoms of the same element found to have different mass numbers?
→ 10An element has an electronic configuration of 2, 8, 8, 1. What is its valency, and what type of ion would it form?
→ 11Explain the concept of an electron shell or energy level in the context of atomic structure.
→ 12Which of the following subatomic particles has a mass approximately equal to that of a proton but carries no electrical charge?
→ 13An ion of element Z has a mass number of 32, 16 protons, and a charge of -2. How many neutrons and electrons does this ion have?
→ 14Why was the 'plum pudding' model unable to explain the results of the alpha-particle scattering experiment?
→ 15An atom X has an atomic number of 9 and an atom Y has an atomic number of 11. Describe the type of bond they would most likely form with each other.
→ 16What is the maximum number of electrons that can be held in the outermost shell of an atom, according to the Bohr-Bury scheme, and what is this rule called?
→ 17If an atom has 19 electrons, 19 protons, and 20 neutrons, what is its symbol with mass number and atomic number?
→ 18An element P has 11 electrons and belongs to the 3rd period. What is its valency, and what type of compound would it most likely form with oxygen?
→ 19Which of the following correctly describes the particles found in the nucleus of an atom?
→ 20Explain how the concept of valency helps in writing the chemical formula of ionic compounds.
→ 21Consider a hypothetical atom with 12 protons and 12 neutrons. If this atom undergoes a chemical reaction where it becomes an ion with a -2 charge, how many electrons does this ion possess?
→ 22Why is the Bohr model still used as a simplified representation for teaching atomic structure, despite its limitations?
→ 23An element has 5 electrons in its outermost shell and belongs to the 3rd period. What is its atomic number?
→ 24What was the significance of the "empty space" concept in Rutherford's model of the atom, compared to Thomson's model?
→ 25An element has 13 protons, 14 neutrons, and 10 electrons. What is its atomic number, mass number, and net charge?
→ 26Why are electrons considered to have negligible mass compared to protons and neutrons, even though they are fundamental particles?
→ 27If an element forms an ion with a charge of +2 and has 18 electrons, what is its atomic number?
→ 28What is the maximum number of electrons that can be accommodated in the N-shell (fourth shell) of an atom?
→ 29Describe the main difference in how electrons are depicted in Rutherford's model versus Bohr's model.
→ 30If a neutral atom has 15 protons and its mass number is 31, how many energy shells are occupied by electrons, and how many electrons are in the outermost shell?
→ 31Which of the following pairs are isotopes?
→ 32What role do neutrons play in the stability of atomic nuclei, particularly for heavier elements?
→ 33An element has an atomic number of 16. What will be its electronic configuration, valency, and type of ion formed?
→ 34Explain the primary difference between the atomic number (Z) and the mass number (A) of an atom.
→ 35An atom of element Y has 17 protons and 20 neutrons. What is its mass number and atomic number?
→ 36How do you determine the group and period of an element based on its electronic configuration, assuming it's a main group element?
→ 37If an atom of an element has 19 electrons, what is the maximum number of electrons that can be accommodated in its third shell (M-shell)?
→ 38An atom has an electron configuration of 2, 8, 8. What is its atomic number, and is it likely to be reactive or unreactive?
→ 39Which of the following statements about the Bohr model of the atom is incorrect?
→ 40Describe the main difference between a cation and an anion, including how each is formed.
→ 41Consider an element X that forms an oxide with the formula X2O3. What is the probable electronic configuration of X if it is in the third period?
→ 42Why is the atomic number a more fundamental property for defining an element than the mass number?
→ 43Given a sample of natural neon, which consists of three isotopes: Ne-20 (90.92%), Ne-21 (0.26%), and Ne-22 (8.82%). Explain why the atomic mass of neon is approximately 20.18 amu, and not a whole number.
→ 44An element has electronic configuration 2, 8, 4. What is its group number and period number in the periodic table?
→ 45Why are canal rays deflected towards the negative plate in an electric field?
→ 46An ion has 18 electrons and 17 protons. What is its symbol and charge?
→ 47Contrast the main features of Thomson's atomic model with Rutherford's atomic model.
→ 48An atom has an atomic number 17 and a mass number 35. It forms a compound with hydrogen, with the formula HX. What is the valency of X in this compound?
→ 49How did the limitations of Rutherford's model regarding atomic stability pave the way for Bohr's postulations about electron orbits?
→ 50Explain the concept of valency in terms of an atom's electron configuration.
→ 51Calculate the number of protons, neutrons, and electrons in an iodide ion (I-) with a mass number of 127. The atomic number of iodine (I) is 53.
→ 52Which of the following elements would be expected to be chemically unreactive?
→ 53What experimental evidence led to the conclusion that the nucleus of an atom is positively charged?
→ 54An element has 2 valence electrons and belongs to the 4th period. Write its full electronic configuration.
→ 55Why did Rutherford's model propose that the nucleus is very small and dense compared to the overall size of the atom?
→ 56Describe one major point of agreement and one major point of disagreement between Dalton's atomic theory and modern atomic theory.
→ 57An atom has 10 protons, 10 neutrons, and 10 electrons. If it loses 2 electrons, what will be its net charge, atomic number, and mass number?
→ 58Which subatomic particle was discovered by J.J. Thomson?
→ 59Consider the elements Magnesium (Mg, Z=12) and Calcium (Ca, Z=20). Both are in Group 2 of the periodic table. How do their electron configurations explain their similar chemical properties?
→ 60Explain why the first shell (K-shell) can hold a maximum of 2 electrons, while the second shell (L-shell) can hold up to 8 electrons, according to the Bohr-Bury rules.
→ 61Which experiment provided the first evidence for the existence of a positively charged nucleus within an atom?
→ 62If an element has an atomic number Z and mass number A, how would you determine the number of protons, electrons, and neutrons in a neutral atom of this element?
→ 63An element has an atomic number 13. How many electrons are present in its M-shell (third shell) and what is its valency?
→ 64Why are atoms generally considered to be electrically neutral, despite containing charged subatomic particles?
→ 65Which of the following describes the key difference between isotopes and isobars?
→ 66What was the primary limitation of Thomson's 'plum pudding' model regarding the distribution of positive charge within the atom?
→ 67An element M forms a chloride with the formula MCl2. What is the valency of element M, and what type of ion would it typically form?
→ 68Explain why cathode rays are deflected towards the positive plate in an electric field.
→ 69Two elements, A and B, have mass numbers 40 and 39 respectively. Element A has 20 protons, while element B has 19 protons. What is the relationship between elements A and B?
→ 70Explain why the atomic mass of most elements is not a whole number.
→ 71If an atom has 15 protons and a mass number of 31, how many electrons and neutrons does a neutral atom of this element possess?
→ 72A neutral atom of an element has an electronic configuration of 2, 8, 7. What is its valency and what type of ion is it likely to form?
→ 73Describe the key limitation of Rutherford's atomic model that led to the development of Bohr's model.
→ 74An element has an atomic number of 11. Which of the following is true regarding its ion formation and reactivity?
→ 75Which of the following statements about J.J. Thomson's model of the atom is incorrect?
→ 76Why was the discovery of the neutron by James Chadwick crucial for developing a more complete model of the atom, even after protons and electrons were identified?
→ 77Consider two isotopes of carbon: Carbon-12 and Carbon-14. How do these two isotopes differ in terms of subatomic particles, and what is the implication of this difference for their chemical properties?
→ 78An element X has a valency of 3. What would be the most probable electronic configuration for an atom of this element if it is in the third period?
→ 79Rutherford's alpha-particle scattering experiment led to the rejection of Thomson's model. Explain two significant observations from Rutherford's experiment that contradicted Thomson's 'plum pudding' model.
→ 80Consider an atom with 17 protons, 18 neutrons, and 17 electrons. Which of the following statements accurately describes its atomic characteristics?
→ 81Write the complete symbol for the atom with the given atomic number [Z] & mass number [A].
→ 82How are the isotopes of hydrogen represented?
→ 83An atom contains 3 protons, 3 electrons and 4 neutrons. What is its atomic number, mass number & valency?
→ 84Why does Helium have zero valency?
→ 85From the symbol ³²₁₆S, state: i) Atomic number of sulphur ii) Mass number of sulphur iii) Electronic configuration of sulphur
→ 86Give the symbol, relative charge & mass of the three subatomic particles.
→ 87State the maximum capacity of various shells to accommodate electrons.
→ 88How many electrons are present in the valence shell of nitrogen & argon?
→ 89Which kind of elements have tendency to lose electrons? Give example.
→ 90What are valence electrons? Give example.
→ 91Give one achievement and one limitation of J.J. Thomson's model of atom.
→ 92Identify the isotopes out of A, B, C & D: ³³A₁₇, ⁴⁰B₂₀, ³⁷C₁₇, ³⁹D₁₉
→ 93Write the charges on subatomic particles.
→ 94Name the particles which determine the mass of an atom.
→ 95What are isobars?
→ 96Give the number of protons in ³⁵Cl₁₇.
→ 97What type of charge is present on the nucleus of an atom?
→ 98How many electrons at the maximum can be present in the first shell?
→ 99What was the model of an atom proposed by Thomson?
→ 100How many times is a proton heavier than an electron?
→ 101Which is heavier, neutron or proton?
→ 102Name the scientist and his experiment which proved that the nucleus of an atom is positively charged.
→