The number of electrons in an atom of an element is equal to its: (A) Atomic weight (B) Atomic number (C) Equivalent weight (D) Electron affinity
Hint :The number of electrons in an atom of an element is equal to the number of protons in the atom. With this information, and definitions for each of the above options, the answer can be found.
Complete Step By Step Answer: Option (A) atomic weight is the total weight of the atom, which includes the weight of the protons and neutrons and the little extra weight of electrons as well. With this definition, we can rule out options (A). Option (C) equivalent weight is defined as the quantity of a substance that exactly reacts with, or is equal to the combining value of, an arbitrary fixed quantity of another substance in a particular reaction. This concept has been displaced by the concept of molar mass. With this definition, option (C) can also be ruled out. Option (D) electron affinity is defined as the potential energy change or the amount of energy released when an electron is added to a neutral gaseous atom, forming an anion. It depends on the atomic size, effective nuclear charge, and reactivity of elements as well. With this definition, option (D) can also be ruled out. Option (B) atomic number of a chemical element is defined as the number of protons found in the nucleus of every atom of that element. It uniquely identifies the element. Therefore, since the number of protons in an element is equal to the number of electrons – option (D) is the correct answer. The number of electrons in an atom of an element is equal to its atomic number.
Additional Information: The elements in the periodic table have been arranged according to their atomic number. For example, an atom of the element iron has 26 protons in its nucleus, which implies that it has 26 electrons. Therefore, its atomic number is also 26 in the periodic table.
Note : Such questions can be tricky and require you to know the definitions of such terms. However, having basic knowledge of the periodic table and the characteristics of elements will help you answer this. Atomic number is an important concept to learn and is significant in understanding the trends of the periodic table and later in chemical reactions as well.