The question asks for the definition of the atomic number of an element. This is a fundamental concept in chemistry and atomic structure. We need to recall what each subatomic particle signifies in relation to an element's identity.
B) Protons in the nucleus. This is the correct definition of the atomic number. The number of protons uniquely identifies an element.
The mass number of an atom is a fundamental property that describes the total number of nucleons (protons and neutrons) in its nucleus. Electrons, while part of an atom, contribute negligibly to its mass.
Therefore, the mass number is the sum of protons and neutrons.
Correct Option: B) Protons and neutrons
To determine the number of neutrons in an atom, we need to understand the definitions of mass number and atomic number. The mass number represents the total number of protons and neutrons in the nucleus, while the atomic number represents the number of protons.
C) Mass number - Atomic number is the correct formula to calculate the number of neutrons in an atom, as derived from the definitions of mass number and atomic number.
To determine the number of neutrons in an atom, we need to understand the meaning of the atomic number and mass number. The atomic number represents the number of protons, and the mass number represents the total number of protons and neutrons in the nucleus.
Therefore, an atom of Chlorine-35 contains 18 neutrons.
Correct Option: B) 18
To determine the number of protons, neutrons, and electrons in an atom, we need to understand the notation used for isotopes. The notation \(^{A}_{Z}\text{X}\) represents an element X, where A is the mass number and Z is the atomic number. For a neutral atom, the number of protons equals the atomic number, and the number of electrons also equals the atomic number. The number of neutrons is calculated by subtracting the atomic number from the mass number.
Identify the given element and its notation: The element is Sodium-23, represented as \(^{23}\text{Na}\).
Determine the Atomic Number (Z): For Sodium (Na), the atomic number (Z) is always 11. This is a fundamental property of the element and can be found on the periodic table. In the notation \(^{A}_{Z}\text{X}\), if Z is not explicitly written, it is implied by the element symbol. So, for Na, \(Z = 11\).
Calculate the number of Protons: The number of protons is equal to the atomic number (Z).
Number of Protons \( = Z = 11\).
Calculate the number of Electrons: For a neutral atom (which Sodium-23 is, as no charge is indicated), the number of electrons is equal to the number of protons.
Number of Electrons \( = \text{Number of Protons} = 11\).
Determine the Mass Number (A): The mass number (A) is given in the notation as 23. This represents the total number of protons and neutrons in the nucleus.
Mass Number \(A = 23\).
Calculate the number of Neutrons: The number of neutrons is found by subtracting the atomic number (Z) from the mass number (A).
Number of Neutrons \( = A - Z = 23 - 11 = 12\).
Summarize the results:
Protons = 11
Neutrons = 12
Electrons = 11
A) 11, 12, 11. This option correctly lists the number of protons (11), neutrons (12), and electrons (11) for Sodium-23.
The mass number of an atom is defined as the total number of protons and neutrons in its nucleus. This is a fundamental concept in atomic structure.
Correct Option: D) 35