Problem 25 - Chemistry: The Central Science

Question

(a) Define atomic number and mass number. (b) Which of these can vary without changing the identity of the element?

Step-by-Step Solution

Answer

(a) The atomic number (Z) is the number of protons in the nucleus of an atom, which determines its chemical properties and position in the periodic table. The mass number (A) is the total number of protons and neutrons in the nucleus of an atom, representing its mass. (b) The mass number can vary without changing the identity of the element, as it depends on the number of neutrons in the nucleus. Changing the atomic number would result in a different element.

Step 1: Atomic number definition

The atomic number, represented by the symbol Z, is the number of protons in the nucleus of an atom. It determines the chemical properties of an element and its place in the periodic table.

Step 2: Mass number definition

The mass number, represented by the symbol A, is the total number of protons and neutrons in the nucleus of an atom. It is an integer and represents the mass of an atom or isotope. Step 2: Determine which property can vary without changing the identity of the element

Step 3: Variation in atomic number

The atomic number is responsible for defining an element and its properties. Changing the atomic number means changing the number of protons in the nucleus, which will result in a different element.

Step 4: Variation in mass number

The mass number can vary without changing the identity of an element since it depends on the number of neutrons in the nucleus. Atoms with the same atomic number but different mass numbers are called isotopes of the same element. Changing the number of neutrons does not change the chemical properties of an element, only its mass. #Conclusion# The mass number can vary without changing the identity of the element while the atomic number cannot.