Relative atomic mass of calcium is approximately __________ its atomic number.

(a) Equal

(b) Twice

(c) Thrice

(d) None of these

The relative atomic mass of calcium is approximately (b) Twice its atomic number. Let’s break this down to understand why this is the case.

Understanding Atomic Mass and Atomic Number

To start, it's essential to clarify what we mean by relative atomic mass and atomic number. The atomic number of an element is the number of protons found in the nucleus of its atoms. For calcium, this number is 20. This means that every calcium atom has 20 protons.

Calculating Relative Atomic Mass

The relative atomic mass, on the other hand, is a measure that reflects the average mass of an element's atoms compared to the mass of carbon-12, which is defined as 12 atomic mass units (amu). For calcium, the relative atomic mass is approximately 40.08 amu.

Comparing the Two Values

Now, if we look at the relationship between these two values:

• Atomic number of calcium: 20
• Relative atomic mass of calcium: ~40.08

If we take the atomic mass of calcium (around 40) and divide it by its atomic number (20), we find:

40 / 20 = 2

This calculation shows that the relative atomic mass of calcium is indeed about twice its atomic number.

Why This Matters

This relationship is not unique to calcium; many elements exhibit a similar pattern where their relative atomic mass is roughly double their atomic number. This can be attributed to the fact that most of the mass of an atom comes from its protons and neutrons, and since neutrons are present in roughly equal numbers to protons in many elements, the relative atomic mass often reflects this balance.

Real-World Implications

Understanding these concepts is crucial in fields like chemistry and physics, as they help in predicting how elements will behave in reactions, their stability, and their interactions with other elements. For example, knowing the atomic mass and number can aid in calculating molar masses, which is essential for stoichiometry in chemical equations.

In summary, the answer to your question is that the relative atomic mass of calcium is approximately twice its atomic number, making option (b) the correct choice. This relationship highlights the fundamental principles of atomic structure and mass, which are foundational in the study of chemistry.