Lithium has an atomic number of 3 and a mass number of 7. What is the number of protons in a lithium atom?

Rationale

Lithium has 3 protons in its atomic structure.

The atomic number of an element, which is 3 for lithium, directly indicates the number of protons present in its nucleus. This fundamental property defines lithium as an element and differentiates it from others in the periodic table.

A (7) YOUR ANSWER

This answer represents the mass number of lithium, which is the total count of protons and neutrons combined. While lithium has a mass number of 7, it does not reflect the number of protons alone, which is specifically determined by the atomic number.

B (4) YOUR ANSWER

Choosing 4 suggests a misunderstanding of the relationship between protons and neutrons. Since lithium has an atomic number of 3, it cannot have 4 protons. In fact, with 4 total nucleons, lithium would not correspond to any known stable isotope.

C (12) YOUR ANSWER

This option incorrectly identifies a number that does not correspond to lithium. Atomic number 12 corresponds to magnesium, not lithium. Lithium's atomic number is 3, which directly indicates its proton count and element identity.

D (3) CORRECT

This is the correct choice, as the atomic number of lithium is indeed 3, indicating that it possesses 3 protons in its nucleus. This essential feature defines lithium and ensures its placement in the periodic table as an alkali metal.

Conclusion

The atomic number of an element is a fundamental characteristic that determines the number of protons within its atomic structure. For lithium, with an atomic number of 3, it contains 3 protons, which distinguishes it from other elements. The incorrect options reflect either confusion about mass number or misidentification of protons for other elements, emphasizing the importance of understanding atomic structure in chemistry.

Lithium has an atomic number of 3 and a mass number of 7. What is the number of protons in a lithium atom?

Lithium has 3 protons in its atomic structure.

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