The atomic number of oxygen is 8 because oxygen has?
8 protons in the nucleus.
electrons in 8 shells.
a second shell with 8 electrons.
an atomic mass of 8.
The correct answer and explanation is :
The correct answer is: 8 protons in the nucleus.
Explanation:
The atomic number of an element refers to the number of protons in the nucleus of an atom of that element. In the case of oxygen, its atomic number is 8, which means every oxygen atom has 8 protons in its nucleus. This number is what defines the element as oxygen and distinguishes it from other elements on the periodic table.
The number of protons in an atom is also equal to the number of electrons in a neutral atom. Thus, oxygen also has 8 electrons surrounding its nucleus. These electrons are arranged in electron shells (energy levels) around the nucleus. For oxygen, these 8 electrons are arranged in two shells: the first shell contains 2 electrons, and the second shell contains 6 electrons.
To further clarify the incorrect options:
- Electrons in 8 shells: This statement is not correct. Oxygen only has 2 electron shells, not 8. The second shell holds 6 electrons, and the first shell holds 2 electrons.
- A second shell with 8 electrons: While oxygen has 8 electrons in total, only 6 electrons are found in the second shell. The first shell contains 2 electrons. Therefore, this statement is incorrect.
- An atomic mass of 8: This is incorrect as well. The atomic mass (or atomic weight) of oxygen is not exactly 8; it is approximately 16. The atomic mass is the sum of the number of protons and neutrons in an atom’s nucleus. Oxygen’s most common isotope has 8 protons and 8 neutrons, giving it an atomic mass of about 16.
Thus, the defining characteristic of oxygen’s atomic number being 8 comes from the presence of 8 protons in the nucleus, which is the primary determinant of an element’s identity.