Final answer:
The claim that oxygen-18 has 18 protons is false; oxygen-18 has 8 protons and 10 neutrons. Isotopes differ in the number of neutrons, not protons, which are constant within an element.
Step-by-step explanation:
The statement that oxygen-18 has 18 protons is false. The atomic number of oxygen is 8, which means that every oxygen atom, no matter the isotope, has 8 protons. The difference between isotopes of the same element is the number of neutrons. An oxygen atom with a mass number of 16 (oxygen-16) has 8 neutrons, oxygen with a mass number of 17 (oxygen-17) has 9 neutrons, and oxygen with a mass number of 18 (oxygen-18) has 10 neutrons. Therefore, in terms of protons and neutrons, oxygen-18 has 8 protons and 10 neutrons.
Complete symbols for the atoms in question would be:
- Oxygen-16: ⁸₁⁶O (8 protons, 8 neutrons)
- Potassium: ⁹₁⁹⁹K (19 protons, 20 neutrons)
- Lithium: ³⁷Li (3 protons, 4 neutrons)
In nature, isotopes of elements have a certain natural abundance, with oxygen-16 being the most common isotope of oxygen. The isotopes of chlorine, for example, have different abundances as well, with chlorine-35 (18 neutrons) being more common than chlorine-37 (20 neutrons).
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