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Isotopes & Ions
Isotopes and Ions
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Atoms are the building blocks of matter, but atoms of the same element are not always identical. Isotopes and ions explain two important ways atoms can differ while still being part of chemistry. Isotopes differ in the number of neutrons, while ions differ in the number of electrons. Understanding them helps explain medical imaging, food nutrition labels, electric currents in solutions, and how salts form.
The identity of an element is set by its number of protons, called the atomic number. Changing neutrons changes the atom's mass but not the element, so it creates an isotope. Changing electrons gives the atom an electric charge, so it creates an ion. Scientists track these changes using symbols, mass number, atomic number, and charge.
Key Facts
- Atomic number = number of protons.
- Mass number = protons + neutrons.
- Neutrons = mass number - atomic number.
- Isotopes are atoms of the same element with different numbers of neutrons.
- Ion charge = protons - electrons.
- Cations are positive ions and anions are negative ions.
Vocabulary
- Isotope
- An isotope is an atom of the same element that has a different number of neutrons.
- Ion
- An ion is an atom or group of atoms that has gained or lost electrons and has an electric charge.
- Atomic number
- The atomic number is the number of protons in the nucleus of an atom.
- Mass number
- The mass number is the total number of protons and neutrons in an atom's nucleus.
- Charge
- Charge is the electrical state of a particle or atom caused by an imbalance between protons and electrons.
Common Mistakes to Avoid
- Changing protons and still calling it the same element is wrong because the number of protons defines the element.
- Using atomic mass instead of mass number to count neutrons is wrong because atomic mass is often a decimal average of many isotopes.
- Thinking isotopes have different charges is wrong because isotopes differ in neutrons, not electrons.
- Forgetting the sign of an ion's charge is wrong because losing electrons makes a positive ion and gaining electrons makes a negative ion.
Practice Questions
- 1 Carbon-14 has 6 protons and a mass number of 14. How many neutrons does it have?
- 2 A magnesium atom has 12 protons and loses 2 electrons. How many electrons does the ion have, and what is its charge?
- 3 Two atoms both have 17 protons. One has 18 neutrons, and the other has 20 neutrons. Explain whether they are different elements, isotopes, or ions.