Isotopes | Isotopes and ions | High school chemistry | Khan Academy

TL;DR

Elements are defined by their atomic number, but isotopes of elements can have different numbers of neutrons, resulting in different mass numbers.

Transcript

• [Instructor] Every element is defined by the number of protons in its atoms, which is called its atomic number. So for example, every atom of potassium has 19 protons and every atom of cobalt has 27 protons. But what about neutrons? Well, an element doesn't always have the same number of neutrons in its atoms. Atoms of the same element with diffe... Read More

Key Insights

• #️⃣ Atomic number defines an element, while mass number describes an isotope.
• #️⃣ Isotopes have different numbers of neutrons but the same number of protons.
• #️⃣ Mass number is calculated by adding the number of protons and neutrons.

Questions & Answers

Q: What determines an element's atomic number?

An element's atomic number is determined by the number of protons in its atoms. It uniquely identifies the element.

Q: What are isotopes?

Isotopes are atoms of the same element that have different numbers of neutrons. They have the same number of protons but different mass numbers.

Q: How is an isotope's mass number calculated?

An isotope's mass number is calculated by adding the number of protons and neutrons in its atom. It represents the sum of these particles.

Q: How is an isotope represented in notation?

Isotopes can be represented in notation as X-A, where X is the chemical symbol and A is the mass number. For example, carbon-12 is represented as C-12.

Summary & Key Takeaways

• Atoms of the same element can have different numbers of neutrons, resulting in isotopes.

• Isotopes have different mass numbers, which are the sum of the protons and neutrons in the atom.

• Isotope notation is used to represent different isotopes, with the chemical symbol, mass number, and atomic number.