Elements, Isotopes, and the Periodic Table
Elements and organization
What is an element?
An element is a pure substance made of only one kind of atom. Examples include oxygen, carbon, gold, and iron.
Atomic number and mass number
The atomic number is the number of protons in an atom. The mass number is the number of protons plus neutrons, so .
Isotopes
Isotopes are atoms of the same element that have different numbers of neutrons. They have the same atomic number but different mass numbers.
Isotope comparison
| Feature | Same element isotopes | Different elements |
|---|---|---|
| Number of protons | Same | Different |
| Number of neutrons | Can differ | Usually different |
| Chemical identity | Same element | Different element |
Periodic table idea
The periodic table arranges elements in order of atomic number and groups similar elements together.
What is the atomic number?
Atomic number means the number of protons.
Correct answer: Number of protons
What are isotopes?
They are the same element because they have the same number of protons.
Correct answer: Atoms of the same element with different numbers of neutrons
Two isotopes of the same element must have the same number of:
Isotopes are the same element, so they have the same number of protons.
Correct answer: Protons