Depth 1 · 48 s
Count the protons
Every atom in pure gold is the same kind. Water has two kinds. What decides an atom's kind? Count its protons. One kind of atom makes an element, and there are only about 118.
About this video
A ring of pure gold and a glass of water are both made of atoms. But look at the atoms and there is a big difference: every atom in the pure gold is the same kind of atom, while the water has two different kinds.
What makes atoms different kinds is the number of protons in the nucleus. An atom with 1 proton is always hydrogen. An atom with 6 protons is always carbon, one with 8 is always oxygen, and one with 79 is always gold. Change the number of protons and you have a different kind of atom.
A substance made of only one kind of atom is called an element. Gold is an element: all its atoms have 79 protons. Iron is an element, and so is the oxygen gas in the air. Water is not: each tiny particle of water has hydrogen and oxygen in it. Table salt is not either: it has two kinds of atom, sodium and chlorine. Most things around you are made of a few elements joined together or mixed. The idea that each element has its own kind of atom comes from John Dalton, in 1808.
Scientists know about 118 elements. About 90 are found in nature; the rest have only been made in laboratories, often a few atoms at a time, and many fall apart within seconds. It may seem strange that everything comes from so few, but think of the 26 letters of the English alphabet: they are enough to write every word in every book. In the same way, about 90 kinds of atom are enough to make every rock, river, plant and person. This video goes with the lesson Elements: One Kind of Atom in Chemistry Level 1 on Knaph.
This video shows depth 1 of Element.
Learn ElementTranscript
- 0:00A gold ring and a glass of water. Both are made of atoms. But how many kinds?
- 0:08Count the protons in the nucleus. One is hydrogen. Six, carbon. Eight, oxygen. Seventy-nine, gold.
- 0:19A substance with only one kind of atom is an element. Gold is one. Water and salt are not.
- 0:28About 118 elements are known. About 90 are found in nature. The rest were made in laboratories.
- 0:37Twenty-six letters write every English word. About 90 kinds of atom make everything.
- 0:43One kind of atom makes an element.