Periodic Table Explained: Introduction

:In the first video we saw that all the things in the world are made of incredibly tiny particles called atoms. And also that there are 92 different kinds of them. Most things have more than one type of atom in them, but when we do find something containing just one kind of atom, we call it an element. A nugget of gold is an element because it's made of only gold atoms. The atoms are too small to see with our eyes, even using a good microscope, but if we could zoom in with a magnification of a billion times we could see the individual gold atoms. Each kind of atom had a shorthand way of writing it, called its symbol, using either one or two letters. The symbol for gold is Au, taken from the ancient Latin word it, aurum. The symbol Au could refer to either a single gold atom, or the element gold consisting of many gold atoms.Scientists have made a list of all the types of atoms, starting with the lightest, hydrogen, followed by the next lightest, helium. Just heavier than these are lithium and beryllium. We could give each element a number showing its place in this list. Hydrogen's number would be 1 as it is the first in the list, helium's would be 2, and so on. Here are the first 20 elements in the list, starting with the lightest, hydrogen, and going all the way to the heaviest, uranium. Since there are 92 elements in the list, uranium's number must be 92