one of more than one hundred pure substances which cannot be chemically broken down, each has its own special number (its atomic number) which is the number of protons in all of its atoms nucleus.
this is a small segment of the periodic table of elements, The video below will show you how to understand the periodic table.
A compound is a thing composed of two or more different elements. It can be similar to a mixture. Which also means it contains two or more seperate atoms.
this is an example of water, which is a compound made up of 2 atoms of hydrogen and one atom of oxygen.
A mixture is made or two or more substances mixed together. There are two different types of mixtures, called homogeneous and heterogeneous.