Theodore Gray - The Kids Book of the Elements: An Awesome Introduction to Every Known Atom in the Universe

WHY IS THE periodic table shaped the way it is? Its not a random coincidence, and its not because it looks pretty this way. The shape of the periodic table is determined by the arrangement of electrons in the atoms of each element.

Atoms are made up of three types of subatomic particles, called protons, neutrons, and electrons. Every atom of a given element has the same number of protons in its nucleus, which is called that elements atomic number. For example, every oxygen atom has 8 protons in its nucleus, so the atomic number of oxygen is 8. Each atom also contains multiple neutrons, but this number isnt always the same for every atom of a given element. In orbit around the nucleus, you will find a number of electrons equal to the number of protons in the nucleus.

Reading in rows from left to right and top to bottom (sometimes with gaps in the rows), the periodic table lists the elements in order of their atomic numbers. The first row has a huge gap between hydrogen (1) and helium (2), then there are progressively smaller gaps as you go down. This might seem random, but it isnt. The gaps are there so the elements in each column share the same number of outer shell electrons, which are the electrons that participate in chemical bonding and thus determine the chemical properties of the elements in that column. Each column, or set of neighboring columns, forms a group of elements that behave in similar ways. Lets take a look at these groups.

THE FIRST GROUP of elements, the leftmost column, is called the alkali metals. The main shared property of the alkali metals is that they are fun to throw in a lake. This is because when you put an alkali metal, such as sodium (11), in water, you get a nice big explosion. I say it