The Kid's Book of the Elements

What Is the Periodic Table of the Elements?

THE PERIODIC TABLE is the universal catalog of the elements. It’s a list of the building blocks that make up everything in the world that you can drop on your foot. (There are some things, such as light, love, logic, and time, that are not in the periodic table. But you can’t drop any of those things on your foot.)

Earth, this book, your foot—everything in the world you can touch—is made of elements. Your foot, for example, is made mostly of oxygen with quite a bit of carbon and hydrogen joining in. Earth is made up of four main elements: iron, oxygen, silicon, and magnesium. This book is made mostly of carbon, oxygen, and hydrogen.

And this is only the beginning! In this book we’ll look at all 118 elements of the periodic table.

A Visual Exploration of Every Known Atom in the Universe

Photographs show samples of the pure or nearly pure element except as follows: At, Rn, Fr, Ac, Pa, and Np show radioactive minerals containing minute traces of the element. Po, Ra, Pm, Pu, and Am show artificial objects containing invisible amounts of the element. Technetium shows a Tc-99 bone scan. Hydrogen shows a Hubble Space Telescope image of the Eagle Nebula, which is mostly hydrogen. 96-118 show the person or place after which the element is named.

The Shape of the Periodic Table

WHY IS THE periodic table shaped the way it is? It’s not a random coincidence, and it’s 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 element’s 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 isn’t 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 isn’t. 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. Let’s 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 can be fun because it depends on whether or not you do it right. The result can be either thrilling or really dangerous. Chemistry is a bit like that: powerful enough to do great things in the world, but also dangerous enough to do terrible things. If you don’t respect the power of chemistry, it will bite you.

Elements in the second group are called the alkali earth metals. They are similar to their neighbors the alkali metals, but not nearly as explosive. When you throw them into water, they react more calmly and slowly.

THE BIG GROUP of elements that takes up the wide middle part of the periodic table is called the transitional metals. When you think of metal, you probably think of something hard. All of the transitional metals, except for mercury (80), are in fact fairly hard. They are the workhorses of the periodic table—strong, stable metals used to make everything from airplanes to skyscrapers.

Notice the two empty spaces in the lower-left corner of this group? Those spaces are reserved for the lanthanide and actinide groups of elements, which we will talk about in a minute.

THIS NEXT BLOCK of elements represents three different groups.

The elements in the lower-left red triangle are known as the ordinary metals. The group of rust-colored elements in the upper-right triangle is known as the nonmetals. The orange group of elements in between is known as the metalloids, because these elements are kind of like metals and kind of not like metals.

THE SECOND-TO-LAST COLUMN of elements in the periodic table is called the halogens. This is a particularly nasty group, known for being violent and smelly when they’re out in the world on their own. But when they mix with elements from other groups, they can transform into pretty tame things—toothpaste and table salt, for example.

The elements that make up the last column are known as the noble gases. Sounds fancy, eh? The name comes from the fact that, like kings and other royalty, they don’t mix with the commoners from the rest of the table. Except for occasionally hanging out with fluorine (9), they form no chemical compounds.

THESE TWO GROUPS of elements sit just below the main periodic table and are known collectively as the rare earths. The top row is the lanthanides and the bottom row is the actinides. (These are the elements that fill up those two spaces left in the block of the transitional metals.)

Sometimes you will see the periodic table arranged with the rare earths slotted into those blank spaces, but then the table becomes very wide. So usually you see the rare earths arranged as two separate rows at the bottom.

NOW YOU’VE SEEN the periodic table as a whole, and you know how it’s arranged. In the rest of this book you will get to meet each of the 118 elements as individuals.

Glossary

ALLOY: A mixture of different metal elements.

ANODIZE: To send an electric current through the surface of a metal to form a hard, protective oxide coating.

ATOM: A tiny particle of matter made up of a nucleus (containing protons and neutrons) with electrons in orbit around it. Each atom is an atom of a particular element, determined by the number of protons in its nucleus. For example, an atom with six protons is a carbon atom; this is called the atomic number of the element.

COMPOUND: A substance containing two or more different chemical elements that are chemically bonded to each other in specific ratios (unlike an alloy, where there is no fixed proportion in the number of atoms of each type).

ELECTRON: A tiny, subatomic (smaller than an atom) particle with a negative electric charge. Electrons are responsible for creating the chemical bonds between atoms that form compounds.

EMISSION LINE: Light of a specific wavelength (color) emitted by an atom or compound when it is heated in a flame or electric arc.

HALF-LIFE: The length of time before half the atoms in a sample of a radioactive element will undergo radioactive decay (meaning energy from the nuclei gets released).

INERT: Resistant to involvement in chemical reactions.

ISOTOPE: Different isotopes of the same element are atoms of that element that have the same number of protons in their nucleus, but different numbers of neutrons.

NEUTRON: A subatomic (smaller than an atom) particle with zero electric charge and found in the nucleus of most elements.

ORE: A raw material, dug from the ground, that can be transformed into a metal by chemical or electrical means. Most ores are oxides: for example, iron ore is iron oxide, and aluminum ore is aluminum oxide.

OXIDE: A compound of oxygen and another element.

PIGMENT: A chemical compound with a particularly intense color that can be used in paints or inks.

PROTON: A subatomic (smaller than an atom) particle with a positive electric charge. The number of protons in the nucleus of an atom determines what element that atom is. This is called the atomic number of the element.

REACTIVITY: How easily an element or compound will engage in chemical reactions. Highly reactive chemicals can be dangerous, because they tend to react rapidly and release a lot of energy when they encounter other chemicals, including things like your skin or lungs.

SPECTRAL LINE: See Emission Line.

SUPERCONDUCTOR: A material that allows electricity to flow through it without any resistance.