Thursday

Raven unrolls a chart across the Bench. Rows and columns of little boxes cover it, each with a number, a symbol and a name.

"The periodic table," she says. "Every kind of atom in the universe, on one page."

Rocket counts along the top row. "One, two. Then this row has eight. Why is it shaped like a castle?"

"What do you notice about the numbers?" Raven asks. Rocket runs his finger across. "They go up by one. Hydrogen is 1. Helium is 2."

Nova floats over the chart and lights up one box, then another. "Those numbers count something inside each atom," she says. "Something every element has a different amount of."

"Protons," Rocket whispers. Raven grins and opens the Bench Log to a fresh page.

Atoms are the building blocks of matter. They are the smallest particles of an element that still have the element's properties.

An element is a pure substance made of only one type of atom. It cannot be broken down into a different substance.

There are 118 known elements. Ninety eight occur naturally on Earth, and 20 have been made in laboratories.

All matter in the universe is built from these 118 kinds of atoms. Millions of words are built from one small alphabet in the same way.

The periodic table displays all the known elements in order of increasing atomic number.

The National Institute of Standards and Technology publishes a periodic table as a wall chart. Each box gives the atomic number, the symbol and the name.

The atomic number of an element is the number of protons in the nucleus of each of its atoms.

Hydrogen, at the upper left, has atomic number 1. Every hydrogen atom has one proton. Helium atoms have two protons, lithium atoms have three, and so on.

A horizontal row is called a period. There are seven periods. Period 1 has only two elements, hydrogen and helium, while periods 2 and 3 have eight each.

A vertical column is called a group. There are 18 groups, numbered 1 to 18 from left to right. Elements in a group have similar properties.

The last element, number 118, is oganesson. It completes the seventh period.

Here are ten elements from the table, with data from the National Institutes of Health PubChem periodic table.

Some symbols do not match their English names. Fe for iron and Au for gold come from the elements' Latin names.

An oxygen atom has 8 protons, 8 neutrons and 8 electrons. A hydrogen atom has 1 proton and 1 electron.

In every atom, the number of electrons equals the number of protons, so atoms are neutral in charge.

Strong reading. Tomorrow you will find these elements in the air, in the kitchen and in the wires in your walls.