What Are The Building Blocks of Matter?

The world is made up of all sorts of things.
Just look around you.
There are houses, cars, trees, and people.
All these things are different shapes, sizes, and colors.
Look closely at some of them.
They are made from different materials.
Some are hard and cold. Others are soft and warm. They may be wet or dry, rough or smooth.
All these things look and feel different to us.
The different things in the world have two things in common. They are all made of something, which means they have substance, and they all take up space.
Anything which takes up space is called matter. 
So a pencil, a book, a house, a tree, the air, and everything around you is matter. You are matter, too. The whole earth is matter, and so are the stars throughout the universe and the dust that drifts between them.
Imagine you are using a knife to divide a drop of water or a grain of sand. You can divide them again and again, until the pieces are so small that you can no longer see them. Scientists can divide these tiny particles of matter even smaller under a powerful microscope. They divide them again and again, until the particles are so small that they can no longer be seen clearly, even under the microscope. Whatever in the end makes up matter is so small that we cannot see it.
But everything in the world—animal, vegetable, mineral, solids, liquids, and gases—is made of matter.

Space and energy

Because space has no substance and obviously does not take up space, it does not qualify as matter. Neither does energy, which is the ability to do work.
However, matter and energy are not completely separate. Many scientists believe that matter and energy are two aspects of the same thing, like liquid water and ice are two aspects of water.

The building blocks of matter

Have you ever played with building blocks?
The blocks can be joined together to make all kinds of things.
Scientists think this is how the world is made up. Tiny particles join together, like building blocks, to make up matter. 
The matter in the universe is made from tiny particles called atoms. Millions and millions of atoms combine to make the different things around us—even the air we breathe.
Atoms are the building blocks of matter.
Atoms are so small that they can't be seen. But scientists can take photographs of atoms using electron microscopes. With the help of these photographs, scientists can describe what atoms are like and build models to show how they behave.

Imagine that an atom is like a tiny solar system. In the center of the atom, there is a part called the nucleus.
The nucleus contains particles called protons and neutrons.
Whirling around the nucleus are much smaller, lighter particles called electrons, always in motion. You can think of the nucleus as the sun, and the electrons as the earth and other planets circling around the sun. 
There is constant motion in matter.
Matter around us is made up of atoms.
But there is more than one type of atom. In fact, there are over one hundred different types, which make up the elements.
Elements are substances which are made up of many of the same type of atom. The metal called iron is an element made up of iron atoms.
The gas called hydrogen is an element normally made up of pairs of hydrogen atoms.
Elements are the simplest chemical substances.
We don't often deal with atoms. Rather, we deal with the elements.
How can we tell an atom of iron from an atom of hydrogen? 
Each atom is made up of electrons circling around a nucleus. The nucleus is made up of protons and neutrons. An atom of hydrogen has only one proton and one electron. An atom of iron has 26 protons and 26 electrons. The number of neutrons can vary. But hydrogen will always have one proton and one electron, and iron will have 26 protons and 26 electrons. The number of protons determines the element.