Physics world. Atoms. Isotopic Tracers

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Atom

Energy and matter are the two basic ideas in physics  Any­thing that makes up space and has weight is matter. It can be solid, liquid, or gas.

For example, ice is solid, water is liquid, and vapor is gas. Matter must have both volume and weight. Light and heat do not have weight, so they are not matter; they are energy. Matter is everywhere around us. Scientists study matter and divide it into smaller and smaller parts.

The smaller parts that scientists divide matter into are called molecules. A molecule is the smallest part of something that is itself divided into smaller parts. For example, a molecule of water (H₂O) is two parts hydrogen and one part oxygen. A molecule is the smallest part of water. Hydrogen and oxygen alone are not water.

Scientists divide molecules into smaller parts. These smaller parts are atoms. In ancient Greek philosophy the word atomwas used to describe the smallest bit of matter that could be con­ceived. This "fundamental particle," to use the present-day term for this concept, was thought of as indestructible; in fact, the Greek word for atom means "not divisible." Knowledge about the size and nature of the atom grew slowly throughout the centuries when people were content merely to speculate about it.

A sugar molecule contains three different kinds of atoms. One molecule of sugar has twelve carbon (C) atoms, twenty-two hydrogen (H) atoms, and eleven oxygen (O) atoms. Atoms are small pieces of matter. At present, scientists know about 100 different kinds of atoms in the world.

These 100 atoms combine in different ways to make all matter in the world.

The ten most common kinds of atoms in the world are oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg). These are elements. At­oms of different elements combine to make compounds. A com­pound consists of different elements.

Atoms are very tiny. Scientists can see themwith an electron microscope, and they study atoms in other ways too. An atom has

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two main parts: the nucleus and electrons. The nucleus is the center of the atom. Electrons are tiny parts that go around the nu­cleus. The nucleus also has two parts: protons and neutrons. There is the same number of protons in the nucleus as there are electrons in the atom. Electrons, protons, and neutrons, then, are the three parts of an atom.

Parts of the atom have electrical charges. Protons have a posi­tive (+) electrical charge; neutrons have no electrical charge; and electrons have a negative (-) charge. In an atom, there is the same number of protons and electrons. Therefore, the positive protons balance the negative electrons, and an atom is electrically neutral.

 All atoms contain protons, neutrons and electrons. Different atoms have different numbers of these particles. For example, aluminum has thirteen electrons, thirteen protons and fourteen neutrons. Iron has twenty-six protons, twenty-six electrons and thirty neutrons.

Scientists divide matter into its smallest parts. Atoms are small parts of matter. They are made up of electrons, protons, and neu­trons. Scientists study atoms to learn more about matter.