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Glossary

Atomic Number	Atom	Electron	Element
Gravity	Mass	Matter	Neutron
Nucleus	Property	Proton	State

 

Atomic Number

The atomic number is the number of protons that are in the nuclei (centers) of the atoms of a chemical element. For example, oxygen has an atomic number of 8 because all oxygen atoms have eight protons in their nuclei. (Nuclei is the plural of nucleus)

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Atom

An atom is the smallest part into which an element can be broken down. An atom is a small particle (piece) of matter. It is made up of even smaller particles called protons, which carry a positive (+) electrical charge; neutrons, which have no charge; and electrons, which have a negative (-) charge.

 

All matter is made up of these tiny atoms; they are the building blocks of everything on Earth. Atoms are so small that a head of a straight pin has about 60 billion of them. The ancient Greeks were the first to guess that matter might be made up of small particles. Atoms contain even smaller particles called protons, neutrons, and electrons.

 

An atom is about one ten thousand millionth of a meter across. However, most of the mass of an atom lies in a tiny cluster at its center, called the nucleus. The nucleus is so small that if it were the size of a plum, then the whole atom would be as big as an Egyptian pyramid.

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Electron

An electron is a negatively charged particle. Electrons move around the nucleus (center) of an atom within regions called orbitals. There is a maximum number of electrons that each orbital can hold.

The electrons have very little mass. Each electron stays within its own orbital - a particular region of space around the nucleus. The amount of energy an electron has depends on which orbital it is in.

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Element

An element is a substance that cannot be broken down by chemical means. All the atoms in an element have the same chemical properties. Each element has a different atomic number. This is the number of protons (positively charged particles) in the nucleus of each of its atoms.

 

All the atoms in a particular element behave in the same way chemically, and they share the same atomic number. So far at least 109 elements have been discovered; 95 occur in nature, the others are made artificially (by scientists) in nuclear reactors or particle accelerators.

There are two main kinds of elements: metals and nonmetals. Most elements chemically combine with other elements to form substances called compounds.

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Gravity

Gravity is a force that operates between all objects in the Universe. It is mutually attractive which means both objects attract each other. The strength of the gravity is determined by the mass of the objects involved (greater mass causes greater attraction) and their distance apart. Gravity is the force that holds us on Earth and keeps the Earth and the planets orbiting the Sun. Everything on Earth is pulled down to the Earth's surface by gravity, and this pull gives objects their weight.

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Mass

Mass is the amount of matter an object contains.

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Matter

Matter is anything that occupies a space and has mass. Everything in the Universe is a form of matter, except forms of pure energy, such as light. All matter consists of a variety of tiny particles. The most common of these are protons, neutrons, and electrons, which are usually bound together in atoms.

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Neutron

A neutron is a particle that carries no electrical charge. Neutrons are contained in the nucleus (center) of an atom along with positively charged particles called protons. Neutrons and protons each have a mass unit of one.

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Nucleus

The nucleus is the central part of an atom. The nucleus contains nearly all of an atom's mass. The plural of nucleus is nuclei.

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Property

A property describes how a matter looks, feels, acts or behaves.

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Proton

A tiny particle that carries a positive electrical charge. Protons are contained in the nucleus (center) of an atom. The number of protons in an atom is the same as the number of electrons (negatively charged particles). The number of protons in an atom of an element gives the atomic number of that element.

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State

A state of matter is a group of matter that has the same properties.

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