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[edit] Structure

Protons, Neutrons and Electrons make up atoms. Because of this, they are called subatomic particles. Each type of atom can differ in the number of protons, neutrons, and electrons. According to the current electron-cloud theory of atoms, there are 2 parts to the atom, the nucleus and the electron cloud. The nucleus is made up of protons & neutrons, and in turn each of these nucleons is made up of triples of even smaller particles called "quarks".

The nucleus is the center of the atom and contains the protons and neutrons. The nucleus is very small compared to the size of the electron cloud. This means there is empty space around the nucleus. The protons and neutrons of an atom are in specific locations.

The protons have a positive charge. The number of protons decides what element an atom becomes. For example, if an atom has one proton, that means it is a Hydrogen element; only Hydrogen can have one proton. On the periodic table, the atomic number of the element is the same as its number of protons.

The neutrons have no charge, but they help to stabilize the nucleus; if the positive charges of the protons were by themselves in the nucleus, they would repel each other and make the nucleus less stable. Elements with differing numbers of neutrons but the same number of protons are called isotopes of each other. For example, Hydrogen has three isotopes, one with one neutron, one with two neutrons, and one with three neutrons. They all have one proton and so they are all Hydrogen, but because they differ in the number of neutrons they are different isotopes. Some isotopes are radioactive, which means that they decay, or lose their extra neutrons over time. A certain radioactive isotope of Carbon, called Carbon-14 is used by paleontologists to discover the age of fossils. They can do this because they know the rate at which Carbon-14 decays.

The outer part of the atom, or the electron cloud surrounds the nucleus. Now, according to a theory called Quantum Mechanics, we never know the exact location or speed of a specific electron; we can only say the probability of it being anywhere. If we know exactly where the electron is, than we don't know how fast it is going. If we know how fast it is going, likewise, we cannot determine where exactly it is located. The electrons have a negative charge. Some scientists used to think that electrons orbited the nucleus like planets around the sun, but we now know this isn't true. The electrons move randomly around the nucleus and are attracted to the positive charge of the protons in the nucleus. They let the atoms bond together to make molecules.

[edit] Atoms = Building Blocks

Atoms are the basis of chemistry. They are the basis for everything in the Universe. You should start by remembering that matter is composed of atoms. Atoms and the study of atoms are a world unto themselves. We're going to cover basics like atomic structure and bonding between atoms. As you learn more, you can move to the biochemistry tutorials and see how atoms form compounds that help the biological world survive.

[edit] Electron Arrangement

What keeps all the electrons in place? The answer is energy levels. These energy levels have little compartments inside which the electrons are kept. These are called orbitals. Each orbital can hold two electrons.

• In the first energy level, there is a maximum of one orbital, so two electrons can be kept in the first energy level.
• In the second energy level, there is a maximum of four orbitals, so eight electrons can be kept in the second energy level.
• Eighteen electrons are found in the third energy level.
• The fourth energy level contains up to thirty-two electrons.
• Less is known about the fifth level and so on.

As explained before, some atoms only have a certain amount of electrons, so some elements don't have as many orbitals or energy levels as others.