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[[Image:Atoms1.jpg|thumb|right|Subatomic resolution of atoms by AFM]]

[[Image:Atoms1.jpg|thumb|right|Subatomic resolution of atoms by AFM]]

An '''atom''' is

An '''atom''' is

a [[particle]] of [[matter]] indivisible by [[chemical]] means <ref>[http://www.lbl.gov/abc/Glossary.html Glossary of Nuclear Terms] </ref> which form the building blocks of molecules.

a [[particle]] of [[matter]] indivisible by [[chemical]] means <ref>[http://www.lbl.gov/abc/Glossary.html Glossary of Nuclear Terms]</ref> which form the building blocks of molecules.

Although the word "atom" comes from the Greek term for indivisible, ''átomos'', atoms are actually made up of three different kinds of subatomic particles; some of these are composed of yet smaller particles.

Although the word "atom" comes from the Greek term for indivisible, ''átomos'', atoms are actually made up of three different kinds of subatomic particles; some of these are composed of yet smaller particles.

Those who understand electrical theory might notice that positively charged particles packed closely together would repel one another. The nucleus stays together because of what is known as the ''strong nuclear force''. The quantization of this force is a tiny particle called a "gluon".  

Those who understand electrical theory might notice that positively charged particles packed closely together would repel one another. The nucleus stays together because of what is known as the ''strong nuclear force''. The quantization of this force is a tiny particle called a "gluon".  

===Atomic Number===

==Atomic Number==

[[Image:Isotopes.jpg|right|thumb|Isotopes]]

[[Image:Isotopes.jpg|right|thumb|Isotopes]]

Chemical elements are made up of atoms with certain properties. The number of protons in the nucleus of an atom (known as the [[atomic number]]) determine the properties of the atom, and the element it constitutes. For example, [[Hydrogen]] has one proton, and therefore an atomic number of 1. [[Oxygen]] has 8 protons in its nucleus and has an atomic number of 8. Under normal conditions, atoms contain an equal number of protons and electrons.

Chemical elements are made up of atoms with certain properties. The number of protons in the nucleus of an atom (known as the [[atomic number]]) determine the properties of the atom, and the element it constitutes. For example, [[Hydrogen]] has one proton, and therefore an atomic number of 1. [[Oxygen]] has 8 protons in its nucleus and has an atomic number of 8. Under normal conditions, atoms contain an equal number of protons and electrons.

===Ions===

==Ions==

Atoms are normally electrically neutral; they have no charge. However, electrons in the [[valence shell]] can be gained or lost (depending on the element and the conditions) to form an [[ion]]. An atom that loses electrons becomes positively charged and is known as a cation. An atom that gains electrons electrons becomes negatively charged and is known as an anion. Anions of the common elements fluorine, chlorine, bromine and iodine are known as fluoride, chloride, bromide and iodide (replacing -ine with -ide), respectively.

Atoms are normally electrically neutral; they have no charge. However, electrons in the [[valence shell]] can be gained or lost (depending on the element and the conditions) to form an [[ion]]. An atom that loses electrons becomes positively charged and is known as a cation. An atom that gains electrons electrons becomes negatively charged and is known as an anion. Anions of the common elements fluorine, chlorine, bromine and iodine are known as fluoride, chloride, bromide and iodide (replacing -ine with -ide), respectively.

Many common substances are made up of ions. For example, [[sodium chloride]] (NaCl), otherwise known as table salt, is made up of [[sodium cations]] (Na⁺) and [[chlorine]] anions (chloride, Cl^-) in equal proportions. The negatively charged chloride ions are attracted to the positively charged sodium ions, forming an [[ionic bond]]. This results in a lattice structure, which is responsible for sodium chloride being crystalline in its solid state.

Many common substances are made up of ions. For example, [[sodium chloride]] (NaCl), otherwise known as table salt, is made up of [[sodium cations]] (Na⁺) and [[chlorine]] anions (chloride, Cl^-) in equal proportions. The negatively charged chloride ions are attracted to the positively charged sodium ions, forming an [[ionic bond]]. This results in a lattice structure, which is responsible for sodium chloride being crystalline in its solid state.

===Isotopes===

==Isotopes==

Atoms of the same element that have different numbers of neutrons are known as [[isotope|isotopes]]. Some isotopes are more stable than others, and occur more often in nature, but there is no "standard" number of neutrons in a given element. The atomic weight of an element is a weighted average of the number of neutrons and protons (number of protons remains constant in a given element) in all naturally occurring isotopes. Many isotopes are [[radioactive]] and [[decay]] over time.

Atoms of the same element that have different numbers of neutrons are known as [[isotope]]s. Some isotopes are more stable than others, and occur more often in nature, but there is no "standard" number of neutrons in a given element. The atomic weight of an element is a weighted average of the number of neutrons and protons (number of protons remains constant in a given element) in all naturally occurring isotopes. Many isotopes are [[radioactive]] and [[decay]] over time.

==See also==

==See also==