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Added info on subatomic particles, ions.
An atom is the smallest unit of chemical element that still retains the element's properties. The word atom comes from the Greek term for indivisible, ''átomos''. There have been many ideas about how atoms may look. The current one is called the [[Quantum Mechanical Model]]{{fact}}, and is very complex.{{fact}}
An '''atom''' is the smallest unit of chemical element that still retains the element's properties. The word atom comes from the Greek term for indivisible, ''átomos''. There have been many ideas about how atoms may look. The current one is called the [[Quantum Mechanical Model]]{{fact}}, and is very complex.{{fact}}
==Structure==
Atoms are comprised of three subatomic particles: positively charged [[proton|protons]], electrically neutral [[neutron|neutrons]] and negatively charged [[electron|electrons]]. Protons and neutrons are contained in close proximity in the centre of an atom, forming the [[nucleus]]. Electrons inhabit the space around the nucleus, and are arranged around it in a series of layers, known as [[electron shell|shells]] or energy levels.
===Atomic Number===
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===
Atoms are normaill electrically neutral; thry have no charge. However, elctrtons in the [[valence shell]] can be gained or lost (depending on the element and the conditions) to form an [[Ion|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.
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<sup>+</sup>) and [[chlorine]] anions (Cl<sup>-</sup>) in equal proportions. The negatively charged chlorine 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.
[[Category:Chemistry]]
[[Category:Chemistry]]
[[Category:Physics]]
[[Category:Physics]]