CHEMISTRY

Other pages in the Chemistry area

Introduction		Ionic Compounds
Atomic Theory		Ions
Covalent Compounds		Periodic Table
Chemical Formulae		Polyatomic Ions

Atomic Theory

Everything that occupies space is called matter. In general, matter is a complex mixture of various types. To make sense of the structure of matter, search for those bits of matter which seem to be the simplest. There are a number of substances that can not be broken down physically or chemically into simpler forms. These are called elements.

Elements
An element can be defined as matter that cannot be separated into any simpler substances by a physical or a chemical process. Over 100 elements have been identified and scientists believe that all the matter in the universe is made up from these 100 or so elements, combined in millions of different ways. Many elements occur naturally on Earth (about 92), while others can be produced under artificial conditions.

Atoms
Within the atomic theory, each element is an aggregation of millions of identical particles called atoms. The atom is the smallest particle of an element that still retains the unique characteristics of that element. Atoms are very tiny and are invisible, even under the most powerful microscope. So, how do we know there are such things as atoms when we can't see them? Within the atomic theory, predictions can be made regarding expected behaviour of particles such as atoms. So far the evidence supports the idea that matter is made up of atoms.

Protons, electrons and neutrons
The atomic theory suggests that atoms are made up of even tinier particles called protons and neutrons (in the nucleus of the atom), and still tinier particles called electrons (surrounding the nucleus). Protons have a positive charge, electrons have a negative charge, while neutrons have no electrical charge. Again, it is the predictive behaviour of atoms that provide evidence to support these ideas.

An atom is electrically neutral because it has the same number of protons and electrons. The positive and negative charges cancel each other out. Electrons, however, can move to or from atoms, resulting in a “charged atom” called an ion.

Naming and describing elements
Each element has a different name and symbol. Chemical symbols are 1 or 2 letters, the first letter always written as a capital while the second letter (if present) is lower case. For example H is the symbol for hydrogen, He is the symbol for helium, Li is the symbol for lithium, and so on ....there are some easy ways to remember these.

So, if all elements are made up of atoms consisting of the three basic particles (protons, neutrons and electrons), why does each element look or behave differently to each other? Elements differ from each other simply because their atoms have different numbers of protons (and therefore electrons). Somehow, the number of protons is very important to the way the element behaves. For instance, at room temperature carbon (six protons) is a solid, important in the basic structure of living organisms, nitrogen (seven protons) is a clear gas making up 78% of the air, oxygen (eight protons) is a clear, combustible gas vital for human life, fluorine (nine protons) is a poisonous, highly reactive gas, neon (ten protons) is an non-reactive gas, while sodium (11 protons) is a very reactive metallic solid. An extra proton (and, therefore, electron) here or there makes a big difference.

Atomic number
The atomic number of an element is the number of protons associated with an atom of that element. The appearance, reactivity and other characteristics of elements can be shown to follow a pattern that is closely related to the atomic number. The patterns have been summarised within the periodic table of elements.

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