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Basic Chemistry Concepts

Chemical Elements

common English names, letter symbols, Latin names, oxygen atom, atomic weight

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>  Origin of Elements

>  Abudance of Elements

>  Classification of Elements

Chemical Elements, substance made up only of atoms that all have the same atomic number. The atomic number is the number of protons in the atom’s nucleus: element atomic number 1 hydrogen has one proton in the nucleus and the element atomic number 92 uranium has 92 protons. Ninety-four natural elements have been detected in the universe. More than 110 elements have been identified, with some created only in laboratories as artificial elements. Under certain conditions, one element may be changed into another element through processes that add or remove protons from a nucleus.

Although the number of protons in the nucleus of a particular chemical element is always the same, the number of neutrons can vary, creating isotopes of that element that have different atomic masses and physical properties. The chemical properties of an element are mainly determined by the number of electrons in the outermost shell of an atom of that element. The number of electrons is the same as the number of protons in the nucleus of an element. The unit for atomic weight of the elements is one-twelfth of the weight of the carbon-12 atom, which is arbitrarily set at 12.

Atoms of a single element may combine to form molecules of that element—two atoms of oxygen combine to form oxygen molecules, eight atoms of sulfur combine to form sulfur molecules. Atoms of different elements may combine to form molecules of chemical compounds—two hydrogen atoms combine with one oxygen atom to form molecules of water. Unlike chemical compounds, elements cannot be broken down into simpler substances by ordinary heat, light, electricity, or chemical reactions. Like other forms of matter, most elements can exist as gases, liquids, or solids, depending on the pressure and temperature.

Scientists use one- and two-letter symbols for each element. In some cases these symbols are based on old Greek or Latin names for the elements and don’t correspond to their common English names. For example, hydrogen is H, but gold is Au, from Latin aurum.



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