please say me the how to write chemical compound
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Number of atoms or molecules
The number preceding an element symbol or compound formula tells how many atoms or molecules. If no number appears before the symbol, there is only one atom or molecule. For example, consider the formula for the chemical reaction that forms carbon dioxide, C + 2O → CO2. The number 2 preceding the oxygen symbol O shows that there are two oxygen atoms in the reaction. The lack of a number preceding the carbon symbol C and the compound formula CO2 shows that there is one carbon atom and one carbon dioxide molecule.
Meaning of Subscript Numbers
Subscript numbers in chemical formulas represent the number of atoms or molecules immediately preceding the subscript. If no subscript follows the chemical symbol, only one of the element or compound occurs in the molecule. In the example of carbon dioxide, CO2, the subscript 2 following the oxygen symbol O says that there are two oxygen atoms in the compound CO2, and no subscript following the symbol C says only one carbon atom occurs in the molecule. More complex molecules like the nitrate ion NO3 will be enclosed in parentheses if more than one occurs in the formula and the subscript will be placed outside the closing parenthesis. For example, the compound magnesium nitrate is written as Mg(NO3)2. In this example, the compound has one magnesium atom and two nitrate molecules.
Meaning of Superscript Numbers and Signs
Superscript numbers and signs represent the charges of ions. Ions can be individual atoms or polyatomic. Most polyatomic ions have negative charges. Negative charges happen when the number of electrons is greater than the number of protons. Positive charges occur when the number of protons exceed the number of electrons.
In the example of magnesium nitrate, the chemical reaction formula is:
Mg2+ + 2(NO3)- → Mg(NO3)2
The superscript 2+ (which can also be written as +2 or ++) shows that the magnesium ion has two extra positive charges while the superscript - shows that the nitrate ion NO3 has one negative charge. Since the final molecule has to be neutral, the positives and negatives must cancel each other out to add to zero. So, one positive magnesium ion with its 2+ charge combines with two negative nitrate ions, with one negative charge each, to form the neutral magnesium nitrate molecule:
2 + 2(-1) = 2 - 2 = 0
Numbers and Chemical Prefixes
Many formulas use Latin and Greek prefixes to identify the number of atoms or ions in the compound. Common prefixes include mono (one or single), bi or di (two or double), tri (three), tetra (four), penta (five), hexa (six) and hepta (seven). For example, carbon monoxide has one carbon atom and one oxygen atom while carbon dioxide has one carbon atom and two oxygen atoms. The chemical formulas are CO and CO2, respectively