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Ions And Their Compound

Published in: Physics
  • Mayank K

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A brief descriptions about ions

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    Ions ' An ion is a charged species in which an atom or a group of atoms possess a net electric charge. The net electric charge of an ion can either be positive or negative. Positively charged ions are called cations and negatively charged ions are called anions.
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    ' Molecules that are composed of metals and non-metals contain charged species. For example, potassium chloride (KCI) consists of K+ ion (cation) and CI— ion (anion). Similar to molecules, an ion can be monoatomic, diatomic, tetra-atomic, etc. Ions may consist of a single charged atom or a group of atoms that have a net charge over them. A group of atoms carrying a charge are known as polyatomic ions.
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    The name of some common ions with their symbols is given below Cation Aluminium Calcium Cuprous ion Cupric ion Hydrogen Ferric ion Nickel Silver Symbol A13+ Ca2+ Cu+ Cu2+ Fe3+ Ni2+ Ag+ Atomicity Monoatomic Monoatomic Monoatomic Monoatomic Monoatomic Monoatomic Monoatomic Monoatomic Anion Bromide Chloride Fluoride Hydride Hydroxide Iodide Nitride Oxide Symbol cl- F— OH- 1- Atomicity Monoatomic Monoatomic Monoatomic Monoatomic Diatomic Monoatomic Monoatomic Monoatomic
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    4.4 Ionic compounds ' Compounds in which molecules are formed by the combination of cations (positively charged ions) and anions (negatively charged ions) are known as ionic compounds. For example, zinc oxide (ZnO). This is formed by the combination of zinc ion (Zn2+) and oxide ion (02—). Other examples of ionic compounds are magnesium chloride (MgC12), potassium bromide (KBr), sodium chloride (NaCl), etc.
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    The table given below illustrates some examples of ionic compounds. Ionic Compound Calcium oxide Magnesium chloride Aluminium sulphide Combining Elements Calcium, oxygen Magnesium, chlorine Aluminium, sulphur Ratio by mass 24:71 27:32 Ratio by number of ions
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    50 Writing Chemical Formulae Of Compounds ' Chemical formula of a compound is the symbolic representation of its atomic constituents. In other words, a chemical formula represents the composition of a molecule in terms of the symbols of the elements present in that molecule. To write the chemical formula of a compound, one should have prior knowledge of two things: ' 1.The symbols of the constituent elements, and ' 2.The combining capacity of each atom constituting the compound
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    ' We know that the combining power or the combining capacity of an atom or an element is called its valency. The number of atoms of other elements with which one atom of an element combines is decided by the valency of that element. ' For example, both hydrogen and chlorine have a valency of 1. Therefore, one atom of hydrogen reacts with one atom of chlorine to form one molecule of hydrogen chloride. ' The valency of an ion is equal to the charge on it.
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    The valencies of some common ions are given in the following table. Name of ion Aluminium Ammonium Calcium Copper(ll) Hydrogen Iron(ll) Iron(lll) Potassium Zinc Symbol coi ca2+ cu2+ Fe2+ Fe3+ zn2+ Valency 3 1 2 2 1 2 3 1 2 Name of ion Sulphite Bromide Carbonate Chloride Hydride Hydrogen carbonate Hydroxide Oxide Sulphide Symbol soi co: HCO; OH 02 S2 Valency 2 1 2 1 1 1 2 2
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    ' While writing the chemical formula, certain rules need to be kept in mind. These rules are given below: ' The valencies or charges on the ions must be balanced. ' In case of a compound consisting of a metal and a non-metal, the symbol of the metal is written first. For example, in calcium chloride (CaC12) and zinc sulphide (ZnS), calcium and zinc are metals, so they are written first, whereas chlorine and sulphur are non-metals. ' (iii) In case of compounds consisting of polyatomic ions, the polyatomic ions are enclosed in a bracket before writing the number to indicate the ratio. For example, in aluminium sulphate [A12 (S04)3], the polyatomic sulphate ion is enclosed in a bracket before writing
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    ' Compounds composed of two different elements are called binary compounds. These are the simplest compounds. While writing the chemical formulae for compounds, we first write the constituent elements and their valencies and then crossover the valencies of the combining atoms.
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    For exarnple 0 0 00 0 00 ' Formula of calcium oxide ' Symbol Ca O ' Charge 2+2- ' Thus, the chemical formula of calcium oxide is CaO..
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    ' Formula of aluminium sulphate Al S04 ' Charge 3+2- aluminium sulphate is A12(S04)3. Brackets are ' Thus, the formu used when we have two or more of the same ions in a formula. Here, the bracket with a subscript 3 indicates that three sulphate groups are joined to two aluminium atoms.


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