Chemistry

Atoms and Molecules


Formula Unit of Ionic Compounds


Before we describe formula mass, we should know the meaning of 'formula unit' of an ionic compound.This is discussed below. An ionic compound is made up of an extremely large number of positively charged ions and negatively charged ions joined together. For example, sodium chloride is an ionic compound which consists of a large (but equal) number of sodium ions, Na+,and chloride ions,Cl-, so the actual formula of sodium chloride compound should be (Na+)n (Cl-)n or (Na+Cl-)n, where tt is a very large number (see Figure 42). NaCl is the simplest formula of sodium chloride and not its actual formula.
The simplest combination of ions that produces an electrically neutral unit, is called a 'formula unit'of the ionic compound. The 'formula unit' of an ionic compound can be thought of as the smallest unit of that compound, it is the equivalent of a 'molecule'of the compound.The formula unit of sodium chloride compound is NaCl (which consists of one Na+ ion and one Cl- ion) (see Figure 43). The formula unit of ammonium sulphate is (NH4)2SO4 It consists of two NH4+ ions and one SO42- ion.

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Notes
Atoms and Molecules - Notes
1. Drawbacks of Dalton’s Atomic Theory
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2. Monovalent Cations (Cations Having a Valency of 1+)
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3. Divalent Cations (Cations Having a Valency of 2+)
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4. Dalton’s Symbols of Elements
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5. Trivalent Cations (Cations Having a Valency of 3+)
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6. Formulae of Some Molecular Compounds
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7. An Important Discussion
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8. an example, let us give the significance of symbol C
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9. Molecular Formulae of Some Common Elements
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10. Chemical Formulae
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11. 2. A Negatively Charged Ion is Known as Anion
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12. As an example, let us give the significance of the formula H2O
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13. Molecules
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14. Molecules of Compounds
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15. Molecular Mass
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16. Explanation of the Law of Conservation of Mass
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17. Some Ionic Compounds
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18. Atoms, Molecules and Ions
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19. Atoms
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20. Formula Mass
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21. Formulae of Elements
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22. Mole of Molecules
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23. Simple Ions and Compound Ions (Polyatomic Ions)
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24. 1. A Positively Charged Ion is Known as Cation
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25. Symbols of Elements
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26. 1. Molecules of Elements
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27. Formulae of Compounds
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28. Gram Atomic Mass And Gram Molecular Mass
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29. Mole of Atoms
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30. John Dalton
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31. Ions
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32. Explanation of the Law of Constant Proportions
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33. Dalton's Atomic Theory
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34. Significance of the Formula of a Substance
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35. Some Common Ions
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36. Molecular Masses of Some Common Elements
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37. Laws Of Chemical Combination
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38. Ionic Compounds
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39. Calculation of Molecular Mass
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40. Divalent Anions (Anions Having a Valency of 2-)
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41. Formula Unit of Ionic Compounds
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42. Atoms And Molecules
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43. How Do Atoms Exist
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44. Writing Of Formulae Of Ionic Compounds
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45. Problems Based On Moles Of Molecules
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46. Gram Molecular Mass
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47. Experiment to Verify Law of Conservation of Mass
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48. Gram Atomic Mass
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49. Laws Of Conservation of Mass
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50. Writing Of Formulae Of Molecular Compounds
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