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