Chemistry

Atoms and Molecules


1. A Positively Charged Ion is Known as Cation


Sodium ion, Na+,and magnesium ion, Mg2+, are cations because they are positively charged ions.A cation is formed by the loss of one or more electrons by an atom.For example, sodium atom loses 1 electron to form a sodium ion, Na+, which is a cation :
Since a cation is formed by the removal of electrons from an atom, therefore,a cation contains less electrons than a normal atom. We also know that a normal atom (or a neutral atom) contains an equal number of protons and electrons. Now, since a cation is formed by the loss of one or more electrons by an atom, therefore,a cation contains less electrons than protons. The ions of all the metal elements are cations. Only the hydrogen ion, H+,and ammonium ion, NH+4,are the cations formed from non-metals. We will now give the reason for the positive charge on a cation.
We know that a proton has 1 unit positive charge and an electron has 1 unit negative charge. Now,a normal atom contains an equal number of protons and electrons, so it is electrically neutral. When a normal atom loses electrons to form a cation, then in this cation, the number of electrons becomes less than the number of protons. In other words, we can say that a cation has more protons than electrons.Due to more protons than electrons, a cation has a positive charge on it.This will become more clear from the following example.
Let us write down the number of protons and electrons in a sodium atom as well as a sodium ion as shown below :
Sodium atom,Na,contains 11 protons and 11 electrons. Since the number of protons and electrons in a sodium atom is equal, it is electrically neutral, having no overall charge. In the sodium ion, Na+, there are 11 protons but only 10 electrons. This means that there is 1 proton more than electrons. Due to 1 more proton (than electrons), a sodium ion has 1 unit positive charge and it is written as Na+
All the metal atoms can lose electrons easily, so all the metal elements form cations (or positive ions).Please note that:
(i) If an atom loses 1 electron, then the cation (positive ion) formed has 1 unit positive charge. For example, a sodium atom loses 1 electron to form a sodium ion, Na+, having 1 unit positive charge.
(ii) If an atom loses 2 electrons, then the cation (positive ion) formed has 2 units of positive charge.For example, a magnesium atom can lose 2 electrons to form a magnesium ion,Mg2++,having 2 units of positive charge.
(iii) And if an atom loses 3 electrons, then the cation (positive ion) formed has 3 units of positive charge. For example,an aluminium atom can lose 3 electrons to form an aluminium ion, Al3+, having 3 units of positive charge.
It is, however, usually not possible to remove more than 3 electrons from an atom due to very high energy required for this purpose. Another point to be noted is that the electrons lost by a metal atom during the formation of a cation (positive ion) are accepted by a non-metal atom (which then turns into an anion or negative ion).

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Notes


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