## Chapter 4

## Q. 4.6

Assign an oxidation number (oxid. no.) to each element in the following species:

(a) N_{2} (b) N^{3-} (c) NO_{3}^{-} (d) BaO (e) K_{2}O_{2}

## Step-by-Step

## Verified Solution

oxid. no. N = 0 | (a) N_{2} is in its elementary state. (Rule 1) |

oxid. no. N = -3 | (b) N^{3-} is a monoatomic ion. (Rule 2) |

oxid. no. O = -2
3(-2) + x = -1; oxid. no. N = +5 |
(c) There are no Group 1 or Group 2 metals. (Rule 6)
NO_{3}^{-} is a polyatomic ion. (Rule 5) |

oxid. no. Ba = +2
+2 + x = 0; oxid. no. O = -2 |
(d) Ba is a Group 2 metal. (Rule 3)
The sum of the oxidation numbers is 0. (Rule 5) |

oxid. no. K = +1
2(1) + 2x = 0; oxid. no. O = -1 |
(e) K is a Group 1 metal. (Rule 3)
The sum of the oxidation numbers is 0. (Rule 5) |

**END POINT**

Always look for the “leading elements” (Group 1 and Group 2 metals and F) in a compound when you start. These elements will lead you to the oxidation numbers of the other elements in the compound. If these leading elements are not present, then look for H and O (+1 and -2, respectively, when not combined with Group 1 or 2 metals.)