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H 1.31 N : a) b) urea an isomer of urea 1.32 Period 2 elements can accommodate only 8 valence electrons; hence the octet rule. Atoms in periods beyond 2 can hold more than 8 electrons in their valence shell. Phosphorus is a period 3 element can accommodate more than 8 electrons in its valence shell, which allows it to form more than 3 bonds. Nitrogen (a period 2 element) has a capacity for only 8 electrons in its outer shell, limiting it to 3 bonds and an unshared pair of electrons, or 4 bonds and a positive charge. Cl : Cl P Cl Cl Cl Cl 1.33 The absence of the two unpaired electrons in the +2 unstable species NH₃ results in a formal charge H-N-H of +2 on the nitrogen. H 1.34 F: +1 O O -1 0 0 -1 Ozone is bent at the central O. The actual structure of ozone is a hybrid of the two resonance structures shown, so the bonds are identical. 1.35 -1 -1 0 C -1 C : C : 0 O: -1:0 -1 : The carbonate anion has trigonal planar geometry at its carbon. All the oxygens are identical because there are three resonance structures. 9