Chemistry · Ch 5 — Chemical Bonding
Lewis structures (Lewis representations of simple molecules)
Lewis structures (Lewis representations of simple molecules)
A Lewis dot structure is a diagram that pictures a molecule's or ion's bonding purely in terms of shared electron pairs (bonds) and lone pairs, built around the octet rule. Such a diagram does not fully capture everything about a molecule — most notably, it says nothing directly about its three-dimensional SHAPE, and it cannot always predict a molecule's true magnetic or energetic behaviour — but it remains a simple and genuinely useful first picture of how a molecule's atoms are connected, how many bonds link them, and where any lone pairs sit. Lewis structures can be drawn for molecules built from identical atoms (H2, O2) as readily as for molecules built from different atoms (NF3, HNO3), and — as the worked nitrite-ion example in this section shows — for polyatomic IONS as well as neutral mo …
Table 5.2 lists Lewis structures for H2, O2, O3, NF3, CO3²⁻ and HNO3. NOTE ON SOURCE FIDELITY: the raw PDF-extracted text for this table is badly scrambled (dot/bracket/superscript characters and molecule labels are interleaved out of order — exactly the 2-D-layout garbling risk flagged for this chapter), so the individual dot-and-dash positions could not be reliably read back from the source. The structures below are therefore each given from standard, well-established chemistry rather than guessed from the garbled layout: H2 — H:H or H–H, one shared pair, no lone pairs. O2 — commonly drawn at this level as O=O, each O carrying two lone pairs (the simple Lewis picture; it does not capture O2's true paramagnetism, which needs MO theory, section 5.5). O3 (ozone) — a bent, resonance-stabilised structure, one terminal O double-bonded and the other single-bonded to the central O, central O bearing a formal +1 charge and the singly-bonded terminal O bearing formal −1 (see the worked formal-charge example under section 5.2.6). NF3 — N is the central, least-electronegative atom, singly bonded to three F atoms, each F carrying three lone pairs, and N carrying one lone pair (pyramidal arrangement). CO3²⁻ — C is central with one C=O double bond and two C–O single bonds (each singly-bonded O carrying a −1 formal charge, C formally neutral, the two negative charges given by the ion's 2− overall charge), stabilised by resonance among three equivalent canonical forms. HNO3 (nitric acid) — H is bonded to one O, that O …
Worked out. Worked example from the book. Step I: count total valence electrons — N contributes 5, each of the two O atoms contributes 6, plus 1 extra electron for the ion's negative charge: electrons. Step II: the skeletal structure is O–N–O. Step III: draw one single bond (one shared pair) from N to each O, which completes the octet on both O atoms but leaves N's octet incomplete; so one N–O bond becomes a double bond (N=O), and nitrogen's remaining two electrons form a lone pair on N. The nitrite ion is therefore represented by two equivalent resonance (canonical) Lewis structures — and — differing only in which oxygen carries the double bond, both c …