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If you memorize which molecules are the ones without lone pairs, then it is fairly easy to intuit which molecules are the ones with one less atom and a lone pair instead. (identical electron arrangement, different molecular shape) This is the method that I usually use.
You can determine the VSEPR formula (AXE) by looking at a molecule. For example, water is sp3 hybridized with AX2E2. This is because there are 2 bonded pairs (between each H and the O) and 2 lone pairs (on the oxygen). If you know an example of a molecule for each molecular geometry or are trying to determine AXE for a molecule, I would suggest drawing the LDMS and counting bonded pairs and lone pairs. If you are determining AXE for a molecule you can do that just by drawing the LDMS.
When writing the VSEPR formula, you begin with A which is the central atom. And then E and the subscript number will depend on the amount of "things" it's attached to, regardless of bonds. Then you'd finish with E and the subscribe number will depend on the amount of LONE PAIRS. We count everything in pairs, not individually. Hope this helps!
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