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Types of formulas

Types of formulas. Molecular formula = PH 3 .. Lewis structure = . P . .. Structural formula = H - P – H I H. Hints for finding structural formulas.

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Types of formulas

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  1. Types of formulas • Molecular formula = PH3 .. • Lewis structure = . P . .. • Structural formula = H - P – H I H

  2. Hints for finding structural formulas • Decide if each atom is a terminal or center atom. • The true center atom is usually furthest left on the periodic table. • Add up the total number of valence electrons. • Fill in bonding pairs on trial structure • Count electrons left • Fill in lone pairs & check for electrons left • Adjust structure by adding double or triple bonds

  3. Examples from 9.3 • NH3 • CO2 • PO4-3

  4. Resonance Structures • Occurs when a molecule has a double & single bond • More than 1 Lewis structure possible • Only the bonds move, not atoms • Ex: NO3-1 • Molecule is really an average of all the possibilities • Bond length is like a 1.5 bond

  5. Check for understanding • Draw Lewis structures for : CO3-2 S2O3 Which one has resonance? Which one does not show resonance?

  6. Octet Rule Rebels • Molecules with an odd number of valence electrons • Molecules that form with fewer than 8 valence e- (B is a common rebel – often go on & form coordinate covalent bonds) • Molecules that form with more than 8 valence electrons (expanded octet) – uses d orbitals to do this, so period 3 or >. • All 3 types tend to be reactive & unstable.

  7. Structures for rebels • Draw structures for: ClO2 NO BI3 BOBr SF6 XeF4

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