1. Hybrid Orbitals

2. Why Covalent Bonds Exist Atoms share electrons when their orbitals overlap When orbitals overlap, electrons are simultaneously attracted to both nuclei

3. Bond Length As atoms come closer, increasing electron density results in a decrease in potential energy of system As atoms become very close, electrostatic repulsion between nuclei increases Bond distance is a compromise between increased overlap drawing them together and increased repulsion pushing them apart There is an optimal bond distance where energy is lowest

5. Sigma Bond (σ) Covalent bond which the electron density is concentrated symmetrically along the internuclear axis Line joining the two nuclei passes through middle of overlap Could be two s orbitals overlap, two p orbitals overlap or an s and p overlap

7. Pi Bond (π) Overlap of orbital is perpendicular to line connecting nuclei Two p orbitals overlapping Since not a total overlap pi bonds tend to be weaker than sigma

8. Bond Types Single bonds are always sigma Double bonds consist of a sigma and a pi bond Triple bonds, sigma and two pi

9. Hybrid Orbitals Mixing of s and p orbitals creates hybrid orbitals CH 4 has four bonds coming from central atom Each bond is formed by overlap of an sp hybrid orbital

12. Types of Hybrids sp 3 hybrid – one s and three p orbital joined sp 2 hybrid – one s and two p orbitals sp hybrid – one s and one p orbital Hybrid orbital type accounts for observed geometry

14. Unshared Pairs Unshared pairs can occupy hybrid orbital NH 3 H 2 O

15. Predicting Hybrid Orbitals Draw structure Determine electron pair geometry Specify hybrid orbitals needed to accommodate the electron pairs

17. Examples What type of hybrid orbitals in –BeH 2 –BF 3 –NH 2 - –SF 4