Hybrid Orbitals: atomic orbitals formed by blending different orbitals together Just like with other hybrids, the characteristics of the hybrid orbitals will depend upon the traits of the ‘parent’ orbitals.

Consider carbon… How many valence electrons does carbon have?4 According to its electron dot structure, how many unpaired electrons does carbon have? C What does carbon’s orbital filling diagram look like? 1s 2 2s 2 2p 2 Atomic carbon only has 2 upaired electrons! In order to form chemical bonds, carbon’s atomic orbitals must hybridize to form molecular orbitals.

+ one s orbital one p orbital two sp hybrid orbitals (AX 2 ) one s orbital two p orbitals three sp 2 hybrid orbitals (AX 3 ) + one s orbital three p orbitals four sp 3 hybrid orbitals (AX 4 ) +

O HH Sigma bonding When two atomic orbitals (hybridized or not) overlap end-on, they form a single sigma bond. + H  bond AX 2 E O H H sp 3 + s  bonds HH

Pi bonding When two atomic orbitals overlap in a side-to-side fashion, they form a pi bond. Orbitals that form pi bonds are usually NOT hybridized. O O  bond  bond Each oxygen had three sp 2 hybrid orbitals and one p orbital. The lone pairs are in sp 2 orbitals, and the  bond is formed by the overlap of two sp 2 orbitals. One unhybridized p orbital results in one pi bond. A sigma and a pi bond form a double bond.

N N  bond  bond 2s Multiple pi bonds Each nitrogen atom had two sp 2 orbitals and two p orbitals. The lone pairs went into an sp 2 orbital on each nitrogen. The  bond was formed by the overlap of the remaining sp 2 orbitals. The two  bonds were formed by the overlap of the two p orbitals.

Resonance Structures Draw the stick structure for CO 3 2- AX 3 so sp 2 hybrid. 2- Draw the resonance structures for SO 4 2- C O O O 2- S O O O O S O O O O S O O O O AX 4 so sp 3 hybrid. 2- C O O O C O O O S O O O O : equivalent Lewis dot structures

Polarity in bonding In covalent bonds, electrons aren’t always shared equally between the two nuclei. This is because some elements have a greater affinity for electrons than others. Electronegativity: Ability of an atom to attract electrons when in a molecule.

When electrons in a covalent bond are concentrated near one of the nuclei, the bond is POLAR. HF Polar bond HHNonpolar bond If the electrons are shared equally between the nuclei, the bond is NONPOLAR. ++ --

Because of the bent structure of water, water is a polar molecule. O H H Use arrows along the bonds to indicate the direction of the ‘pull’ on the electrons in the bond (the dipole moment). A plus-sign on the tail of the arrow shows that the bond is more positive at that end Both bonds in water are polar. How does this affect the polarity of the molecule? Add the two vectors (the arrows) together to find the net polarity (dipole moment) of the molecule

All of the bonds in CCl 4 are polar. Is this molecule polar? C Cl Since the molecule is symmetrical, all of the dipoles along the bonds cancel each other out. CCl 4 is a nonpolar molecule and has no net dipole moment.

Are these planar molecules polar or nonpolar? B F F F B F F H B H H H Are these linear molecules polar or nonpolar? OC OCO SCO nonpolarpolarnonpolar polarnonpolarpolar