Molecular orbitals Flashcards
Instead of VSEPR, what can provide an explanation for more complex molecules?
molecular orbital theory
When do molecular orbitals form?
when atomic orbitals combine
What is the number of molecular orbitals formed equal to?
the number of atomic orbitals that combine
What does the combination if 2 atomic orbitals result in?
the formation of a bonding molecular orbitals and an antibonding orbital
the bonding molecular encompasses both nuclei
what is the basis of bonding between atoms?
the attraction of the positively charged nuclei and the negatively charged electrons in the bonding molecular orbital
how many electrons can each molecular orbitals hold
max 2
describe the bonding molecular orbital in a non-polar covalent bond
symmetrical about the midpoint between two atoms
what do polar covalent bonds result from? and which atom has a greater share of the bonding electrons?
bonding molecular orbitals that are asymmetric about the midpoint between 2 atoms
the atom with the greater value for EN has the greater share of bonding electrons
What is an example of an extreme case of asymmetry in a bond?
ionic compounds, with the bonding molecular orbitals being almost entirely located around just one atom, resulting in the formation of ions
how are sigma bonds molecular orbitals/sigma bonds formed?
(single bond) (whistle greek sign)
end-on overlap of atomic orbitals along the axis of the covalent bonds
how are pi molecular orbitals/pi bonds formed?
(double bond) (pi greek symbol)
form by side-on overlap of parallel orbitals that lie perpendicular to the axis of the covalent bond
what can the electronic configuration of an isolated carbon atom not explain?
what can explain it?
-the number of bonds formed by the carbon atoms in molecules
-hybridisation
What is hybridisation?
the process of mixing atomic orbitals within an atom to generate a set of new atomic orbitals called hybrid orbitals. These hybrid orbitals are degenerate.
Hybridisation bonding in alkanes
-the 2s orbital and the 3 2p orbitals of carbon hybridise to form 4 degenerate sp3 hybrid orbitals
-these adopt a tetrahedral arrangement
-the sp3 hybrid orbitals overlap end-on with other atomic orbitals to form sigma bonds.
hybridisation bonding in alkenes
-the 2s orbital and 2 of the 2p orbitals hybridise to form 3 degenerate sp2 hybrid orbitals
-these adopt a trigonal planar arrangement
-the hybrid sp2 orbitals overlap end-on to form sigma bonds
-the remaining 2p orbitals on each carbon atom of the double bond is unhybridised and lies perpendicular to the axis of the sigma bond
-the unhybridised p orbitals overlap side-on to form pi bonds
hybridisation bonding in benzene and other aromatic systems
-sp2 hybridisation
-the 6 atoms in benzene are arranged in a cyclic structure with sigmas bonds in between the carbon atoms
-the unhybridised p orbitals on each carbon atom overlap side-on to form a pi molecular system, perpendicular to the plane of the signa bonds.
-this pi molecular system extends across all 6 carbon atoms
-the electrons in this system are delocalised
hybridisation bonding in alkynes
-sp hybridisation
-the 2s orbital and one 2p orbitals of carbon hybridise to form two degenerate hybrid orbitals
-these adopt a linear arrangement.
-the hybrid sp2 orbitals orbitals overlap end-on to form sigma bonds
-the remaining 2 2p orbitals on each carbon atom lie perpendicular to each other and to the axis of the sigma bond
-the unhybridised p orbitals overlap side-on to firm 2 pi bonds
How is the energy to promote an electron overcome?
by -a better shape for forming bonds
-the energy released when forming new bonds
what does an sp3 hybrid orbitals look like?
p orbital with one small side and one big side
what is a difference between sigma and pi bonds
sigma bonds are rotatory (allow rotation around the axis of the sigma bond
bond angle in ethene
120 degrees
what type of molecule is ethene?
planar
Is a C=C double bond or a C-C single bond shorter?
C=C double bond
