How do Atomic Orbitals Combine to From Molecular Orbitals and Create Molecular Bonds?
Please support my Patreon page (https://www.patreon.com/TheChemistryGuy). In this video we will examine hoe atomic orbitals form molecular orbitals and create molecular bonds. By looking at the periodic table we can determine orbital energies for the atomic orbitals. We can then fill it up from the bottom up for each element. This is known as the aufbau principle. Remember that whenever possible, at atom would like to look like a Noble Gas (He, Ne, Ar, …). In other words, it would like to either lose or gain electrons to form ions, or form bonds so that all electrons in its outer-most (or valence) shell are paired. For hydrogen, two Hydrogen atoms can come together, and you can either add the two 1s wavefunctions (orbitals) to form a sigma orbital (bonding) or subtract them to form a sigma-star orbital (antibonding). The sigma bonding orbital contains two electrons which both hydrogen nuclei can see. Therefore, both Hydrogen atoms would have a filled valence shell (n=1), like Helium. Two p-orbitals can also come together to form a pi bonding orbital and a pi-star antibonding orbital. . Carbon is a different matter. It has 2 electrons in the 2s orbitals and 2 electrons with the same spin in different 2p orbitals but needs all 4 electrons to be in different orbitals to form 4 bonds. This will effectively give it 8 electrons in the valence shell and will look somewhat like Neon. While mixing the 2s orbital with one or more 2p orbitals raises the energy of the 2s electrons, forming bonds with other atoms lowers the energy much more. The 2s orbital can mix with the empty 2p orbital to form two sp hybrid orbitals. The 2s orbital can mix with the empty 2p orbital and another 2p orbital to form 3 sp2 hybrid orbitals. The orbitals are 120o apart, all in the same plane. The remaining 2p orbital is perpendicular to this plane. The 2s orbital can also mix with all three 2p orbitals to form four sp3 hybrid orbitals. Each hybrid orbital is separated from all the other hybrid orbitals at an angle of 109.5o, and has a tetrahedral geometry, like a triangular pyramid composed of four equilateral triangles. Let’s look at the bonding in methane, CH4. The central Carbon makes four sigma bonds, one with each hydrogen. In general sigma bonds form first, and this requires an electron from the Carbon pairing with the electron in the hydrogen. Carbon therefore wants four unpaired electrons, so one electron goes in each of the sp3 hybrid orbitals. The Hydrogens form a sigma bond with each hybrid orbital of Carbon, and methane has a tetrahedral geometry. Chemistry is a notoriously difficult subject, so the purpose of this channel is to provide tutorials on a wide range of topics. Chemistry topics include balancing chemical reactions, the Ideal Gas Law, atomic structure of different elements and how this is reflected in the Periodic Table, and chemical bonding and how it determines the shape of molecules. As The Chemistry Guy I hope to be your go-to resource for all questions involving chemistry. #chemistry #scienceguy #chemistryguy
Please support my Patreon page (https://www.patreon.com/TheChemistryGuy). In this video we will examine hoe atomic orbitals form molecular orbitals and create molecular bonds. By looking at the periodic table we can determine orbital energies for the atomic orbitals. We can then fill it up from the bottom up for each element. This is known as the aufbau principle. Remember that whenever possible, at atom would like to look like a Noble Gas (He, Ne, Ar, …). In other words, it would like to either lose or gain electrons to form ions, or form bonds so that all electrons in its outer-most (or valence) shell are paired. For hydrogen, two Hydrogen atoms can come together, and you can either add the two 1s wavefunctions (orbitals) to form a sigma orbital (bonding) or subtract them to form a sigma-star orbital (antibonding). The sigma bonding orbital contains two electrons which both hydrogen nuclei can see. Therefore, both Hydrogen atoms would have a filled valence shell (n=1), like Helium. Two p-orbitals can also come together to form a pi bonding orbital and a pi-star antibonding orbital. . Carbon is a different matter. It has 2 electrons in the 2s orbitals and 2 electrons with the same spin in different 2p orbitals but needs all 4 electrons to be in different orbitals to form 4 bonds. This will effectively give it 8 electrons in the valence shell and will look somewhat like Neon. While mixing the 2s orbital with one or more 2p orbitals raises the energy of the 2s electrons, forming bonds with other atoms lowers the energy much more. The 2s orbital can mix with the empty 2p orbital to form two sp hybrid orbitals. The 2s orbital can mix with the empty 2p orbital and another 2p orbital to form 3 sp2 hybrid orbitals. The orbitals are 120o apart, all in the same plane. The remaining 2p orbital is perpendicular to this plane. The 2s orbital can also mix with all three 2p orbitals to form four sp3 hybrid orbitals. Each hybrid orbital is separated from all the other hybrid orbitals at an angle of 109.5o, and has a tetrahedral geometry, like a triangular pyramid composed of four equilateral triangles. Let’s look at the bonding in methane, CH4. The central Carbon makes four sigma bonds, one with each hydrogen. In general sigma bonds form first, and this requires an electron from the Carbon pairing with the electron in the hydrogen. Carbon therefore wants four unpaired electrons, so one electron goes in each of the sp3 hybrid orbitals. The Hydrogens form a sigma bond with each hybrid orbital of Carbon, and methane has a tetrahedral geometry. Chemistry is a notoriously difficult subject, so the purpose of this channel is to provide tutorials on a wide range of topics. Chemistry topics include balancing chemical reactions, the Ideal Gas Law, atomic structure of different elements and how this is reflected in the Periodic Table, and chemical bonding and how it determines the shape of molecules. As The Chemistry Guy I hope to be your go-to resource for all questions involving chemistry. #chemistry #scienceguy #chemistryguy