its professor Dave, let's talk about molecular geometry as we begin to learn more about molecules it's important to understand the way molecules are arranged in three-dimensional space because this will affect how the molecule does chemistry. a model we can use to analyze molecular geometry is called the VSEPR model which stands for valence shell electron pair repulsion this is how we will predict the shape of a molecule. atoms are surrounded by clouds of negatively charged electrons and when you have atoms in a molecule together, these electron clouds repel each other. because of this, a molecule will automatically adopt a particular geometry so as to allow all the atoms to be as far away from each other as possible think of these electron clouds as magnets of like charge. the closer you push them together the more potential energy they have. things want to be at the lowest energy possible so if you let go they will push apart, lowering their energies. atoms will do the same thing. take carbon dioxide for example. the carbon atom has two electron domains, or areas of electron density extending from it. in order to participate in these bonds the carbon takes an s orbital and a p orbital and hybridizes them forming sp hybridized molecular orbitals. for now we can just count the number of electrons domains and use that many atomic orbitals to describe the hybridization of the central atom in a molecule. for each energy level there is one s, three p's, and five d's so here we just need one s and one p for these two electron domains. anything that is sp hybridized is going to show linear electron domain geometry because the farthest these two oxygen atoms can be from each other while still being bound to carbon is this shape which involves a 180 degree bond angle. look at a molecule like BF3. boron has three valence electrons so it can make three bonds that means that there are three electron domains surrounding the boron atom. that makes the boron s, p, p sp2 hybridized. anything that is sp2 hybridized will exhibit trigonal planar electron domain geometry. this is the furthest the 3 fluorines can be from each other while connected to the boron. trigonal planar molecules have 120 degree bond angles. once we get to four electron domains around a central atom we will need to utilize the third dimension. the carbon in methane is sp3 hybridized so it has tetrahedral electron domain geometry. these 109.5 degree bond angles put the hydrogens as far away from each other as they can be, making a shape that would have four sides if we connected the points atoms with five electron domains are sp3d hybridized and have trigonal bipyramidal electron domain geometry. basically two pyramids connected at the base. these complexes have both 90 and 120 degree bond angles. and atoms with six electron domains are sp3d2 hybridized and have octahedral geometry resembling an eight sided figure. all the bond angles here are 90 degrees. so in order to figure out the electron domain geometry of a molecule you just count up the electron domains. the number will tell you the hybridization and therefore the geometry. besides covalent bonds to other atoms lone pairs also count as electron domains. take ammonia for example. the three hydrogens and one lone pair make nitrogen sp3 hybridized so it has tetrahedral electron domain geometry, but the lone pair doesn't take up as much space as a bond to another atom so it has a slightly different shape from methane, and we assign it a different molecular geometry. molecules that are sp3 hybridized but have one lone pair are said to have trigonal pyramidal molecular geometry. the oxygen atom in a water molecule is also sp3 hybridized because it makes two bonds and has two lone pairs for a total of four electron domains, but the two lone pairs mean this molecule has a bent molecular geometry it is very important to understand how molecules like carbon dioxide and water have completely different shapes even though they contain the same number of atoms. the lone pairs on oxygen are pushing away the electron clouds on the hydrogen just like an atom would which is why it has tetrahedral electron domain geometry but the shape or the molecular geometry is bent because the lone pairs don't take up as much space as a bond to another atom. in CO2, carbon doesn't have any lone pairs, just bonds to oxygen. so to summarize, the number of electron domains surrounding an atom, be they covalent bonds or lone pairs determines the hybridization of the central atom. the hybridization should contain as many letters as there are electron domains. the hybridization correlates with a particular electron domain geometry, and within each electron domain geometry there can be multiple molecular geometries as we replace bonds with lone pairs when asked to assign these geometries always start by drawing the correct lewis dot structure, and then just count up the electron domains let's check comprehension thanks 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