Chemistry Warm-up: 1. Pick up a set of the skeleton notes from the first lab table. 2. Complete the words of the week assignment. You need to have answers for Tuesday, Thursday and today. Today s : Draw Lewis Dot Structures for boron triiodide and oxygen difluoride.
Valence
Valence Shell
Valence Shell Electron
Valence Shell Electron Pair
Valence Shell Electron Pair Repulsion
Valence Shell Electron Pair Repulsion Theory
Valence Shell
Valence Shell Remember that the outermost energy level of an atom is referred to as the valence shell.
Valence Shell Remember that the outermost energy level of an atom is referred to as the valence shell. The electrons within this energy level, valence shell, are the only ones that are used in forming chemical bonds.
Electron Pair A lone pair of electrons is described as two electrons, on a central atom, that are not used within a chemical bond.
Electron Pair A lone pair of electrons is described as two electrons, on a central atom, that are not used within a chemical bond. N H H H Nitrogen has one LONE PAIR of electrons on the central atom.
Repulsion As you learned long ago, the two north ends of two different magnets will repel each other.
Repulsion As you learned long ago, the two north ends of two different magnets will repel each other. The same holds true for like charges within the atom. Lone pairs of electrons, on a central atom, will repel each other as well as the electrons within a bond to make the most stable arrangement for that molecule.
Repulsion As you learned long ago, the two north ends of two different magnets will repel each other. The same holds true for like charges within the atom. Lone pairs of electrons, on a central atom, will repel each other as well as the electrons within a bond to make the most stable arrangement for that molecule. N H H H That lone pair of electrons within the NH3 molecule occupy space and repel the electrons within the bonds causing the molecule to be shaped sort of like a tripod.
VSEPR Theory is based on the idea that the geometry of a molecule is determined primarily by repulsions among the pairs of electrons associated with a central atom. Only valence electrons of the central atom influence the molecular shape in a meaningful way.
There are some basic assumptions that must be considered: 1. Pairs of electrons in the valence shell of a central atom repel each other. 2. These pairs of electrons tend to occupy positions in space that minimize repulsion and maximize the distance of separation between them. 3. The valence shell is taken as a sphere with electron pairs localizing on the spherical surface at maximum distance from one another. 4. A multiple bond is treated as if it is a single electron pair and the two or three electron pairs of a multiple bond are treated as a single super pair.
There are five basic shapes of molecules that can be predicted using the above assumptions. They are: 1. Linear 2. Angular / V-shaped / Bent 3. Tetrahedral 4. Trigonal Planar and 5. Trigonal Pyramidal. For each of these we will follow the same format of shape, number of atoms bonded to the central atom, number of lone pairs of electrons on the central atom, and an example with a Lewis Dot Structure.
Example Lewis Dot Structure HBr (hydrogen monobromide) H Br Linear None (there is no central atom) # of atoms bonded to the central atom None (there is no central atom) # of lone pairs of electrons on the central atom
Example BeH2 (beryllium hydride) Lewis Dot Structure H Be H Linear Two None # of atoms bonded to the central atom # of lone pairs of electrons on the central atom
Example H2O (dihydrogen monoxide) Two Angular (V-shaped, Bent) Lewis Dot Structure H O H Two # of atoms bonded to the central atom # of lone pairs of electrons on the central atom
Example CH4 (methane or carbon tetrahydride) Four Tetrahedral Lewis Dot Structure H H C H H None # of atoms bonded to the central atom # of lone pairs of electrons on the central atom
Example BF3 (boron trifluoride) Three Trigonal planar Lewis Dot Structure F B F F None # of atoms bonded to the central atom # of lone pairs of electrons on the central atom
Example Lewis Dot Structure NH3 (ammonia or nitrogen trihydride) Trigonal H N H H pyramidal Three One # of atoms bonded to the central atom # of lone pairs of electrons on the central atom
Name the shape for each of the following molecules. A: B: C: D: