Chapters 7 and 8. Chemical bonding. Valence Electrons. Elements with similar chemical behavior have the same number of valence electrons.
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Br: [Ar]4s23d10 4p5 Bromine has 7 valence electrons
Br: [Ar]4s2 3d10 4p5
Coordination Number = The number of ions of opposite charge surrounding the ion in a crystal.
Know that metals are arranged in crystalline structures, but do not worry about the arrangement of these structures: face-centered, body-centered, hexagonal.
Def: A condition when more than one valid Lewis structure can be written for a molecule or ion.
Too few electrons surrounding the central atom (ex: BH3)
Boron will not have a full octet, only 6 electrons. It can only achieve a full octet when another atom shares an entire pair of electrons with it (Coordinate covalent bonding)
Too many electrons surrounding the central atom (ex: PCl5)
An odd number of electrons
Predict the location of atoms
If there are more than two atoms, place the least electronegative atom in the center and surround it by the remaining atoms.
Hydrogen is always terminal (outside) because it can only make one bond
Determine the total number of electrons if each atom had a full set of valence electrons (2 for H, 8 for all others)
Add up the number of valence electron that you have to work with
Subtract total valence electrons from total electrons and divide by two. This is the number of bonding pairs that are needed to put together the molecule.
Connect the atoms with the number of bonds that you calculated above
Add lone pairs where needed so that each atom has a full octet (except for hydrogen which can only have two electrons)
Polyatomic ions are a cluster of non-metals that carry a charge.
To draw the structure of a polyatomic ion, follow the procedure for drawing ordinary molecules but add or subtract the number of electrons gained or lost to the total number of valence electrons in your structure as indicated by the charge on the ion.
Valence Shell Electron Pair Repulsion – minimizes the repulsion of shared and unshared pairs of electrons around the central atom.
The shape of a molecule determines many of its physical and chemical properties.
The VSEPR is based on the arrangement of bonding and lone electrons around a central atom to minimize repulsion.
The repulsion of electrons creates a specific bond angle between a central atom and two terminal atoms.
Lone pairs of electrons occupy more space than bonding pairs of electrons
Recall: Electronegativity is the ability of an atom to attract an electron.
Bond Type Difference
Non-polar Covalent 0-0.4
Polar Covalent 0.5-2.0
Molecules are either polar or non-polar
Both polar and non-polar molecules may contain polar bonds. What determines whether
a molecule is polar or non-polar is the symmetry of the molecule
VSEPR shapes that can demonstrate symmetry are:
Linear Trigonal Planar Tetrahedral