Molecular Geometry & Bonding Theories

Molecules have shapes and sizes that are defined by the ___________________ and ___________________ between the nuclei of atoms. Shape and size determine the properties of that substance.

Bond angles determine the molecular shape along with bond lengths. Molecular Shapes Lewis shape just gives ___________________. The Lewis structure helps us to begin to see the ___________________ shape Bond angles determine the molecular shape along with bond lengths. 3-D arrangement

Lewis Symbols Lewis structures show the ___________________. Maximum of ___________________ electrons Deals with the valence electrons Highest energy level, ___________________ sublevels

Lewis Structure Sulfur has 6 valence electrons Dots around the 4 sides of an atom represent the valence electrons. 2 electrons on a side – giving a possible 8 ___________________– atoms tend to gain or lose electrons, or share, to achieve 8 valence electrons (an octet)

Covalent Bonding Sharing of ___________________ between atoms of elements Simplest covalent bond – H2

Lewis Structures A dash, “—” represents a shared pair of ___________________

Double bonds represent ___________________ of electrons

Triple bonds represent ___________________ of electrons.

Drawing Lewis Structures of Compounds 1. Sum the valence electrons from all atoms P = 5 x 1 = 5 Cl = 7 x 3 = 21 26 valence electrons PCl3

2. Write the symbols for the atoms to show which atoms are attached to which and attach them (using a dash) Central atom is generally the less electronegative atom

3. Complete the octets around the atoms bonded to the central atom. Keep track of your electrons = 24 e-

4. Place any leftover electrons on the central atom.

5. If there are not enough electrons to give the central atom an octet, try multiple bonds.

(b) Draw the Lewis structure. (a) How many valence electrons should appear in the Lewis structure for CH2Cl2? (b) Draw the Lewis structure. Answers: (a) 20, (b)

Draw the Lewis structure for (a) C2H4.

VSEPR Model Valence Shell Electron Pair Repulsion model Is based on the number of regions of high electron density around a central atom. Can be used to predict structures of ___________________ or ions that contain only non-metals by minimizing the electrostatic ___________________ between the regions of high electron density. can also be used to predict structures of molecules or ions that contain multiple bonds or unpaired electrons.

Predicting the VSEPR Model Sketch the Lewis Structure Determine the molecular arrangement. Calculate the electron ___________________ around the central atom. Electron domain is the ___________________ domain around the central atom Double bonds & triple bonds count as 1 electron domain.

Bonding Pair Nonbonding Pair Electrons that are ___________________ Lone pairs of ___________________

O ─ O = O 2 bonding domains 1 nonbonding domain . . . . : . . . . . .

Molecular geometry is the arrangement of ___________________ in space. The best arrangement of a given number of electron domains is the one that will ___________________ the repulsion among them.

Molecular Geometry ___________________ of only the atoms of the molecule or ion Need to know the number of ___________________ and ___________________ pairs of electrons Draw the Lewis structure to determine the bonding and nonbonding pairs of electrons

Effect of Nonbonding Electrons on Bond Angles As the number of ___________________ electrons increases, the bond angle decreases. Nonbonding pairs of electrons experience less nuclear attraction because the domain spreads out which compresses the angles ___________________ represent larger domains Because of the higher electronic charge, it acts almost like a nonbonding pair of electrons

Nonbonding pairs of electrons will ___________________ the angles.

In general, electron domains for multiple bonds exert a greater repulsive force on adjacent electron domains than do electron domains for single bonds.

Molecules with Expanded Valence Shells Molecules with five or six electron domains around the central atom Trigonal bipyramidal Octahedral

Shapes of Larger Molecules Find the individual shapes of all the central atoms