3.3-3.5 Flashcards
Important application of molecular shape research
Enzymes- large proteins that react with only specific molecules because of their shape. Catalyze specific reactions in living cells.
Linus Pauling’s main empirical work
X-ray analysis of crystals. The valence bond theory was created to explain what he observed in the laboratory. (extended the work of Gilbert Lewis)
What did Ronald Nyholm and Ron Gillespie create.
In 1957 they created VSEPR theory.
Stereochemistry
Study of the 3-D spatial configuration of molecules and how this affects their reactions.
VSEPR Theory
Valence-shell-electron-pair-repulsion theory. Pairs of electrons in valence shell of an atom stay as far apart as possible because negative charges repel each other. The type, number, and direction of bonds determine the shape of resulting molecule/ polyatomic ion.
In general formula, what do A, X, and E represent
A= central atom, X= bond pairs, E= lone pairs
Which electrons are important for molecular shape according to VSEPR theory
Valence electrons of the central atom(s)
How is molecular shape determined according to VSEPR theory
The positions of the electron pairs when they are a maximum distance apart.
Why does a trigonal pyramidal formula have an angle of 107.3 and not 109.5
There is a slightly stronger repulsion between the lone pair of electrons and the bonding pairs than between the bonding pairs. This causes bonding pairs to be pushed closer together.
What type of bond is strongest?
Multiple bonds (double, triple) are shorter and stronger than single bonds. They also react rapidly.
Polar molecule
A molecule in which the negative (electron) charge is not distributed symmetrically among the atoms making up the molecule.
Non polar molecule
Molecule with symmetrical electron distribution
What theories did Linus Pauling combine?
He combined valence bond theory and bond energy theory to create the concept of electronegativity. Pauling explained the polarity of a covalent bond as the difference in electronegativity of bonded atoms. Higher difference = higher polarity.
Nonpolar covalent bond
Bonded atoms have the same electronegativity and share electrons equally.
Polar covalent bond
Bonded atoms have different electronegativities. The higher the difference in electronegativity, the more polar the bond
What will happen when difference in electronegativity is very high?
The difference in attraction, combined with other factors, may transfer one or more electrons from one atom to the other, forming cations and anions. These ions will group together to form an ionic compound.
Bond dipole
The charge separation that occurs when electronegativity difference of two atoms shifts shared electrons, making one side of the bond positive and one negative. Arrow points from positive (low electronegativity) to negative (high).
Why can molecules with polar bonds be nonpolar?
If the bond dipoles balance each other producing a molecular dipole (vector sum) of zero, the molecule is non polar.
How does polarity of a molecule affect its solubility?
Polar compounds are soluble in polar solvents while nonpolar compounds are soluble in nonpolar solvents
Intermolecular forces
Forces of attraction and repulsion between molecules
Van der Waals forces
Attractive forces acting between molecules. In many substances, Van der Waals forces are a combination of many types of intermolecular forces.
Who suggested that there was a reason gases condense when cooled?
In 1873, Johannes Van der Waals suggested this. He assumed that molecules of gasses must have a small but definite volume, and the molecules must exert weak attractive forces on each other. (virgin)
What force is responsible for what can be physically observed about molecular substances , as well as physical behaviors?
Intermolecular forces. Ex. Crystalline structure, soluability
Dipole-dipole force
Attraction between any dipole and surrounding dipoles. Among the weakest intermolecular forces, strength determined by overall polarity of a molecule. Dipoles- oppositely charged sides of a molecule.