Chapter 9 Flashcards
What principle is VSEPR theory based on?
Electrons have negative charges and repel each other. Pairs of electrons are arranged about the central atom in ways to minimize repulsion’s between the pairs.
What does VSEPR stand for?
Valence-shell electron-pair repulsion theory
What is electron-pair geometry?
The three-dimensional arrangement of bonding pairs and lone pairs of electrons about a central atom
What is meant by molecular geometry?
The 3D arrangement of the atoms in a molecule
Is electron-pair geometry and molecular geometry the same thing?
No, they may or may not be the same depending on the presence of lone pairs on the central atom. If there are no lone pairs then the electron-pair geometry and the molecular geometry is the same thing.
What is the steric number?
The sum of both the number of atoms bonded to a central atom and the number of lone pairs of e;extrinsic on the central atom
How do you calculate the steric number (SN)?
SN = (# of atoms bonded to the central atom) + (# of lone pairs on central atom)
In a covalent compound with a steric number of 2, what is it’s electron-pair geometry and molecular geometry?
In a covalent compound with a steric number of 3, what is it’s electron-pair geometry and molecular geometry?
In a covalent compound with a steric number of 4, what is it’s electron-pair geometry and molecular geometry?
In a covalent compound with a steric number of 5, what is it’s electron-pair geometry and molecular geometry?
In a covalent compound with a steric number of 6, what is it’s electron-pair geometry and molecular geometry?
How do we show 3D structures of a molecule on a 2D page?
We use a solid wedge to indicate a bond that comes out of a page and a dashed wedge to indicate a bond that goes behind the page and away from the viewer
How do double bonds affect the ideal bond angles of Lewis diagrams?
Double bonds exert greater repulsion than a single bond. So in CH2O the bond angle between the H’s would be less than 120 degrees
How does adding lone pairs to the central atom affect the molecular geometry?
- repulsion between lone pairs and bonding pairs is greater than the Repulsion between bonding pairs.
- repulsion caused by a lone pair is greater than that caused by a double bond
- repulsion caused by a double bond is greater than that caused by a single bond.
- two lone pairs of electrons on a central atom exert a greater repulsive force on the atom’s bonding pairs than does one lone pair
How does a molecule with a SN of 3 and no lone pairs compare to a molecule with a SN of 3 and 1 lone pair?
How does a molecule with at SN of 4 and no lone pairs compare to a molecule with a SN of 4 and 1 or 2 lone pairs?
How does a molecule with at SN of 5 and no lone pairs compare to a molecule with a SN of 5 and 1, 2 or 3 lone pairs?
How does a molecule with at SN of 6 and no lone pairs compare to a molecule with a SN of 6 and 1,2,3 or 4 lone pairs?
What is a bond dipole?
The separation of electrical charge created when atoms with different electronegativities form a covalent bond
The unequal distribution of bonding electrons that produces a partial negative charge in one region of the bond and a partial positive charge in the other.
What is a dipole moment (µ)
A measure of the degree to which a molecule aligns itself in a strong electric field. A quantitative expression of the polarity of a molecule.
A measure of the uneven distribution of electron density over the entire molecule
What is a permanent dipole?
Found in molecules with multiple polar bonds around a center atom. The bond dipoles may combine to give the molecule an pverall polarity.
What units are dipole moments expressed in?
debyes (D)
1 D = 3.34x10^-30 coulomb-meter
What is a key characteristic of all nonpolar substances?
molecular symmetry
becasue symmetric orientation of bond dipoles means the dipoles completely offset one another, producing dipole moments of zero.
