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Chem 115 > Chapter 9 > Flashcards

Chapter 9 Flashcards

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1
Q

What principle is VSEPR theory based on?

A

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.

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2
Q

What does VSEPR stand for?

A

Valence-shell electron-pair repulsion theory

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3
Q

What is electron-pair geometry?

A

The three-dimensional arrangement of bonding pairs and lone pairs of electrons about a central atom

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4
Q

What is meant by molecular geometry?

A

The 3D arrangement of the atoms in a molecule

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5
Q

Is electron-pair geometry and molecular geometry the same thing?

A

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.

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6
Q

What is the steric number?

A

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

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7
Q

How do you calculate the steric number (SN)?

A

SN = (# of atoms bonded to the central atom) + (# of lone pairs on central atom)

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8
Q

In a covalent compound with a steric number of 2, what is it’s electron-pair geometry and molecular geometry?

A
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9
Q

In a covalent compound with a steric number of 3, what is it’s electron-pair geometry and molecular geometry?

A
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10
Q

In a covalent compound with a steric number of 4, what is it’s electron-pair geometry and molecular geometry?

A
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11
Q

In a covalent compound with a steric number of 5, what is it’s electron-pair geometry and molecular geometry?

A
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12
Q

In a covalent compound with a steric number of 6, what is it’s electron-pair geometry and molecular geometry?

A
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13
Q

How do we show 3D structures of a molecule on a 2D page?

A

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

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14
Q

How do double bonds affect the ideal bond angles of Lewis diagrams?

A

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

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15
Q

How does adding lone pairs to the central atom affect the molecular geometry?

A
  • 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
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16
Q

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?

A
17
Q

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?

A
18
Q

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?

A
19
Q

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?

A
20
Q

What is a bond dipole?

A

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.

21
Q

What is a dipole moment (µ)

A

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

22
Q

What is a permanent dipole?

A

Found in molecules with multiple polar bonds around a center atom. The bond dipoles may combine to give the molecule an pverall polarity.

23
Q

What units are dipole moments expressed in?

A

debyes (D)

1 D = 3.34x10^-30 coulomb-meter

24
Q

What is a key characteristic of all nonpolar substances?

A

molecular symmetry

becasue symmetric orientation of bond dipoles means the dipoles completely offset one another, producing dipole moments of zero.

25
Q

what is valence bond theory?

A

a quantum mechanics-based theory of bonding that incorporates the assumption that covalent bonds form when half-filled orbitals on different atoms overlap or occupy the same region in space.

26
Q

what is a sigma (σ) bond?

A

a covalent bond to which atomic orbitals on adjoining atoms occupy the same region or space.

27
Q

What is a pi (π) bond?

A

A covalent bond in which electron density is greatest around - not along - the bonding axis. It forms from side-on overlap of two parallel p orbitals.

Chem 115 (5 decks)

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