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Chem 103 > Ch 10 > Flashcards

Ch 10 Flashcards

1
Q

Lewis structures

A

show us how atoms are bonded to each other. They can be used to predict molecular shapes, bond strength and bond length.

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2
Q

Covalent Bonds

A

Formed when two (or more) nonmetals share valence electrons in order to obey the octet rule.

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3
Q

Single bond

A

two atoms share a pair of electrons between them (2 shared electrons = 1 bond)

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4
Q

Electron-dot formulas show

A
  • The order of bonded atoms in a covalent compound.
  • The bonding pairs of electrons between atoms.
  • The unshared (lone) valence electrons.
  • A central atom with an octet.
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5
Q

Double bond

A

two atoms share 2 pairs of electrons between them (4 shared electrons = 2 bonds) in order to obey the octet rule

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6
Q

Triple bond

A

two atoms share 3 pairs of electrons between them (6 shared electrons = 3 bonds)

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7
Q

In a single bond

A

One pair of electrons is shared.

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8
Q

In a double bond

A

Two pairs of electrons are shared

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9
Q

In a triple bond

A

Three pairs of electrons are shared

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10
Q

Bond Length

A
  • Distance between 2 nuclei

- Triple bond < Double Bond < Single Bond

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11
Q

Bond Strength

A
  • Energy required to separate 2 nuclei

- Triple bond > Double Bond > Single Bond

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12
Q

Coordinate Covalent Bonds

A

bond in which there is an uneven contribution of the shared electron pairs.

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13
Q

As long as all the atoms in your molecule are satisfied under the octet rule (exception is H with only 2 electrons),

A

then you have an acceptable Lewis Dot Structure

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14
Q

Guide to Writing Electron-Dot Formulas

A

STEP 1 Determine the arrangement of atoms. (usually the first one in the formula unless the first atom is H)

STEP 2 Add the valence electrons from all the atoms.

STEP 3 Attach the central atom to each bonded atom using one pair of electrons.

STEP 4 Add remaining electrons as lone pairs to complete octets (2 for H atoms).

STEP 5 If octets are not complete, form one or more multiple bonds.

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15
Q

Resonance structures are

A
  • Two or more electron-dot formulas for the same arrangement of atoms
  • Related by a double-headed arrow
  • Written by changing location of a double bond from the central atom to a different attached atom
  • Sometimes written as a hybrid resonance structure
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16
Q

Molecular Shape

A
  • Lewis Structures tell us how atoms are connected in a covalent molecule or ion
  • They can also be used to predict molecular shape
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17
Q

Molecular shape

A
  • determines how molecules function.

- is essential to drug design and other biochemical processes

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18
Q

In order to predict molecular shape, we assume that electron groups repel each other (because they are all negatively charged).

A

Therefore, the molecule adopts whichever 3D geometry minimized this repulsion

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19
Q

VSEPR

A

Valence Shell Electron Pair Repulsion theory

20
Q

Molecules adopt shapes that

A

minimize the repulsion between electron groups/domains

21
Q

What is an electron group/domain?

A

A collection of valence electrons present in a localized region about the central atom in a molecule

22
Q

There are two kinds of electron groups/domains

A
  • A pair of nonbonding electrons

- An area where there are bonding electrons (it doesn’t matter if the bond is a single, double or triple bond)

23
Q

Determining Molecular Shape

A

First, draw the Lewis Structure for the compound

There are two important features of Lewis Structures that you must recognize:

a. The number of ATOMS bonded to the central atom (this is the number of bonding electron groups/domains)
b. The number of PAIRS of nonbonding electrons on the central atom (this is the number of nonbonding electron groups/domains

24
Q

Electronegativity

A

A measure of the relative attraction that an atom has for the shared electrons in a bond

25
Q

Trends in electronegativity

A

Electronegativity values increase from left to right on the periodic table

Electronegativity values increase from the bottom to the top of the periodic table

26
Q

Electronegativity difference: 0.0 to 0.4

A

nonpolar covalent.

27
Q

Electronegativity difference: 1.8 or greater

A

bond considered ionic.

28
Q

Electronegativity difference:greater than 0.4 or less than 1.8

A

bond considered polar covalent

29
Q

Polar covalent bonds

A

A covalent bond in which there is unequal sharing of electrons between two atoms

30
Q

Nonpolar covalent bonds

A

A covalent bond in which there is equal sharing of electrons between two atoms

31
Q

Bond Polarity

A

a measure of the degree of inequality in the sharing of electrons between two atoms in a chemical bond

32
Q

If a bond is between two of the same kinds of atoms

A

It will be NONpolar

33
Q

If a bond is between two different atoms

A

It will be polar to some degree (more so the further apart the two atoms are on the periodic table)

34
Q

Polar Molecule

A

A molecule in which there is an unsymmetrical distribution of charge

35
Q

Molecular Polarity

A

A measure of the degree of inequality in the attraction of bonding electrons to various locations within a molecule

36
Q

Why do we care if the molecule is polar?

A

Polar molecules dissolve in polar solvents

Nonpolar molecules dissolve in nonpolar solvents

37
Q

Molecules with the following geometries are nonpolar (if there is at least one polar bond in the molecule):

A 
Linear (with 2 of the same atom bonded to a central atom)
Trigonal Planar (with 3 of the same atom bonded to a central atom)

Tetrahedral (with 4 of the same atom bonded to a central atom)

Trigonal bi-pyramidal (with 5 of the same atom bonded to a central atom)

Octahedral (with 6 of the same atom bonded to a central atom)

Square planar (with 4 of the same atom bonded to a central atom)

38
Q

Covalent or ionic bonds that hold a molecule together are

A

intramolecular forces

39
Q

The attraction between molecules is an

A

intermolecular force

40
Q

Intermolecular forces are much ___than intramolecular forces

A

weaker

41
Q

There are different intermolecular forces

A

Dipole-Dipole Forces

Hydrogen “Bonds”

London Dispersion Forces

42
Q

London Dispersion Forces

A

Formed between adjacent neutral molecules

Weak attractions between nonpolar molecules.

Caused by temporary dipoles that develop when electrons are not distributed equally.

Increase with size of atoms or molecular weight of molecules

43
Q

Intramolecular Bonds

A

Ionic Bonds

44
Q

Intermolecular Forces

A

Hydrogen “Bonds”

45
Q

Hydrogen Bonds

A

Unusually strong dipole-dipole interactions that occur between molecules with H-N, H-O, or H-F covalent bonds and a lone pair of electrons on another small, electronegative atom

Chem 103 (13 decks)

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