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Chemistry 1 > Chapter 6: Fundamentals of Chemical Bonding > Flashcards

Chapter 6: Fundamentals of Chemical Bonding Flashcards

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1
Q

Are molecules dynamic or static?

A

Dynamic

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2
Q

What are coulombic interactions>

A

The sum of the attractive energies for a stable molecule must exceed the sum of the repulsive energies

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3
Q

What is a covalent bond?

A

When electrons are shared between the nuclei

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4
Q

Bond length

A

The separation distance where the molecule is most stable

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5
Q

Bond energy

A

The strength of the bond

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6
Q

Polar covalent bond

A

The electron pair is unequally shared which results in partial charges

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7
Q

How do we determine which atom has a partial negative or partial positive charge?

A

Electronegativity (the ability to attract bonding electrons)
The bigger the difference in electronegativity, the more polar the bond

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8
Q

The further apart the atoms are on the periodic table, the ___ the difference in electronegativity

A

Larger

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9
Q

X< 0.5
0.5< X < 2
X> 2

A

Non-polar covalent bond
Polar covalent bond
Ionic bond

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10
Q

If all sides are full, 8 electrons are in the valence shell…this is called an____?

A

Octet

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11
Q

Do outer or inner atoms usually have the highest electronegativities?

A

Outer

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12
Q

How do you build a lewis structure?

A
  1. Count the valence electrons
  2. Assemble bonding framework
  3. Place three-non bonding pairs of electrons on each outer atom, except H
  4. Assign the remaining electrons to inner atoms
  5. Optimize electron configurations (double/triple bonds)
  6. Identify equivalent Lewis structures
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13
Q

Can elements in the 3rd period or higher have more than an octet? In the third row, which elements do we need to know?

A

Yes. If they have valence d orbitals.
Phosphorus (5 bonds)
Sulphur (6 bonds)
Chlorine (7 bonds)

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14
Q

What is formal charge?

A

The difference between the number of valence electrons in the free atom and the number of electrons assigned to that atom (valence electrons-1/2 bonding electrons + lone-pair electrons)

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15
Q

What are resonance structures?

A

When there is more than 1 valid Lewis structure

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16
Q

Always account for ____ before forming multiple bonds

A

Single bonds and lone pairs

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17
Q

What is the VSEPR theory?

A

Valence shell electron-pair repulsion theory

Electron pairs in the outer shell of an atom repel one another and end up as far away from each other as possible

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18
Q

What are hydrocarbons?

A

Molecules that contain only carbon and hydrogen

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19
Q

Structural isomers

A

Two or more compounds that have the same molecular formula but different arrangement of atoms

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20
Q

What makes up an electron group?

A

An electron group can be two electrons in a single bond, four electrons in a double bond, six electrons in a triple bond, a pair of non-bonding electrons, or a single electron

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21
Q

What is a ligand?

A

An atom or group of atoms bonded to an inner atom

22
Q

What is a steric number?

A

The sum of the number of ligands plus the number of lone pairs

23
Q

How to determine molecular shape?

A
  1. Determine the molecular shape
  2. Use the lewis structure to find steric numbers for inner atoms
  3. Determine the electron group geometries from the steric number
  4. Use the ligand count to derive molecular shapes from electron group geometries
24
Q

What molecular shape does silicon atoms always have?

A

Tetrahedral geometry

25
Q

What are the characteristics of steric numbers 2? (linear geometry)

A

A molecule with two ligands and no lone pairs

Bond angle = 180 degrees

25
Q

What are the characteristics of steric number 3 (Trigonal Plane)

A

A molecule with 3 ligands and no lone pairs

Bond angle = 120 degrees

26
Q

What are the characteristics of steric number 3? (Trigonal Planar)

A

Three ligands, no lone pairs

Common in carbon compounds that have double bonds. Each carbon atom has three ligands

27
Q

What are the characteristics of steric number 5? (Trigonal Bipyramid)

A

The five positions are not all equivalent
equatorial positions: 120 degrees
axial positions: 90 degrees

Lone pairs always occupy equatorial positions

28
Q

What are the molecular shapes of steric #6? (Octahedron)

A
  1. Octahedral (6 ligands, 0 lone pairs)
  2. Square pyramidal (5 ligands, 1 lone pair)
  3. Square planar (4 ligands, 2 lone pairs)
28
Q

What are the molecular shapes of trigonal bipyramidal?

A
  1. Trigonal bipyramidal (5 ligands, 0 lone pairs)
  2. Seesaw (4 ligands, 1 lone pair)
  3. T-shaped (3 ligands, 2 lone pairs)
  4. Linear (2 ligands, 3 lone pairs)
29
Q

What are the characteristics of steric number 6? (Octahedron)

A

All six positions of the octahedron are equivalent (90 degrees)

30
Q

Why do bond pairs in a molecule cause bond angles to be a few degrees smaller than predicted for symmetrical geometry?

A

Electron-electron repulsion generated by non-bonding pairs is always greater than that generated by bonding pairs

To reduce the overall electron-electron repulsion, the axial atoms move slightly away from the lone pair to give a bond angle slightly smaller

31
Q

How do you know if there’s a dipole moment?

A

Electronegativity differences and molecular geometry

The more polar the bond, the larger the molecular polarity (dipole moment, (u) )

32
Q

A molecule with polar bonds has no dipole moment if___?

A

A symmetrical shape causes bonds to cancel one another

33
Q

Symmetric geometries are disrupted when? (how are dipole moments created)

A
  1. When a lone pair replaces a bond, giving a molecule with a dipole moment
  2. Replacing one or more bonds to a different kind of atom introduces a dipole moment
34
Q

Trigonal planar electron groups are only non-polar if? What geometry is always polar?

A

The three electron groups are exactly the same (H-H-C-H)

Bent molecules are always polar

35
Q

Tetrahedral electron groups are only non-polar if? Which geometries are always polar?

A

The four electron groups are exactly the same (F-F-C-F-F)

Trigonal pyramidal and bent molecules

36
Q

Trigonal bipyramidal electron groups are non-polar only if? Which geometries are always polar?

A

The two axial electron groups are exactly the same and the three equatorial electron groups are exactly the same

Seesaw and T-shaped molecular geometries

37
Q

For linear molecular geometry, all three equatorial groups are lone pairs, so it is ______ if two axial groups are the same?

A

Non-polar

37
Q

Octahedral electron group geometry is non-polar only if? Which geometries are always polar?

A

If all 3 axial parts are symmetric and the same, and the three equitorial electron groups are exactly the same

Square pyramidal molecular geometries are always polar

38
Q

For square planar geometry in octahedron geometries, both groups in one linear part are lone pairs so _____ if the other two linear parts are symmetric

A

Non-polar

39
Q

What affects bond length?

A

Atomic radii
Bond order
Effective nuclear charges

40
Q

The bonds become _____ as the radii of the atoms become larger

A

Longer

41
Q

The smaller the principle quantum numbers of the valence orbitals, the _____ the bond

A

Shorter

42
Q

The higher the bond multiplicity, the _____ the bond

A

Shorter

43
Q

The higher the effective nuclear charge of the bonded atoms, the _____ the bond

A

Shorter

44
Q

The larger the electronegativity difference, the _____ the bond

A

Shorter

45
Q

Bond strength ____ as more electrons are shared between the atoms ( double and triple bonds)

A

Increases

46
Q

Bond strength ____ as the electronegativity difference between bonded atoms increases

A

Increases

47
Q

Bond energy ____ as bonds become longer

A

Decreases

Chemistry 1 (6 decks)

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