Chapter 9 (part 2): Chemical Bonding I: Lewis Theory Flashcards Preview

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Flashcards in Chapter 9 (part 2): Chemical Bonding I: Lewis Theory Deck (43):
1

Bond energies are always ____ because it always _____ energy to break a bond

Positive
Takes

2

A bond is stronger than another when it requires ____ energy to break it (ie. _____ bond energy)

More
Greater

3

A strong and stable bond will cause a molecule to be relatively ______

Inert

4

What two things do bond energies depend on?

The kind of atoms involved in the bond and the type of bond (single, double, triple)

5

The bond energy for tripe bond is _____ than the bond energy for double bonds which is ____ than the bond energy for single bonds

Greater
Greater

6

Bond energies can be used to estimate _____ change of a reaction

Enthalpy

7

When bonds break the process is ____ so bond energy is _____

Endothermic
Positive

8

When bonds form the process is _____ so bond energy is _____

Exothermic
Negative

9

A reaction is Exothermic when ____ bonds are broken and ____ bonds are formed

Weak
Strong

10

A reaction is endothermic when _____ bonds break and ____ bonds form

Strong
Weak

11

Breaking a chemical bond always _____ energy

Requires

12

Forming a chemical bond always _____ energy

Energy

13

Define bond length

The average length of a bond between two particular atoms in a variety of compounds

14

Bond lengths depend on

The kind of atoms involved in the bond and the type of bond (single, double, triple)

15

Define bond stretching vibration (or stretching vibration)

A molecular motion in which a bond stretched and then contracts

16

For bond vibrations to take place, energy much be ______ to the molecule

Supplied

17

Energy that cause bond vibrations can originate from.....

Molecular collisions or from the absorption of electromagnetic radiation in the infrared region

18

Why is energy that cause bond vibrations specifically cause by the infrared region of the electromagnetic spectrum and not other regions?

Because the infrared frequency range of electromagnetic radiation corresponds to the energies of molecular (E =hv)

19

Define infrared (IR) absorption spectroscopy

The measurement of molecular absorption of infrared frequency radiation to give information about molecular structure

20

Define wavenumber

The reciprocal of wavelength

21

In infrared absorption spectroscopy ______ is determined not the wavelength.

Wavenumber

22

The higher the wave number, the ____ the energy of light that was absorbed

Greater

23

As bond strength increases then the wavenumber value of absorption ______

Increases

24

Define polar covalent bond

A covalent bond between two atoms with significantly different electronegativities, resulting in an uneven distribution of electron density

25

Most covalent bonds between dissimilar atoms are actually _____ _____

Polar covalent

26

Define electronegativity

The ability of an atom to attract electrons to itself in a covalent bond

27

Electronegativity ___ across a row

Increases

28

Electronegativity _____ down a column

Decreases

29

Fluorine is the _____ electronegative atom

Most

30

Francium is the _____ electronegative atom

Least

Also Is sometimes called the most electropositive

31

Electronegativity follows what rule of thumb perfectly

Righter tighter lower loser

32

What does the degree of polarity in a chemical bond depend on?

The electronegative difference between the two bonding elements (sometimes abbreviated delta EN)

33

The greater the electronegativity difference, the more ____ the bond

Polar

34

If two elements with identical electronegativities form a covalent bond, they share the electrons equals, and the bond is purely _____ or ____ ____

Covalent
Non polar

35

When the electronegativity difference is small (0-0.4) the bond type is ...?

Covalent

36

When the electronegativity difference is intermediate (0.4-2.0) the bond type is ...?

Polar covalent

37

When the electronegativity difference is large (2.0 and up) the bond type is ...?

Ionic

38

How do you quantify the polarity of a bond?

By the size of its dipole moment

39

Define dipole moment

A measure of the separation of positive and negative charge in a molecule

40

What unit is commonly used for reporting dipole moments?

The Debye (D)
(1D = 3.34 x 10^-30 C•m)

41

Define percent ionic character

The ratio of a bonds actual dipole moment to dipole moment it would have if the electron were transferred completely from one atom to the other, multiplied by 100%

42

In general bonds with greater than ____ ionic character are referred to as ionic bonds

50%

43

Define bond energy

The energy required to break 1 mole of the bond in the gas phase