EXAM 2: 07 Molecular Structure

Question 1

Are electrons in covalent bonds always shared equally

Answer 1

No

Question 2

Which electron gives up its electron and which atom accepts one in ionic bonding

Answer 2

Gives up - from the left side of the periodic table
Accepts - right side of the periodic table

Question 3

Does electrostatic attraction increase or decrease the energy of a system

Answer 3

It lowers the energy or a system

Question 4

In covalent bonding is the energy of the system increased or decreased

Answer 4

Decreased as the shared electron pairs bonded to both nuclei lowers it

Question 5

What is polarity

Answer 5

Separation of electric charges leading to a molecule or its chemical groups having an electric dipole moment

Question 6

What is electronegativity

Answer 6

The tendency of an atom to attract electron density in the bond toward itself
- the tendency of an atom to donate or accept electron density within chemical bonds

Question 7

High electronegative atoms

Answer 7

Readily accept electron density, form negative ions

Question 8

Low electronegative atoms

Answer 8

Sometimes called electropositive, readily donate electron density and form positive ions

Question 9

What is a molecular compound

Answer 9

Made up of individual molecules that contain 2 or more atoms connected by a covalent bond

Question 10

Characteristics of molecular compounds

Answer 10

Low melting points and poor conductivity ( two nonmetals )

Question 11

What is a dipole moment

Answer 11

Experimental measure of the polarization of electron density in molecules

Question 12

What is polarity

Answer 12

Separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment

Question 13

What is a dipole

Answer 13

A molecule with one end having a partial negative charge and the other end having a partial positive charge; polar molecule

Question 14

What determines if the bonds are polar covalent, covalent or ionic

Answer 14

The electronegativity differences between bonded atoms

Question 15

What is a polar covalent bond

Answer 15

A covalent bond between atoms w/ different electronegativities; bonding electrons are shared unequally

Question 16

What bonds represent the extremes of bonding possibilities

Answer 16

Purely ionic bonds and nonpolar covalent bonds

Question 17

If the change in electronegativity is greater than 1.8

Answer 17

Full or almost full electron transfer, ionic solids

Question 18

If the change in electronegativity is less than 0.4

Answer 18

Nonpolar covalent

Question 19

As change in electronegativity increases…

Answer 19

So does polarity

Question 20

If the change in polarity is equal to 0

Answer 20

Nonpolar covalent

Question 21

Any molecule in which the enters of positive and negative charges do not coincide is a…

Answer 21

Polar molecule

Question 22

What are dipole-dipole interactions

Answer 22

Attractive forces that act between polar molecules

Question 23

Are dipole-dipole interactions stronger or weaker than ion-ion interactions

Answer 23

Weaker

Question 24

What is a nonpolar covalent bond

Answer 24

Equal sharing of electrons between two nuclei
- ex: diatomic elements (H-H)(Cl-Cl) also C-H

Question 25

What are polar covalent bonds

Answer 25

Unequal sharing of electrons between nuclei - one nuclei is tugging on the electron density in the bond more than the other - example: H-F, more electron density at F (partially negative) (C-O, O-H, N-H)

Question 26

What makes a bond polar, nonpolar or ionic

Answer 26

It comes down to electronegativity

Question 27

What is the difference between electronegativity and electron affinity

Answer 27

Electronegativity is the ability to attract electrons to itself in a chemical bond which electron affinityy is where an electron has been gained by an individual ion

Question 28

What do Lewis structures show

Answer 28

Atom connectivity and apportionment of all bonding and nonbonding electrons to individual atoms in molecules

Question 29

What is the central atom

Answer 29

The first atom listed, or the least electronegative

Question 30

What does it mean to be hypervalent

Answer 30

Exceed the valence rules, more than 8 electrons around them - must be from the 3rd period of the periodic table or below, and be large

Question 31

The lewis structures that best describe electron distribution in molecules have the _______ formal charges possible

Answer 31

Smallest

Question 32

What is the formula for formal charge

Answer 32

FC = Number of valence electrons - number of unpaired electrons and bonds

Question 33

What are the guidelines used in selecting the dominant structure (when comparing different Lewis structures)

Answer 33

- the dominant structure has the smallest charge separation, preferably with zero formal charges or the smallest possible formal charges - the positioning of the formal charges in the dominant structure is consistent with the relative electronegativities of atoms; the dominant structure should have negative formal charges on the most electronegative atoms, and positive charges on the least electronegative atoms

Question 34

What are delocalized electrons

Answer 34

Electrons that are spread over a number of atoms in a molecule, rather than localized between a pair of atoms

Question 35

What is a resonance structure

Answer 35

Two or more equally valid Lewis structures for a single molecule that differ only in the apportionment of electrons; must have the same arrangement of atomic nuclei

Question 36

What does localized mean

Answer 36

Describes electrons that are limited to motions in limited space - ex: residing in a small orbital or shared between two specific atoms

Question 37

What is delocalized bonding

Answer 37

A type of bonding in which a bonding pair of electrons is spread over a number of atoms rather than localized between two

Question 38

Cyclic delocalization of bonding electrons may lead to _______ stability

Answer 38

Increased

Question 39

What are the three categories off octet rule expectations

Answer 39

1. Molecules or polyatomic ions with an odd number of electrons 2. Molecules or polyatomic ions with atoms that have fewer than an octet of valence electrons 3. Molecules or polyatomic ions in which atoms have more than an octet of valence electrons

Question 40

What are radicals

Answer 40

A chemical species, an atom or an ion with an odd number of electrons - generally very reactive