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CHEM110 > EXAM 2: 07 Molecular Structure > Flashcards

EXAM 2: 07 Molecular Structure Flashcards

1
Q

Are electrons in covalent bonds always shared equally

A

No

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2
Q

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

A

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

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3
Q

Does electrostatic attraction increase or decrease the energy of a system

A

It lowers the energy or a system

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4
Q

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

A

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

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5
Q

What is polarity

A

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

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6
Q

What is electronegativity

A

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

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7
Q

High electronegative atoms

A

Readily accept electron density, form negative ions

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8
Q

Low electronegative atoms

A

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

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9
Q

What is a molecular compound

A

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

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10
Q

Characteristics of molecular compounds

A

Low melting points and poor conductivity ( two nonmetals )

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11
Q

What is a dipole moment

A

Experimental measure of the polarization of electron density in molecules

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12
Q

What is polarity

A

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

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13
Q

What is a dipole

A

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

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14
Q

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

A

The electronegativity differences between bonded atoms

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15
Q

What is a polar covalent bond

A

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

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16
Q

What bonds represent the extremes of bonding possibilities

A

Purely ionic bonds and nonpolar covalent bonds

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17
Q

If the change in electronegativity is greater than 1.8

A

Full or almost full electron transfer, ionic solids

18
Q

If the change in electronegativity is less than 0.4

A

Nonpolar covalent

19
Q

As change in electronegativity increases…

A

So does polarity

20
Q

If the change in polarity is equal to 0

A

Nonpolar covalent

21
Q

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

A

Polar molecule

22
Q

What are dipole-dipole interactions

A

Attractive forces that act between polar molecules

23
Q

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

A

Weaker

24
Q

What is a nonpolar covalent bond

A

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

25
Q

What are polar covalent bonds

A

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)

26
Q

What makes a bond polar, nonpolar or ionic

A

It comes down to electronegativity

27
Q

What is the difference between electronegativity and electron affinity

A

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

28
Q

What do Lewis structures show

A

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

29
Q

What is the central atom

A

The first atom listed, or the least electronegative

30
Q

What does it mean to be hypervalent

A

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

31
Q

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

A

Smallest

32
Q

What is the formula for formal charge

A

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

33
Q

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

A
  • 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
34
Q

What are delocalized electrons

A

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

35
Q

What is a resonance structure

A

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

36
Q

What does localized mean

A

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

37
Q

What is delocalized bonding

A

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

38
Q

Cyclic delocalization of bonding electrons may lead to _______ stability

A

Increased

39
Q

What are the three categories off octet rule expectations

A
  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
40
Q

What are radicals

A

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

CHEM110 (9 decks)

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