Chapter 10: Molecular Structure and Bonding Theories Flashcards Preview

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Flashcards in Chapter 10: Molecular Structure and Bonding Theories Deck (83):
1

the arrangement of the atoms in a molecule has a strong influence on its

physical properties and chemical reactivity

2

the valence-shell electron-pair repulsion (VSEPR) model predicts the shapes of most molecules from their

Lewis structures

3

the main premise of VSEPR model is that the electron pairs about an atom

repel each other

4

VSEPR Rule 1: a molecule hs a shape that .....

minimizes eletrostatic repulsions between valence-shell electron pairs

5

minimum repulsion results when the electron pairs are as

far apart as possible

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the VSEPR model predicts the shape around

each central atom

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steric number =

(number of lone pairs on central atom) + (number of atoms bonded to central atom)

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the steric number is used to determine the

bonded-atom lone-pair arrangement

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the BALPA is the shame that maximizes the distances between

regions of electron density about a central atom

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bond angles for linear

180

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bond angles for trigonal planar

120

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bond angles for tetrahedral

109.5

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bond angles for trigonal bipyramidal

90 and 120

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bond angles for octahedral

90 and 90

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SN: 2, balpa:

linear

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SN: 3, BALPA:

trigonal planar

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SN: 4, BALPA:

tetrahedral

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SN: 5, BALPA:

trigonal bipyramidal

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SN: 6, BALPA:

octahedral

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two positions for molecular shapes:

axial and equatorial

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axial atoms have different ... from equatorial ones

environments

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when central atoms have lone pairs, the molecular shape is not the same as the

bonded-atom lone-pair arrangement

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the molecular shape is the geometric

arrangement of the atoms in a species

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the lone pairs influence the molecular shape but are ..., because there are no atoms at the ...

not part of it; locations of the lone pairs

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each type of electron pair exerts a different

repulsion on other electron pairs

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VSEPR Rule 2: forces between electron pairs vary as

lone-pair-lone-pair repulsion>lone-pair-bonding-pair repulsion>bonding-pair-bonding-pair repulsion

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in a trigonal bipyramidal BALPA, the structure that minimizes the number of 90 degree lone pair interactions is favored-

lone pairs always go to the equatorial position

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for molecules with more than one central atom, the geometry about each atom is assigned by applying the VSEPR model to each

central atom individually

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the VSEPR model does not predict how the geometry around one central atom will be oriented with respect to

others in the moleule

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polar molecules will orient to maximie

electrostatic attractions

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the degree of polarity is measured by a

dipole moment

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the dipole moment is the magnitude of the separated charges times the

distance between them

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the ... between bonded atoms is used to predict the polarity of each bond, known as the ...

difference in electronegativity; bond dipole

34

the dipole moment of the molecule is the

vector sum of the individual bond dipoles

35

molecules with lone pairs of electrons on a central atom generally are

polar

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a molecule with polar bonds is nonpolar if its geometry causes the

bond polarities to sum to zero

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molecules are nonpolar when there are no ... on the central atom and all of the atoms bonded to the central atom are ...

lone pairs; identical

38

valence bond theory describes covalent bonds as being fromed by atoms sharing valence electrons in

overlapping valence orbitals

39

(valence bond theory) the bonding is based on the ... available to make bonds and the .... that the atoms provide for bonding

orbitals; number of valence electrons

40

hybrid orbitals are orbitals obtained by

mixing two or more atomic orbitals of the same central atom

41

the new hybrid orbitals have different ... and ... properties from the orbitals used in constructing them

shapes; directional

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the energy and directional characteristics of the new hybrid orbitals are decided by the ... and ... of atomic orbitals used in the mixing

type; number

43

1 s orbital + 1 p orbital forms

two sp hybrid orbitals

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the sp hybrid orbitals describe the bonding on central atoms that have

180 degree bond angles

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the steric number of 2 indicates ... hybrid orbitals

sp

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1 s orbital + 2 p orbitals forms

3 sp^2 hybrid orbitals

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for sp2 hybrid orbitals, ... remains unchanged

one p orbital

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the sp2 hybrid orbitals describe the bonding on atoms that have ... and a steric number of ..

120 degree bond angles; 3

49

1 s orbital + 3 porbitals forms

4 sp^3 hybrid orbitals

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the sp3 hybrid orbitals describe the bonding on central atoms that have approximately .... and a steric number of ..

109-degree bond angles; 4

51

for molecules that have central atoms with steric numbers of 5 or 6, more than ... are needed to make the hybrid orbitals

four atomic orbitals

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the additional orbitals are taken from the

d subshell

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1 d orbital + 1 s orbital + 3 p orbitals forms

5 sp^3d hybrid orbitals

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2 d orbitals + 1s orbital + 3 p orbitals

six sp^3d^2 hybrid orbitals

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the steric number and number of hybrid orbitals are

equivalent

56

sigma bonds exist int he region

directly between two bonded atoms

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in a sigma bond, the shared pair of electrons is symmetric about th eline

joining the two nuclei of the bonded atoms

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all single bonds are

sigma bonds

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sigma bonds form from the overlap of ... orbitals or hybrid orbitals oriented ...

s or p; along the bond

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all hybrid orbitals make only

sigma bonds

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pi bonds exist in the region ... between two bonded atoms

above and below a line drawn

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double bonds have .. sigma bond and ... pi bond

1; 1

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triple bonds have .. sigma bond and ... pi bond

1; 2

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isomers are compounds with the same ... but different ...

molecular formula; structures

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when double bonds are formed between two carbon atoms, the potential for ... isomerism arises due to lack of ... around double bonds

cis-trans; rotation

66

cis-trans isomerism is observed only if each carbon atom has

2 different substitutents attached

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pi bonds contribute to the ... model of electrons in bonding, and help explain ..

delocalized; resonance

68

electron density from pi bonds can be distributed ... all around the ring, above and below the plane

symmetrically

69

molecular orbital theory is a model that combines atomic orbitals to form new orbitals that are shared over the

entire molecule rather than between two atoms

70

a molecular orbital is a ... of an electron in a molecule

wave function

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the number of molecular orbitals formed must equal the number of

atomic orbitals used to make them

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these wave functions can be added to generate ... or they can be subtracted to generate ...

bonding orbitals; anti-bonding orbitals

73

bonding orbitals concentrate electron density

between atoms

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anti-bonding orbitals reduce the

electron density between atoms

75

bonding molecular orbitals are ... and antibonding molecular orbitals are ... than the atomic orbitals that are combined

more stable; less stable

76

moleuclar orbital theory allows us to calculate bond order (...) and the number of unpaired electrons (...)

measure of stability; paramagnetism

77

according to molecular orbital theory, bond order is :

1/2(# e- in bonding orbitals - #e- in anti-bonding orbitals)

78

a homonuclear diatomic molecule contains

two atoms of the same element

79

heteronuclear diatomic molecules contain one atom of each of

two different elements t

80

the molecular orbital diagrams are close to those for homonuclear diatomic molecules when the valence energies for each atom are

fairly close in energy

81

delocalized molecular orbitals are: orbitals in which an electron in a molecule is

spread over more than two atoms

82

cis: same substituents

parallel

83

trans: substitutents are

opposite to each other