Ionic and Molecular Compounds Flashcards

1
Q

how do chemical bonds form?

A

when atoms lose gain or share valence electrons to acquire a close shell of valence electrons

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2
Q

ionic bonds

A

when valence electrons of a metal atom are transferred to the atom of a nonmetal and the resulting ions attract each other

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3
Q

covalent bonds

A

occur when nonmetal atoms share electrons to attain a noble gas arrangement

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4
Q

Na + ion

A

principle cation outside the cell: highest concentration outside the cell

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5
Q

K+ ion

A

principle cation inside teh cell

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6
Q

Ca2+ ion

A

cation found in bones

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7
Q

Mg2+ ion

A

cation found in bones

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8
Q

ionic compounds

A

consist of positive or negative charges held together by strong electrical attractions between oppositely charged ions

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9
Q

when do ionic compounds form

A

if the overall energy of the system decreases: we can obtain this through the born-haber cycle

allows us to understand if a compound will form spontaneously or not

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10
Q

the crystalline state

A

it is characterized by the arrangement of the ions in the 14 Bravais lattices

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11
Q

which transition metals cannot form 2 or more positive ions

A

Zn2+ , Cd2+ and Ag+

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12
Q

nomenclature used for metals with variable charge

A
  • the ion with the lower oxidation state gains the suffix -ous
  • the ion with the higher oxidation state gains the suffix -ic
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13
Q

which is the only polyatomic ion that does not have a negative charge

A

NH4 +

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14
Q

how are polyatomic ions derived?

A

from the loss of hydrogen ions by a molecule with an acid character

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15
Q

how to tell if a compound is ionic or covalent

A

ionic: if the first element in the formula is a metal or the ammonium ion
covalent: the first element in the formula is a nonmetal

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16
Q

describe how the covalent bond of a hydrogen molecules is formed

A

-forms as the atoms move closer and the positive charge of the nucleus attracts the electron of the other atom
-has a shared pair of electrons, a covalent bond, to give a noble gas arrangement of He to each H atom
- forms, when the molecule formed, is more stable than the 2 individual H atoms

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17
Q

which elements do not form octets

A

hydrogen and boron

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18
Q

which is the central atom in Lewis structure

A

the least electronegative

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19
Q

what is the importance of molecule structures?

A

molecules like drugs can be designed based on Lewis’s Theory eg thalidomide

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20
Q

why is the octet rule not right?

A
  1. hydrogen requires just 2e to form a noble gas arrangement
  2. nonmetals P, S, Cl, Br and I can form compounds with 10 or 12 valence electrons
  3. sulfur in SF6 are 12 valence electrons: 6 bonds
  4. in BCl3 the B atom has only 3 valence electrons to share.
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21
Q

electronegativity

A

ability to attract shared electrons by the nucleus

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22
Q

describe the changes of electronegativity along a period

A

increases from left to right: increasing the positive charge of the nucleus therefore stronger attraction for electrons

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23
Q

describe the changes of electronegativity down a group

A

increases from top to bottom as there is a decreasing distance of the valence electrons from the nucleus

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24
Q

why is the polarity of the bonds important

A

because polarity affects reactivity and solubility

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25
Q

what can be used to predict the polarity of a bond?

A

the difference in electronegativity of bonding atoms can be used

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26
Q

nonpolar covalent bond

A

occurs between nonmetals: it is an equal or almost equal sharing of electrons by the 2 bonding atoms and has a very small electronegativity difference between atoms

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27
Q

polar covalent bond

A

occurs between nonmetal atoms: it is an unequal sharing of electrons and has a moderate electronegativity difference

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28
Q

dipole

A

segregation of charges in a polar bond

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29
Q

electronegativity difference between 0 and 0.4

A

nonpolar covalent bond

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30
Q

electronegativity difference between 0.5 and 1.8

A

polar covalent bond

31
Q

electronegativity difference greater than 1.8

A

bond is ionic and the electrons are considered transferred

32
Q

polar molecules

A

one end of the molecule is more negatively charged than the other. the polar bonds in the molecule do not cancel each other out. the electrons are shared unequally in the polar covalent bond

33
Q

describe resonance structures

A

delocalised electrons: a single bond length is detected that is intermediate between single and double bonds.

34
Q

what does it mean when energy wise when several resonance forms can be drawn?

A

the actual energy of the molecule is lower than the energy of the individual structure because of higher entropy

35
Q

metallic bonding

A

lattice of metal ions bathed in a shared electron cloud

36
Q

alloys

A

the atoms of the added metals replace some positions in the array, leading to the same or different lattice with modulated properties

37
Q

perturbation theory

A

application of a quantum mechanics approximation

38
Q

what happens as 2 atoms approach each other?

A

it leads to an overlap between the orbitals: interaction between the nucleus of one atom and the electron of the other

39
Q

when do bonds form

A

when the interactions lead to a decrease in energy. the interaction is stabilised when 2 semi-occupied orbitals of similar sizes overlap

40
Q

when does the bond not form

A

when fully occupied orbitals overlap, the interaction leads to repulsion and the bond does not form

41
Q

hybridization

A

shuffling between differrent sublevel orbitals to give isoenergetic hybrid orbitals

it increases the electron probability density in a single lobe allowing better superposition with other orbitals; 4 hybrid isoenergetic sp3 orbitals are obtained

42
Q

why can carbon form 4 bonds

A

because 4 hybrid isoenergetic sp3 orbitals are obtained

43
Q

sp2 hybridisation

A

double bond
1s and 2p orbitals
3 sp2 orbitals
trigonal planar shape 120 degrees

type of bonds: 3 sigma + 1 pi

44
Q

sp hybridisation

A

triple bonds
1s and 1p orbital
2sp orbitals
linear shape 180 degrees

type of bond: 2 sigma + 2 pi

45
Q

sp3 hybridisation

A

single bonds
tetrahedral 109.5 degrees

types of bonds: 4 sigma

46
Q

pi bond

A

half filled py or pz orbital + half filled py or pz orbital

formed by the side-to-side overlap of p orbitals

47
Q

sigma bond

A

half fillled px orbital + half filled px orbital

head on overlap of atomic orbitals along the bond axis

48
Q

BF3

A

boron has an e configuration 1s2 2s2 2p1: sp2 hybridisation therefore 3 bonds and 1 unoccupied p orbital

49
Q

SF6

A

sulfur electron configuration: 1s2 2s2 2p6 3s2 3p4: it can form 6 sp3d2 hybrid orbitals

50
Q

VSEPR

A

electron groups are arranged as far apart as possible around the central atom to minimise charge repulsion

51
Q

dipole- dipole attractions

A

intermolecular force between 2 dipoles

52
Q

hydrogen bonds

A

strong dipole attractions when a hydrogen atom is bonded to F, O, or N

53
Q

van der waals

A

weak attractions between nonpolar molecules: caused by temporary dipoles that develop when molecules bump into each other

54
Q

intermolecular forces

A

forces between molecules

55
Q

intramolecular force

A

forces within a molecule

56
Q

list in increasing strength intermolecular and intramolecular bonds

A

dispersion forces
dipole-dipole attraction
hydrogen bond
covalent bond
ionic bond

57
Q

what affects the melting points of compounds

A

it is related to the strength of the attractive forces between molecules and compounds

58
Q

where is the melting point the highest

A

in ionic compounds due to the strong attractive forces between ions in the compound

59
Q

how are proteins stabilized

A

hydrogen bonds stabilise their structure

60
Q

how are nucleic acids stabilized

A

hydrogen bonds between complementary bases

61
Q

what stabilizes the conformation of macromolecules such as proteins and nucleic acids?

A

the sum of several weak forces: portions of the molecule that are several bonds get close to each other in space and attract weakly

62
Q

describe the structure of ethanol

A

ethanol has both a hydrophilic and a hydrophobic component.

63
Q

hand sanitisers

A

at 70% ethanol, the interactions between proteins and water are replaced by interactions with ethanol. these weak forces destabilize the structure of the structure of the proteins that lose their function

64
Q

what can ethanol disrupt?

A

hydrophobic interactions between nonpolar aa residues in proteins

65
Q

draw the molecular orbital diagram for when Zavg is less than 8

A

see notes

66
Q

draw the molecular orbital diagram for when Zavg is greater or equal to 8

A

see notes

67
Q

bond order

A

bond order = (electrons in bonding orbitals - electrons in antibonding orbitals)/ 2

68
Q

bonding molecular orbital

A

the sum of the wave function: a region where it is more likely to find an electron

69
Q

antibonding molecular orbital

A

subtraction of the wave function: does not favor the formation of a molecule

70
Q

paramagnetism

A

unpaired electrons: attracted to the magnetic field

71
Q

diamagnetism

A

paired electrons: repelled by a magnetic field

72
Q

bond order 1

A

single bond

73
Q

bond order 2

A

double bond

74
Q

why are antibonding orbitals at higher energy?

A

bc of the presence of nodal planes