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Chemistry > 2.2 > Flashcards

2.2 Flashcards

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1
Q

what is a discrete molecule

A

an electrically neutral group of two or more atoms held together by chemical bonds

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2
Q

state some exceptions to the octet rule

A

beryllium chloride
boron trichloride
phosphorus(V) chloride
sulfur hexafluoride

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3
Q

what is a displayed formula

A

shows each bonding pair as a line drawn between the atoms involved (H-O-H)

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4
Q

what is a dative bond

A

a dative bond is formed when an empty orbital from one atom overlaps with an orbital containing a lone pair of electrons of another atom

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5
Q

what is the electron pair repulsion theory

A

the shape of a molecule or ion is caused by repulsion between bonding pairs and lone pairs of electrons that surround the central atom
the electron pair arrange themselves around the central atom so that the repulsion between them is a minimum

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6
Q

what shape is a molecule with 2 bond pairs and its bond angle

A

linear
180

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7
Q

what shape is a molecule with 3 bond pairs and its bond angle

A

trigonal planar
120

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8
Q

what shape is a molecule with 4 bond pairs and its bond angle

A

tetrahedral
109.5

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9
Q

what shape is a molecule with 5 bond pairs and its bond angles

A

trigonal bipyramidal
90 and 120

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10
Q

what shape is a molecule with 6 bond pairs and its bond angle

A

octahedral
90

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11
Q

what shape is a molecule with 3 bond pairs and 1 lone pair and its bond angle

A

trigonal pyramidal
107

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12
Q

what shape is a molecule with 2 bond pairs and 2 lone pairs and its bond angle

A

V-shaped
104.5

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13
Q

define dipole

A

exists when two charges of equal magnitude but opposite signs are separated by a small distance

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14
Q

what is a dipole caused by

A

the more electronegative element attracts the electrons resulting in separation of charge

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15
Q

what molecule shapes are symmetrical (therefor dipoles cancel out)

A

linear
trigonal planar
tetrahedral (some exceptions such as CHCl3)

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16
Q

explain london forces

A

electron density fluctuates over time in a molecule
at any instant the electron density can become unsymmetrical generating an instantaneous dipole
which then induces a dipole in a neighboring molecule
these dipoles then attract one another

17
Q

state 3 features of london forces

A

attractive force increases with increasing number of electrons in a molecule
the strength of these attractions depends upon the shape and size of the molecules (the more points of contact between molecules the greater the london forces)
they’re always present with any molecules

18
Q

explain permanent dipoles

A

if 2 permanent dipoles are aligned correctly they will attract one another

19
Q

are london forces or permanent dipoles stronger and why

A

london forces are stronger because in order for permanent dipoles to occur the molecules must be correctly aligned

20
Q

define hydrogen bond

A

an intermolecular interaction between a hydrogen atom of a molecule bonded to an atom which is more electronegative than hydrogen and another atom in the same or a different molecule

21
Q

what are the 3 most common atoms hydrogen bonds form with

A

oxygen
nitrogen
fluorine

22
Q

what is the rough bond angle of hydrogen bonds

A

180

23
Q

how do hydrogen bonds form between water molecules

A

partial bond formation occurs between the lone pairs from an oxygen and a hydrogen atoms of another water molecule

24
Q

what groups can form hydrogen bonds

A

amines
alcohols

25
Q

what is the only significant interaction between alkane molecules

A

london forces

26
Q

why does boiling temperature increase as relative molecular mass (chain length) of alkanes increases

A

number of electrons per molecule increases so london forces are increased
number of points of contact increases so london forces increase

27
Q

how does branching of alkanes effect boiling temperature and why

A

lowers boiling temperature as there are fewer points of contact for london forces

28
Q

why do alcohols have higher boiling temperatures than alkanes

A

because alcohols have an OH group and can therefor form hydrogen bonds on top of london forces which require more energy to overcome than just london forces

29
Q

why does boiling temperature increase from HCl -> HBr -> HI

A

due to increased number of electrons per molecule so there is an increase in london forces

30
Q

why does water have a relatively high mp & bp

A

water has hydrogen bonds which have strong intermolecular forces of attraction that require a lot of energy to overcome

31
Q

why does HF have a lower boiling point than water even though they have the same number of electrons

A
  • both form the same london forces (roughly)
  • both form hydrogen bonds
    however
    HF on average only forms on hydrogen bond per molecule whereas water forms 2
    not all of the hydrogen bonds are broken in the vaporization of HF whereas they are in water
32
Q

why is ice less dense than water

A

ice is arranged in rings of 6 held by hydrogen bonds creating large areas of space inside the rings so when ice melts the ring structure is destroyed and distance between molecules decreases

33
Q

how do solutes dissolve in solvents

A

the solute particles must particles must separate from each other and become surrounded by solvent particles
the force of attraction between solute and solvent must be strong enough to overcome solute-solute attractions and solvent-solvent attractions

34
Q

where does the energy come from when dissolving ionic solids

A

hydration of ions

35
Q

explain the hydration of an ionic solid

A

the dipole negative attracts the anions sufficiently to remove them from the lattice and the anion becomes surrounded by water molecules
the dipole positive attracts the cations and surrounds the cation in water molecules

36
Q

how is solubility of alcohols effected by chain length

A

solubility decreases as chain length increases as london forces predominate between the alcohol molecules

37
Q

why may a substance not dissolve in water

A

it is a non-polar molecule therefor can’t form hydrogen bonds with water molecules
attractions between the molecule and water is not strong enough to disrupt the hydrogen bond system

Chemistry (46 decks)

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