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Georges chem > shapes of molecules and intermolecular forces chp 6 > Flashcards

shapes of molecules and intermolecular forces chp 6 Flashcards

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1
Q

what is electron-pair repulsion theory used for

A

The electron-pair repulsion theory is a model used in chemistry for explaining and predicting the shapes of molecules and polyatomic ions

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2
Q

what are the main ideas behind electron-pair repulsion theory

A
  • number of electron pairs arround central atom determine shape of molecule
  • electron pairs repel eachother as far away as possible
  • static shape of molecule is where repulsion between pairs is minimised
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3
Q

when drawing a molecule is 3D what does a solid line represent

A

represents a bond in the plane of the paper

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4
Q

when drawing a molecule in 3D what does a dotted wedge represent

A

represents a bond going into the plane of the paper

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5
Q

When drawing a molecule in 3D what does a solid wedge represent

A

it represents a bond coming out of the plane of the paper

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6
Q

why do lone pairs have a stronger repulsive force than bonded pairs

A

A lone pair of electrons is slightly closer to the central atom, and occupies more space than a bonded pair. This results in lone pairs repelling more strongly.

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7
Q

what is the trend in repulsion between pairs of different kinds

A
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8
Q

what is the shapes table

A

bonded pairs on left, lone pairs on right side

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9
Q

what actually is the bond angle

A

the angle between the bonded pair of electrons

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10
Q

what are some examples of ions with a trigonal planar strcuture

A
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11
Q

what is an example of an ion that has a tetrahedral structure

A
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12
Q

what is electronegativity

A

electronegativity is a measure of an atoms ability to attract electron towards it in a covalent bond

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13
Q

on what scale is the electronegativity measured

A

the pauling scale

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14
Q

what is the trend in electronegativity across the periodic table

A

increases up and across the peridoic table

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15
Q

if the pauling value is high does that mean the element is highly electronegative or barly electronegative

A

it means its highly electronegative

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16
Q

what are the most electronegative elements

A
  • nitrogen
  • oxygen
  • fluroine
  • chlorine
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17
Q

what are the least electronegative elements

A
  • group 1 metals
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18
Q

what differences do there need to be in the pauling value of atoms for different types of bonding to occur

A
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19
Q

how are electrons shared in a non-polar bond

A

in a non-polar, the bonded electron pair is shared equally between the bonded atoms

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20
Q

when will a bond be non-polar

A

-if the bonded atoms are the same
-the bonded atoms have the same or similar electronegativity

21
Q

what is a pure covalent bond

A

a covalent bond that forms between two atoms of the same element and so the electrons are shared between the atoms equally.

22
Q

what is a polar bond

A
  • bonded electron pair is shared unequally between bonded atoms
  • polar when pauling values differing by 0.4
23
Q

what is a dipole

A
  • a charge separation due to uneven electron sharing in a covalent bond,
24
Q

what are the characteristics of a dipole on a non-polar molecule

A
  • a dipole on a non-polar molecule will be an induced dipole brought about my nucleo/electrophiles
25
Q

how can multiple permenant dipoles within a molecule effect the overall features of the molecule

A
  • if acting in opposite directions can cancel out
  • may reinforce one another producing larger dipole
26
Q

what are intermolecular forces

A
  • weak interactions between dipoles of different molecules
27
Q

what are the 3 main categories of intermolecular forces

A
  • induced dipole-dipole intertactions (london forces)
  • permanent dipole-dipole interactions
  • hydrogen bonding
28
Q

what are characteristics that intermolecular forces are largely responsible for

A

responsible for physical properties such as melting and boiling points, whereas covalent bonds determine the identity and chemical reactions of molecules

29
Q

what is the trend in intermolecular force strength within the 3 main categories

A
30
Q

what are london forces

A

London forces are weak intermolecular forces that exist between all molecules, wether polar or non-polar, They act between induced dipoles in different molecules.

31
Q

How are induced dipoles formed

A

-movement of electrons produces a changing dipole in a molecule
-at any instant, an instantaneous dipole will exist, but its position is constantly shifting
-The instantaneous dipole induces a dipole on a neighbouring molecule
-The induced dipole induces further dipoles on neighbouring molecules, which then attract one another

32
Q

what determines the strength of an induced dipole

A

the number of electrons in the molecule

33
Q

what do more electrons in a molecule mean for the induced dipole

A

the more the electrons in each molecule:
-the larger the instantaneous and induced dipoles
-the greater the induced dipole-dipole interactions
-the stronger the attractive forces between molecules

34
Q

How does the number of electrons and therefore the characteristics of the induced dipole within a molecules affect the boiling point of the molecule

A

-larger numbers of electrons mean larger induced dipoles
-more energy is then needed to overcome the intermolecular forces, increasing the boiling point

35
Q

what is a simple molecular substance

A

A simple molecular substance is made up of simple molecules (small units containing a definite number of atoms with a definite formula).

36
Q

what is the structure of simple molecular substances when in a solid state

A

simple molecules form a regular structure called a simple molecular lattice

37
Q

what are the features of a simple molecular covlanet lattice

A

low melting and boling point with varying solubility depending on the polarity

38
Q

what explains the low melting and boiling point in a simple molecular substance

A
  • Intermolecular forces: Weak forces (van der Waals, dipole-dipole, hydrogen bonding) between molecules
  • Molecular size: Smaller molecules experience weaker london forces
  • Polarity: Nonpolar molecules have lower melting and boiling points compared to polar molecules due to weaker intermolecular forces.
39
Q

what occurs when a simple molecular substance is melted

A

only the weak intermolecular forces break, the covalent bonds are strong and do not break

40
Q

what is the solubility of non-polar simple molecular substances in non-polar solvents

A
  • compounds are soluble
  • interactions between solvent and compound which causes compound to dissolve
41
Q

what is the solubility of non-polar simple molecular substances in polar solvents

A
  • they are insoluble
    ^intermolecular bonding within polar solvent is too strong to be broken
    ^little interaction between substances
42
Q

what is the solubility of polar simple molecular substances

A

-Polar covalent substances may dissolve in polar solvents as the polar solute molecules and the polar solvent molecules can attract each other(process is similar to dissolving ionic compounds).

43
Q

what determins the solubility of polar simple molecular substances

A

the solubility depends on the strength of the dipole of each atom of each element within the polar simple molecular substances.

44
Q

Can a substances dissolve in both polar and non-polar solvents

A

compounds containing both polar and non-polar parts in their structure such as ethanol can dissolve in both polar and non-polar solvents

45
Q

Are simple molecular compounds electrically conductive

A
  • no charge carriers so no matter if solid, molten or aqeous will not conduct electricity

covalent bonding

46
Q

what is a Hydrogen bond

A

a hydrogen bond is a special type of permanent dipole-dipole interaction found between molecules containing:

-an electronegative atom with a lone pair of electrons
-a hydrogen atom attached to an electronegative atom

47
Q

Are hydrogen bonds strong or weak

A

strong, they are the strongest type of intermolecular attractions

48
Q

How does hydrogen bonding affect the density of solid water

A
  • Hydrogen bonds hold water molecules apart in an open lattice structure
  • the water molecules in ice are further apart than in water
  • solid ice is less dense than liquid water floats
49
Q

How does hydrogen bonding affect the melting and boiling points of water

A
  • it increases the boiling/melting point
    ^high quantity energy needed to melt/boil water than if just had london forces

Georges chem (29 decks)

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