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LC Chemistry > shapes and forces > Flashcards

shapes and forces Flashcards

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1
Q

intermolecular forces

A

attractive (repulsive) forces between molecules

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2
Q

intramolecular forces

A

attractive (repulsive) forces within a molecule

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3
Q

Van der Waals forces

A

weak attractive forces between molecules resulting from the formation of temporary dipoles

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4
Q

Dipole-Dipole

A

Dipole-Dipole forces are forces of attraction between the negative pole of one molecule and the positive pole of another

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5
Q

hydrogen bonds

A
  • particular types of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine
  • the hydrogen atom carries a partial positive charge and is attracted to the electronegative atom in another molecule. Thus, H acts as a bridge between two electronegative atoms
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6
Q

the Law of Conservation of Mass

A

the total mass of the products of a chemical reaction is the same as the total mass of the reactants

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7
Q

the Law of Conservation of Matter

A

that in any chemical reaction, matter is neither created nor destroyed but merely changes from one form into another

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8
Q

types of shapes

A 
linear
v-shaped
trigonal planar
trigonal pyramidal
tetrahedral
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9
Q

only bonding pairs around the central atom

A

electrons in the bonding pairs repel each other and want to be as far apart as possible

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10
Q

no. of bonding pairs around central atom - 2

A

shape of molecule - lienar

example - BeH₂ , BeCl₂

bond angle - 180°

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11
Q

no. of bonding pairs around central atom - 3

A

shape of molecule - trigonal planar

example - BF₃ BCl₃

bond angle - 120°

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12
Q

no. of bonding pairs around central atom - 4

A

shape of molecule - tetrahedral

example - CH₄

bond angle - 109.5°

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13
Q

lone pairs and bonding pairs around central atom examples

A

in hback

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14
Q

shapes of molecules

A
  • molecules formed when atoms are joined together by covalent bonds
  • arrangement of atoms dictates shape of molecule
  • figure out arrangement using Electron Pair Repulsion Theory
  • Look at the bonding pairs or lone pairs around central atoms
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15
Q

lone pairs and bonding pairs around central atom

A
  • lone pairs of electrons closer to nucleus of atom (nuclear charge sucks them in)
  • bc of this they are closer together (create strong negative charge)
  • their collective nuclear charge pushes bonding pairs further apart
  • decreases the bond angle + distorts shape of molecule
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16
Q

polarity

A
  • atoms in covalent bonds share electrons

- we figure it out by looking at electronegativity

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17
Q

non-polar

A

when atoms in a covalent bond share electrons equally, bond is said to be non-polar

Eg. H₂ , N₂ , O₂

18
Q

polar

A

when electrons are shared unequally, bond is polar

eg. HCl, NH₄

19
Q

electronegativity

A
  • the greater the electronegativity, greater the pull on electrons
  • to work it out use electronegativity table
  • atom w/ greater pull on electrons becomes slightly negative while other atom in bond becomes slightly positive
20
Q

use of electronegativity

A

can be used to predict nature of a bond

21
Q

everyday life: polar

A

water (good solvent for ionic and polar substances)

ethanol (used in alcoholic beverages)

22
Q

everyday life: non-polar

A

tetrachloroethene (used in dry cleaning)

propanone (also called acetone) (used in nail varnish remover)

23
Q

polar molecule can be non-polar overall if it has these shapes

A

linear
trigonal planar
tetrahedral

ie shapes with no lone pairs

24
Q

eg of polar molecules that is non-polar overall

A

BeH₂
BF₃
CH₄

25
Q

molecules that are not symmetrical (has one lone pair) are one of these shapes

A

trigonal pyramidal

v-shaped

26
Q

eg of non-symmetrical molecules

A

NH₃

H₂

27
Q

polar bonds and shapes

A

some molecules, even tho they have polar bonds, doesn’t mean they are polar molecules due to their shapes

(shape is symmetrical as there are no lone pairs of electrons)

eg. carbon dioxide, chloroform, boron trichloride

28
Q

intermolecular bonding

A

between molecules

eg. between water molecules

29
Q

intramolecular bonding

A

within the molecule

eg. an oxygen atom and a hydrogen atom in a molecule

30
Q

3 types of intermolecular bonding

A

Van der Waals
Dipole-Dipole
Hydrogen Bonding

31
Q

intermolecular bonding: Van der Waals forces

A
  • temporary dipoles can be set up in non-polar molecules (eg. H₂, O₂)
  • weak forces of attractions can be set up between oppositely charged poles in the atom
  • do not last v long
  • weakest of 3 types
  • low boiling points
32
Q

intermolecular bonding: Dipole-DIpole forces

A
  • polar molecules have positive + negative poles eg. HCl
  • positive pole of one molecule can become attracted to negative pole of another
  • much weaker than ionic bonds
33
Q

intermolecular bonding: Hydrogen Bonding

A
  • strongest of 3
  • N, O, and F are v. electronegative (when bonded with hydrogen, the electron spends more time on the N, O, or F –> creates strong poles)
  • High boiling points
34
Q

exception to octet rule

A

BF₃ (boron trifluoride)

has trigonal planar shape
does not satisfy octet rule (no lone pair present to make 8 in outer shell) as the 3 covalent bonds are stable enough

35
Q

electron pair repulsion theory

A

The shape of a molecule or ion is governed by the arrangement of the electron pairs around the central atom.

to do with repulsion between bond pairs and (if any) lone pairs

36
Q

why h2o has v planar shape

A

repulsion between two bond pairs and two lone pairs

37
Q

intermolecular vs intramolecular bonds (not definitions)

A

intramolecular: forces which keeps molecule together, ie. bonds
intermolecular: attractive forces between molecules. Responsible for keeping matter in solid or liquid phase

38
Q

bond angles

A

know the bond angles

39
Q

Predict the type of bond formed between carbon and chlorine atoms in CCl4

A

polar covalent

40
Q

“why does x have a lower bp than y?”

A

If electroneg diff is lower in x, then say “smaller degree of intermolecular forces”

LC Chemistry (26 decks)

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