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chemistry > 04 - chemical bonding > Flashcards

04 - chemical bonding Flashcards

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1
Q

what are cations?

A

a positively charged ion

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2
Q

what are anions?

A

a negatively charged ion

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3
Q

what is a lattice?

A

a regularly repeating arramgement of atoms, molecules or ions in three dimentions throughout the whole crystal structure

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4
Q

what are the van der Waals’ forces?

A
  • weak forces of attraction between molecules involving either id-id or pd-pd (+ hydrogen bonding)
  • a general term to describe all intermolecular forces (weak forces between molecules)
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5
Q

types of van der Waals’ forces?

A
  • instantaneous dipole-induced dipole (id-id) AKA. London dispersion forces
  • permanent dipole-permanent dipole (pd-pd)
  • hydrogen bond (a stronger form of pd-pd)
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6
Q

what are intermolecular forces?

A

the weak forces between molecules

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7
Q

Positive ion?

A

CATIONS
- loss of electrons
- usually metals
- to negative cathode

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8
Q

negative ion?

A

ANION
- gain of electrons
- usually non metal
- to positive anode

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9
Q

what is an ionic bond/electrocovalent bond?

A

the elctronstatic attraction between oppositely charged ion (cations and anions)

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10
Q

what are dot and cross diagrams?

A
  • a diagram showing the arrangement of the outer shell electrons in an ionic or covalent element or compound
  • electrons shown as dots or crosses to show their origin

shows:
. outer shell electrons in pairs
. charge of ion spread evenly
. square bracket
. ion charge art top right hand corner
. if more than two atoms types, uses circle, triangle, star, etc

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11
Q

what is a covalent bond?

A

the electrostatic attractions between the nuclei of two atoms and a shared pair of electron

represented by a single line between two atoms

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12
Q

what are lone pairs?

A

pairs of electrons in the outer shell of an atom that are not involved in bonding

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13
Q

what are the cases where covalently bonded compounds don’t have a noble gas configuration (electron octet)?

A

. BORON TRIFLURIDE (BF3) - electron deficient (6 electrons)

. SULFUR HEXAFLURIDE (SF6) - expanded octet (12 electrons)

. PHOSPHORUS (V) CHLORIDE (PCl5) - expanded octet (12 electrons)

. SULFUR DIOXIDE (SO2) - expanded octet (10 electrons)

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14
Q

what is a double covalent bond?

A

two shared pairs of electrons bonding two atoms together (two line)

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15
Q

what is triple covalent bond?

A

three shared pairs of electrons bonding two atoms together (3 lines)

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16
Q

what is a co-ordinate bond/ dative covalent bond?

A

the sharing of a pair of electrons between two atom where both electrons in the bond come from the same atom

need:
. one atom with lone pair of electrons
. a second atom to have an unfilled orbital to accept the lone pair (an electron deficient compound)

eg:
. NH4+
. Al2Cl6

diplayed by arrow pointing away from lone pair

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17
Q

what is bond energy?

A

the energy required to break one mole of a particular covalent bond in the gaseous state

used to measure the strength of a bond

units = kJ mol-1

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18
Q

what is bond length?

A

. the distance vetween the nuclei of two covalently bonded atoms

. more bond strength = less reactive

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19
Q

why are double bonds shorter and have more energy than single bonds?

A

. more quantity of nuclear charge between two atomic nuclei

. more force

. more attraction

. more bond strength

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20
Q

factors affecting the reactivity of a molecule?

A

. bond polarity
. bond strength
. whether bond is sigma or pi

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21
Q

what does VESPR stand for?

A

Valence Shell Electron Pair Repulsion theory

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22
Q

what does VESPR stand for?

A

Valence Shell Electron Pair Repulsion theory

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23
Q

what does the VESPR theory state?

A

. valence shell electrons are the elctrons in the main outer shell

. electron pairs repel each other since they have the same charge

. lone pairs repel more than bond pairs

. double bond repulsion > multiple single or single bond repulsion

. shape of a molecule can be deduced using this theory

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24
Q

what is the order of repulsion between pairs?

A

lone-lone > lone-bond >bond-bond

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25
Q

why do lone pairs repel more than bond pairs?

A

lone pairs have more concentrated electron charge clouds, and they are both wider and closer to the nucleus

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26
Q

what is the shape and angle of methane?

A

tetrahedral, 109.5°

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27
Q

what is the shape and angle of ammonia?

A

pyramidal, 107°

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28
Q

what is the shape and angle of water?

A

nonlinear V shape, 104.5°

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29
Q

what is the shape and angle of boron trifluoride?

A

trigonal planar, 120°

30
Q

what is the shape and angle of carbon dioxide?

A

linear, 180°

31
Q

what is the shape and angle of phosphorus pentafluoride?

A

trigonal bipyramidal, 120° and 90°

32
Q

what is the shape and angle of sulfur hexafluoride?

A

octahedral, 90°

33
Q

what is molecular orbital?

A

combined orbital formed from the overlap of atomic orbitals ina covalent bond, contains 2 atoms

greater the overlap, stronger the bond

34
Q

what is hybridisation?

A

the mixing of atomic orbitals

35
Q

hybridiasation: what s and what p make what?

A

. s + one p = sp hybrid orbitals
. s + two p = sp² hybrid orbitals
. s + three p = sp³ hybrid orbitals

36
Q

per atom, number of lone pair + number of sigma bonds

A

2 - sp
3 - sp²
4 - sp³

37
Q

what is a sigma bond?

A

head on overlapping of orbitals, electrons delocalised, forms stronger bonds

38
Q

whta are pi bonds?

A

lateral overlapping of orbitals, electrons more delocalised, forms relatively weaker bonds

39
Q

how many sigma and pi bonds in a SINGLE bond?

A

1 sigma

40
Q

how many sigma and pi bonds in a DOUBLE bond?

A

1 sigma bond, 1 pi bond

41
Q

how many sigma and pi bonds in a TRIPLE bond?

A

1 sigma, 2 pi

42
Q

what is metallic bonding?

A

the electrostatic sttraction between positive ions and delocalised electrons, STRONG, atoms packed in a lattice

43
Q

what are delocalised electrons?

A

electrons that are not assiciated with any particular atom - IN METALS they move throughout the metallic structure between the metal ions when a voltage is applied

44
Q

what is a lattice?

A

a regular arrangement where atoms are packed closely together

45
Q

more metallic bonding…

A

. more positive charge on ions in the metallic lattice
. less size of metal ions in the lattice
. more number kf mobile electrons per atoms

46
Q

what are the properties of metals?

A

. high melting and boiling points
. strong attractions between ions and electrons
. conduct electricity
. conduct heat

47
Q

what is electronegativity?

A

the power/tendency of a particular atom that is covalently bonded to another atom to attract the bonding pair of electoens towards itself

48
Q

across a period, electronegativity…

A

increases

49
Q

up a group, electronegativity…

A

increases

50
Q

most electronegative element?

A

fluorine

51
Q

least electronegative element?

A

caesium

52
Q

what factors influence electronegativity?

A

. NUCLEAR CHARGE - same period with more nuclear charge, more electronegativity

. ATOMIC RADIUS - same group atoms with more outer electron distance from nucleus, less electronegativity

. SHIELDING - more inner electron shells and sub shells, less electronegativity

53
Q

oxygen electronegativity value?

A

3.5

54
Q

carbon electronegativity value?

A

2.5

55
Q

what is the Pauling electronegativity scale?

A

a commonly used scale of electronegativity values

symbol = Np
units = none

56
Q

high electronegativity value difference = ?

A

ionic compound

57
Q

low electronegativity value difference = ?

A

covalent bond

58
Q

what does non polar mean?

A

when the electronegativity values of the two atoms forming a covalent bonds are the same (eg H2, Cl2, Br2)

59
Q

what happens in a non polar molecule?

A

when a covalent bond is formed between two atoms having different electronegativity values

MORE ELECTRONEGATIVE ATOM ATTRACTS THE BOND PAIR TOWARDS IT

thus:
. centre of positive charge doesn’t coincide witht he negative charge
. asymmetric electron distribution
. both atoms partially charged

. less electronegative has delta positive sign
. more electronegative have delta negative sign

. say that bond is polar/has a dipole

60
Q

what is dipole moment?

A

the product of the magnitude of the charge and the distance between the centres of the positive and negative charges

used to measure the degree of polarity of a molecule

shown with arrow, head pointing to partially negative end

61
Q

can determine charge distribution by

A

X ray spectroscopy

62
Q

more polar =? reactive

A

more reactive

63
Q

id-id

A

instantaneous dipole - induced dipole forces

. weakest intermolecular attractive force
. results from temporary id id forces in both polar and non polar molecules

64
Q

more id id :

A

. more electrons
. more number of contact point
. more boiling point
. more strength

65
Q

what are pd-pd forces?

A

permanent dipole - permanent dipole

attractive intermolecular forces which result from permanent dipoles in molecules

. molecules with a permanent dipole are called POLAR MOLECULES
. often stronger than id id
. often higher boiling point than id id

66
Q

what is hydrogen bonding

A

. strong type of pd pd force
. the strongest form of intermolecular bonding
. weaker than covalent bond

67
Q

what is the requirements for hydrogen bonding to occur?

A

. H atom covalently bonded to highly electronegative (eg N, F, O)
. another highly electronegative with a lone pair of electrons

68
Q

properties of water?

A

. more boiling point (more hydrogen bonding)

. more enthalpy change of vaporisation (more hydrogen bonding)

. high surface tension (hydrogen bonds exert a significant downward force at the liquid surface)

. more viscosity (hydrogen bonding reduces ability of water molecules to side over each other)

. more dense than ice (rigid lattice with each O atom surrounded by H atoms, long bond lengths, more apart than in liquid)

69
Q

IONIC COMPOUNDS?

A

. solid at rtp
. high mp, bp, high enthalpy changes vaporisation
. soluble in water
. don’t conduct when in solid state

70
Q

METAL PROPERTIES?

A

. solids (not mercury)
. high mp, bp, high enthalpy changes vaporisation
. insoluble in water
. conduct in solid and molten

71
Q

COVALENT COMPOUNDS PROPERTIES?

A

. solid, liquid, gas
. some insoluble, some soluble
. some react not dissolve
. don’t conduct electricity

chemistry (18 decks)

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