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Chemistry > 4. Chemical Bonding & Structure > Flashcards

4. Chemical Bonding & Structure Flashcards

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1
Q

Are metals cations or anions?

A

Cations

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2
Q

Describe the four properties of ionic compounds.

A
  • High melting point- lots of energy required to break strong electrostatic forces.
  • Crystalline- ions have a regular arrangement in their lattice.
  • Conduct electricity when molten or solid- ions are free to move.
  • Brittle- small displacement of lattice causes like ions to align and repel.
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3
Q

Define ‘ionic bond’.

A

The electrostatic force of attraction between oppositely charged ions.

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4
Q

What type of ions will have the greatest force of electrostatic attraction?

A

Small ions with a large charge.

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5
Q

Define ‘metallic bond’.

A

Positive metal cations are attracted to delocalised electrons by strong electrostatic forces.

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6
Q

What is the structure of a metallic structure?

A

Giant 3D crystal lattice

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7
Q

Describe the four properties of metallic bonds.

A
  • High melting point- cations are held to electrons by strong electrostatic forces.
  • Malleable and ductile- ions are glued into new positions by delocalised electrons.
  • Conduct electricity- delocalised electrons are free to move in a given direction.
  • Conductor of heat- ions are closely packed, so vibrations transfer easily.
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8
Q

Define ‘covalent bond’.

A

A pair of shared electrons.

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9
Q

What is a co-ordinate bond?

A
  • A type of bond formed when both electrons come from the same atom.
  • The lone pair of electrons help to fill the other atom’s outer shell.
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10
Q

How is a co-ordinate bond represented?

A

—>

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11
Q

What is the electronegativity difference for a polar bond?

A

At least 0.5

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12
Q

What are the three types of intermolecular force?

A
  • London dispersion forces
  • Dipole-dipole forces.
  • Hydrogen bonding.
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13
Q

Describe the features of London dispersion forces.

A
  • Present between all molecules and atoms.
  • Instantaneous dipole forms
  • Very weak
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14
Q

Describe how an instantaneous dipole forms.

A

The electrons are constantly moving, causing one side of the molecule to be slightly charged. This causes the other molecule to be instantaneously attracted.

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15
Q

Describe the features of dipole-dipole forces.

A
  • Some unsymmetrical molecules have permanent dipoles.
  • The permanently negative end of one molecule is attracted to the permanently positive end of the other molecule.
  • Approximately 1% the strength of a covalent bond.
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16
Q

Describe the features of hydrogen bonding.

A
  • A type of permanent dipoles due to permanent dipole force.
  • About 10% strength of a covalent bond.
  • H must be bonded to N, O or F.
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17
Q

Describe the features of a giant molecular structure.

A
  • High melting point- many covalent bonds needed to break.
  • Don’t conduct electricity (except graphite)- no free ions/ electrons.
  • Hard- exists in a tetrahedral structure.
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18
Q

Describe the features of diamond

A
  • Very high melting point- covalent bonds must be broken.
  • Very strong- each carbon is joined to 4 other carbons.
  • Doesn’t conduct electricity- no free electrons.
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19
Q

Describe the features of graphite.

A
  • Very high melting point.
  • Soft- layers are held by weak London forces which can slide over each other.
  • Can conduct electricity- delocalised electron as only 3 carbon bonds used.
20
Q

Describe the features of silica.

A
  • Very high melting point.
  • Strong
  • Each silicon atom is joined to four oxygens.
  • Each oxygen is bonded to 2 silicons
  • Doesn’t conduct electricity.
21
Q

What are resonance structures?

A

Sets of Lewis structures that describe the delocalisation of electrons in a polyatomic ion or molecule.

22
Q

What are delocalised electrons?

A

Electrons in a molecule, ion or solid metal that are not associated with a single atom or one covalent bond.

23
Q

What must a molecule have to be able to exhibit a resonance hybrid?

A

A pi bond that can move from one part of the molecule to another.

24
Q

Why are oxygen and ozone dissociated by different wavelengths of light?

A
  • The chemical bonds between the oxygen in ozone are weaker than in oxygen. As a result, less energetic photons meaning those with longer wavelengths can break apart ozone molecules.
  • Oxygen molecules have stronger bonds, so they can only absorb a small range of higher energy, shorter wavelength UV light.
  • Ozone have weaker bonds, so they can absorb a broader range of wavelengths, including lower energy, longer wavelength UV light.
25
Q

Formal Charge= ?

A

Number of valence electrons- 0.5 (number of bonding electrons)- number of non-bonding electrons.

26
Q

Which Lewis structure is preferred?

A
  • The difference in FC of the atoms is closest to zero.
  • Has negative charges located on the most electronegative atoms.
27
Q

Describe the features of a sigma bond.

A
  • Sigma is always a single bond.
  • Looks like a sphere on the bond axis
  • As long as the overlap is on the bond axis, there will be a single bond.
  • Sigma always exists (depends on which plane viewed from).
28
Q

Describe the features of a pi bond.

A
  • Comes from two neighbouring p-orbitals
  • Electron density is above or below the bond axis.
  • All double and triple bonds are pi bonds.
29
Q

What is hybridisation?

A

The concept of mixing atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds in valence bond theory.

30
Q

Describe how hybridisation happens in a carbon atom.

A
  • If you provide a bit of energy you can promote (lift) one of the s electrons into a p orbital. The configuration is now 1s2, 2s1, 2p3.
  • The process is favourable because of the arrangement of electrons- four unpaired and with less repulsion is more stable.
  • The four orbitals (a s and 3 p’s)combine or hybridise to give four new orbitals. All four orbitals are equivalent.
31
Q

Why do alkanes have a tetrahedral arrangement?

A

The four sp3 orbitals repel each other into a tetrahedral arrangement.

32
Q

Why do alkenes have a planar arrangement?

A

The three sp2 orbitals repel each other into a planar arrangement and the 2p orbital lies at right angles to them.

33
Q

What is the arrangement of sp3?

A

Tetrahedral

34
Q

What is the arrangement of sp2?

A

Trigonal planar

35
Q

What is the arrangement for sp?

A

Linear

36
Q

What is the bond angle of a linear molecule?

A

180°

37
Q

What is the bond angle of trigonal planar?

A

120°

38
Q

What is the bond angle of a bent molecule?

A

118°

39
Q

What is the bond angle of a tetrahedral molecule?

A

109.5°

40
Q

What is the bond angle of a pyramidal molecule?

A

107°

41
Q

What are the bond angles of trigonal bipyramidal?

A

120° and 90°

42
Q

What are the bond angles of seesaw?

A

118° and 90°

43
Q

What is the bond angle of octahedral?

A

90°

44
Q

What is the bond angle of square pyramid?

A

87°

45
Q

What is the bond angle of T shaped?

A

87°

45
Q

What is the bond angle of square planar?

A

90°

Chemistry (10 decks)

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