BONDING Flashcards
(40 cards)
State the structure of, and bonding in, silicon dioxide. Other than a high melting point, give two physical properties of silicon dioxide that are characteristic of its structure and bonding.
(4)
Structure: Macromolecular / giant molecule / giant covalent
Bonding: Covalent / giant covalent
Physical Properties:
Any two from: Hard/ Brittle / not malleable Insoluble Non conductor
Give the formula of the species in a sample of solid phosphorus(V) oxide. State the structure of, and describe fully the bonding in, this oxide.
(4)
Formula: P4O10
Structure: Molecular
Bonding: Covalent / shared electron pair
van der Waals’ / dipole–dipole forces between molecules
Explain why magnesium has a higher melting point than sodium.
(3)
more protons (1) (or Mg2+ more charge than Na+) attracts delocalised (or bonding) electrons more strongly (1) Metallic bonding is stronger
Why do diamond and graphite both have high melting points?
(2)
macromolecular (1) strong covalent bonds (1)
Why is graphite soft?
(2)
Planes (1) weak (bonds) forces between planes (1)
The table below shows the melting points of some sodium halides.
NaCl NaBr NaI
Melting point /K 1074 1020 920
Suggest why the melting point of sodium iodide is lower than the melting point of sodium bromide.
(1)
Iodide / I– bigger (ion) (so less attraction to the Na+ ion)
Fluorine reacts with bromine to form liquid bromine trifluoride (BrF3). State the type of bond between Br and F in BrF3 and state how this bond is formed.
(2)
Covalent
Shared pair(s) of electrons / one electron from Br and one electron from F
When H+ ions react with H2O molecules, H3O+ ions are formed.
Name the type of bond formed when H+ ions react with H2O molecules. Explain how this type of bond is formed in the H3O+ ion. (2)
Dative (covalent)/coordinate
(Lone) pair/both electrons/two electrons on O(H2) donated (to H+) OR pair/both electrons come from O(H2)
Explain why the AsCl4+ ion has a bond angle of 109.5* (As in group 5)
There are 4 bonds or 4 pairs of electrons (around As)
(Electron pairs / bonds) repel equally
what is the meaning of the symbol δ+
Electron deficient
Methanol has the structure
Explain why the O–H bond in a methanol molecule is polar.
Oxygen more electronegative than hydrogen
causes higher e– density round oxygen atom / causes Hδ+ Oδ–
Suggest why the electronegativity of the elements increases from lithium to fluorine.(2)
More protons / bigger nuclear charge
Same or similar shielding
Name the crystal type which describes an iodine crystal
molecular
Describe the bonding in a crystal of iodine.
Van der Waals’ between molecules (1)
In terms of the intermolecular forces involved, suggest why
(i) hydrogen fluoride requires more heat energy for melting than does hydrogen chloride,
H-Bonding in HF (1)
(dipole-) dipole in HCl (1)
H-bonding is stronger than dipole-dipole or V.dW (1)
In terms of the intermolecular forces involved, suggest why
hydrogen iodide requires more heat energy for melting than does hydrogen chloride
HI bigger molecule than HCl (1)
OR more electrons
Therefore the forces between HI molecules are stronger (1)
Explain how the strongest type of intermolecular force in liquid HF arises.
large difference in electronegativity between H and F
δ+H-Fδ- dipole created or dipole clearly implied
attraction/bond formed between δ+H and lone pair on F
Explain the trend in the boiling points of the hydrogen halides from HCl to HI.
HCl HBr HI
Boiling point / K 188 206 238
van der Waals’ / induced/temporary dipole-dipole attractions
increase with the increasing Mr / size / mass / number of electrons (in the hydrogen halides)
Silicon tetrafluoride (SiF4) is a tetrahedral molecule.
Deduce the type of intermolecular forces in SiF4
Explain how this type of intermolecular force arises and why no other type of intermolecular force exists in a sample of SiF4
Van der Waals forces
(Uneven distribution of electrons in) one molecule induces dipole in neighbouring/another molecule
symmetrical molecule / dipoles cancel
OR
no hydrogens bonded to F (N or O), therefore no hydrogen bonding
The boiling points of fluorine and hydrogen fluoride are –188 °C and 19.5 °C respectively. Explain, in terms of bonding, why the boiling point of fluorine is very low.
VdW / van der Waals forces between molecules
IMF are weak / need little energy to break IMF / easy to overcome IMF
The bond angle around the oxygen atom in methanol is slightly smaller than the regular tetrahedral angle of 109.5°
Explain why this bond angle is smaller than 109.5°
Idea that lone pairs have greater repulsion than bonding pairs
Explain how permanent dipole-dipole forces arise between hydrogen chloride molecules.
Difference in electronegativity leads to bond polarity
(dipoles don’t cancel therefore the molecule has an overall permanent dipole) and there is an attraction between ∂+ on one molecule and ∂− on another
Van der Waals’ forces exist between all molecules.
Explain how these forces arise.
Electron movement in molecule causes temporary dipole/uneven distribution of electrons
Induces a dipole in another molecule
δ+ attracts δ- in different/adjacent molecules
Phosphine (PH3) has a structure similar to ammonia.
In terms of intermolecular forces, suggest the main reason why phosphine is almost insoluble in water.
(Phosphine) does not form hydrogen bonds (with water)
