Define a covalent bond.
Sign in and upgrade to Premium to write and mark your own answer.
the strong electrostatic attraction; between two nuclei and the shared pair of electrons between them
Covalent Bonding
Explain how electron density maps provide evidence for covalent bonding.
Sign in and upgrade to Premium to write and mark your own answer.
they show a region of increased electron density located between the two nuclei; this confirms that electrons are shared between the bonded atoms rather than transferred
Describe what is meant by a dative covalent bond.
Sign in and upgrade to Premium to write and mark your own answer.
a covalent bond in which both shared electrons originate from the same atom; one atom donates a lone pair to an empty orbital on another atom
State the species that donates the lone pair when NH₄⁺ forms from NH₃ and H⁺.
Sign in and upgrade to Premium to write and mark your own answer.
NH₃ / the nitrogen atom in ammonia
Explain how the dative bonds in Al₂Cl₆ form.
Sign in and upgrade to Premium to write and mark your own answer.
each aluminium atom in AlCl₃ has an empty orbital; a chlorine atom from another AlCl₃ unit donates a lone pair into this empty orbital; two such dative bonds form, joining the two AlCl₃ units into the dimer Al₂Cl₆
Explain why diamond is suitable for use in cutting tools.
Sign in and upgrade to Premium to write and mark your own answer.
diamond has a rigid three-dimensional lattice of carbon atoms; each carbon forms four strong covalent bonds in a tetrahedral arrangement; large amounts of energy are needed to break these bonds, giving extreme hardness
State two reasons why graphite conducts electricity but diamond does not.
Sign in and upgrade to Premium to write and mark your own answer.
each carbon in graphite forms only three covalent bonds, leaving one delocalised electron per atom; these delocalised electrons can move along the layers/in diamond all four outer electrons are localised in covalent bonds, leaving no free electrons
Suggest one application of graphene and explain why graphene is suited to that use.
Sign in and upgrade to Premium to write and mark your own answer.
flexible electronics / transistors / composite materials; graphene is strong, transparent, and conducts electricity due to its delocalised electrons in a one-atom-thick layer
Define electronegativity.
Sign in and upgrade to Premium to write and mark your own answer.
the ability of an atom; to attract the bonding pair of electrons in a covalent bond
Explain why electronegativity increases across Period 2 from lithium to fluorine.
Sign in and upgrade to Premium to write and mark your own answer.
nuclear charge increases across the period; shielding by inner electrons stays roughly the same; the bonding pair is attracted more strongly to the nucleus
Explain why ionic and covalent bonding can be considered as extremes of a bonding continuum.
Sign in and upgrade to Premium to write and mark your own answer.
when atoms have equal electronegativity, electrons are shared equally giving a pure covalent bond; a small electronegativity difference produces a polar covalent bond with partial charges δ⁺ and δ⁻; as the electronegativity difference increases, ionic character increases; if the difference is large enough, electrons are effectively transferred, giving an ionic bond
Suggest why MgCl₂ is regarded as ionic with some covalent character.
Sign in and upgrade to Premium to write and mark your own answer.
the electronegativity difference between Mg and Cl is large enough for the bond to be predominantly ionic; the small, highly charged Mg²⁺ ion polarises the Cl⁻ ion, distorting its electron cloud and giving the bond some covalent character
Distinguish between a polar bond and a polar molecule.
Sign in and upgrade to Premium to write and mark your own answer.
a polar bond has a permanent dipole due to a difference in electronegativity between the two bonded atoms; a polar molecule has an overall net dipole because its bond dipoles do not cancel due to molecular shape
CO₂ contains polar bonds but is non-polar overall. Explain.
Sign in and upgrade to Premium to write and mark your own answer.
oxygen is more electronegative than carbon, so each C=O bond is polar with O carrying δ⁻ and C carrying δ⁺; CO₂ is a linear molecule; the two equal bond dipoles point in opposite directions and cancel, giving zero net dipole
Predict, with reasoning, whether NH₃ is a polar molecule.
Sign in and upgrade to Premium to write and mark your own answer.
nitrogen is more electronegative than hydrogen, so each N–H bond is polar; NH₃ has a trigonal pyramidal shape due to a lone pair on N; the bond dipoles do not cancel and a net dipole points towards N, so NH₃ is polar
The compounds CO₂, H₂O, and CCl₄ all contain polar covalent bonds. Discuss the overall polarity of each molecule. In your answer you should: identify the polar bonds in each molecule, describe the shape of each molecule, explain whether the bond dipoles cancel, and conclude whether each molecule is polar overall.
Sign in and upgrade to Premium to write and mark your own answer.
C=O bonds are polar because oxygen is more electronegative than carbon (ΔEN ≈ 1.0); O–H bonds are polar because oxygen is more electronegative than hydrogen (ΔEN ≈ 1.4); C–Cl bonds are polar because Cl is more electronegative than C (ΔEN ≈ 0.5) CO₂ is linear; H₂O is bent/V-shaped; CCl₄ is tetrahedral in CO₂ the two equal bond dipoles point in opposite directions and cancel; in H₂O the bent shape means the two O–H dipoles do not cancel; in CCl₄ the symmetrical tetrahedral arrangement means the four equal C–Cl dipoles cancel CO₂ is non-polar overall; H₂O is polar overall with a net dipole towards O; CCl₄ is non-polar overall