Bonding - Covalent Flashcards
Define covalent bonding
The electrostatic attraction between the nuclei of two atoms and one or more shared pairs of electrons between them
Double bond
Where two pairs of electrons are shared
Triple bond
Where three pairs of electrons are shared
Features of a valence structure
Bonding pairs shown as lines, non-bonding electrons shown as dots
Features of a Lewis structure
All valence electrons shown as dots (bonding and non-bonding)
Features of a structural formula
Bonding pairs shown as lines, no lone pairs shown
Shape of methane (CH4)
Tetrahedral (4 bonding groups, no lone pairs)
Shape of ammonia (NH3)
Trigonal pyramidal (3 bonding groups, one lone pair)
Shape of water (H2O)
Bent (2 bonding groups, 2 lone pairs)
Shape of boron trichloride (BCl3)
Trigonal planar (3 bonding groups, no lone pairs)
Shape of carbon dioxide (CO2)
Linear (2 bonding groups, no lone pairs)
Shape around each C in ethane (C2H6)
Tetrahedral (4 bonding groups, no lone pairs)
Shape around each C in ethene (C2H4)
Trigonal planar (3 bonding groups, no lone pairs)
What features make a molecule polar?
Polar bonds, arranged asymmetrically in the molecule
Why is diamond hard?
4 strong covalent bonds per atom, arranged tetrahedrally
Why doesn’t diamond conduct electricity?
As the valence electrons are fixed within bonds, there are no free-moving charged particles to move and carry charge
Why is graphite soft?
The layers of carbon atoms can slide past each other easily
Why can graphite conduct electricity?
Graphite contains delocalised electrons which can move and carry charge
Why does PCl3 have a much higher boiling point than BCl3?
PCl3, a polar molecule, is able to form dipole-dipole forces and dispersion forces between molecules, whereas non-polar BCl3 is only able to form dispersion forces. As dipole-dipole forces are stronger than dispersion forces, it takes more energy to break the intermolecular forces between PCl3 molecules than BCl3 molecules
Why does octane (C8H18) have a higher boiling point than pentane (C5H12)?
Because octane has more electrons than pentane (66 vs 42) and has a larger surface area between molecules, it is able to form stronger dispersion forces between molecules and requires more energy to disrupt these forces.
Why does diamond have a much higher boiling point than water?
Diamond has strong covalent bonds between all of its atoms, which take lots of heat energy to disrupt. In comparison, the hydrogen bonds and dispersion forces between water molecules are relatively weak and can be disrupted using less energy.
Why is the bond angle in ammonia (107) lower than that in methane (109.5)?
The lone pair in ammonia repels other valence shell electron pairs more effectively than the bonding pairs do. As a result, the bonding pairs in ammonia are pushed closer together than those in methane, which does not contain a lone pair.
What three types of substance dissolve well in water?
Polar molecules, molecules that ionise, soluble ionic compounds
What two properties affect the distance a component travels in paper chromatography or TLC?
Solubility in the mobile phase, and strength of adsorption to the stationary phase.
What forces exist between the molecules of any hydrocarbon substance?
Dispersion forces (only)
How does a dative covalent bond form?
Both shared electrons are contributed by one of the bonding atoms.
How many lone pairs of electrons exist in hydrogen cyanide, HCN?
One (on the nitrogen - draw out the dot-cross diagram to be sure)
Explain why tetrachloromethane, CCl4, is non-polar.
The four polar C-Cl bonds in CCl4 have polarities which cancel each other out as they are arranged symmetrically.
Between what two molecules would a dispersion force arise?
Between an instantaneous dipole and an induced dipole
Between what two molecules would a dipole-dipole force arise?
Between two permanent dipoles (polar molecules)
Between what two molecules would a hydrogen bond arise?
Between one molecule containing H bonded to nitrogen/oxygen/fluorine, and another containing a delta-negative nitrogen/oxygen/fluorine.
Why is buckminster fullerene (C60) considered a simple molecular substance?
The particles have a defined number of atoms (in this case, 60).
Why are dispersion forces weaker than dipole-dipole forces?
Dispersion forces only arise between two temporary dipoles, so they are by nature temporary forces. On the other hand, dipole-dipole forces arise between permanent dipoles so they are much more permanent in nature.
Not a question - be sure that you can draw any diagrams that appear in the topic, including those that show molecule shape, those that show bonding within and between molecules or ions, those that show structure of giant covalent substances etc.
I understand.
Not a question - be sure that you can write balanced equations and ionic equations, as necessary, for any of the reaction types described during the topic.
I understand.
