chapter 4: bonding Flashcards
how does the strength of a coordinate bond differ from a covalent bond?
the strength of a coordinate bond is the same as other bonds as once the coordinate bond is formed, it is the same as any other covalent bond
why is ionic bonding referred to as ‘non-directional’?
the electrostatic forces of attraction between the oppositely charged ions in the giant lattic structure are in all directions and not just between 2 atoms like in a covalent bond.
bonding of: propane, propanol, and propanoic acid
propane: alkane, is symmetrical, has LDF
propanol: can form H-H bonds
propanoic acid: carboxylic acids, can form H-H bods stronger than propanol
bond angle of O-Si-O in SiO2?
SiO2 has a tetrahedral giant structure, cannot be linear, bond angle is 109 degrees
benzene structures
how does a compound contain both ionic and covalent bonds?
non-metal bonded to a polyatomic ion
compounds that break the octet rule
SCl4, BCl3
characteristics of square planar
6ED, 2LP
a. explain why you would expect a BeF2 molecule to be linear but an SF2 molecule to be bent
b. why is the H-N-H angle in ammonia smaller than the H-N-H angle in the ammonium ion?
c. what is the bond angle and hybridisation in the C-C-C bond in benzene, C6H6?
d. what is the bond angle and hybridisation in the C-C-C bond in cyclohexane, C6H12?
a. BeF2 has 2 electron domains with no lone pairs, so it has a linear shape w bond angles of 180 degrees
SF2 has 4 electron domains w 2 lone pairs, so it has a bent shape w bond angles of about 105 degrees
b. ammonia molecule has a trigonal pyramidal shape due to its 4 electron domains and lone pair. the lone pair-bonding pair electron repulsion is stronger than the bonding pair-bonding pair electron repulsion and therefore pushes the bonding pair closer to each other. hence the H-N-H angle in ammonia is 107 degrees
ammonium ion has 4 electron domains, so the ion has a tetrahedral shape. the angle is 109.5 degrees
c. the carbon atoms have 3 electron domains and are sp2 hybridised, so the C-C-C bond angle in benzene is 120 degrees
d. the carbon atoms are sp3 hybridised and have 4 electron domains, so the C-C-C bond angle in cyclohexane is 109.5 degrees
explain why the 2 C-O bond lengths in propanoic acid, C2H5COOH, are different and yet the 2 C-O bond lengths in the propanoate anion, C2H5COO-, are the same length
in propanoic acid, the C-O bond lengths are different as one is a single covalent bond while the other is a double covalent bond
in propanoate ion, the C-O bond lengths are the same due to resonance resulting in equivalent C-O bonds where the negative charge is spread over the O-C-O bonds
why is the light required to break the O-O bond in oxygen of a higher frequency than the light required to break the O-O bond in ozone?
the O-O bond in oxygen is a double covalent bond whereas the O-O bond in ozone is between a double covalent bond and a single covalent bond due to its resonance. hence, O-O bond is stronger in oxygen than in ozone and requires more energy to break. higher frequency = higher energy, so higher frequency light required
why does penta 1,4-diene H2C=CH-CH2-CH=CH2 not contain any delocalised electrons whereas penta-1,3-diene, H2C=CH-CH=CH-CH3 does contain delocalised electrons?
the pi bonds in penta-1,4-diene are not next to a carbon atom with no free p orbitals and cannot be delocalised
the pi bonds in penta-1,3-diene are separated by a single covalent bond and can be delocalised
explain why at room temperature, F2 and Cl2 are gases, Br2 is a liquid and I2 is a solid
halogen molecules are non-polar, so halogens have LDF
size of halogens increases down the group, so the number of electrons increases. as the number of electrons increases, the LDF increases, hence the melting and boiling points increases
butane (-1 degrees C), propanone (56 degrees C), and ethanol (78 degrees C) have similar molar masses but different boiling points, explain the difference in boiling points between the three molecules
they have similar molar masses, so they have similar LDF strength.
butane is non-polar, only has LDF, low esfoa which require a low amount of energy to overcome, so lowest boiling point
propanone is polar, has dipole-dipole forces, higher boiling point
ethanol is polar and has hydrogen bonding, high esfoa which require a large amount of energy, highest bp
why does boiling point change down the group?
down the group, the number of valence electron shells and protons increases, so the esfoa due to the van der waals’ forces increases. hence, a larger amount of energy is required to overcome the bonds held together by these forces. so the boiling point increases.
