Chemical Bonding Flashcards
Definite metallic bonding
Metallic bonding is the electrostatic attraction between positively charged cations and the sea of delocalised negatively charged electrons
Factors affecting strength of metallic bonding
- number of valence electrons contributed to sea of delocalised electrons (by higher charged cations)
- size of cation (smaller size of cation, stronger metallic bond)
Define ionic bonding
Ionic bond is the electrostatic forces of attraction between oppositely-charged ions
What factors affect coordination number?
Coordination number is the number of ions that surround another ion of opposite charge.
Factors:
1. Cationic and anionic radius. (larger cationic radius, more anions can surround, higher coordination number)
2. Cation to Anion ratio
Factors affecting strength of ionic bond
lattice energy= q+q-/r+ + r-
Factors determining covalent character in ionic bonds
- higher charge density of cation = charge/cationic radius.
- higher charge density, higher polarising power - larger electron cloud of anion (more electrons or larger anionic radius), the anion is more easily polarised
-AlCl3, AlBr3 and many Be compounds are covalent
Define covalent bonding
Covalent bonding is the electrostatic forces of attraction between a shared pair of electrons and positively-charged nucleus.
Draw bonding in Al3Cl6 and ammonium ion
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Criteria for dative bond
Donor atom has lone pair of electrons
Acceptor atom is electron deficient
State the shapes and bond angles for species
2EP:
2 bp –> Linear, 180
3EP:
3 bp –> trigonal planar, 120
2 bp, 1 lp –> bent, 110-120
4EP:
4 bp –> tetrahedral , 109.5
3 bp, 1 lp –> trigonal pyramidal, 107
2 bp, 2 lp –> bent, 105
5EP:
5 bp –> trigonal bipyramidal, 90&120
4 bp, 1 lp –> see-saw, 90&120
3 bp, 2 lp–> T-shaped, 90&120
6EP:
6 bp–> octahedral, 90
5 bp, 1 lp–> square pyramidal, 90
4 bp, 2 lp –> square planar, 90
State the VSEPR theory
-Electrons are negatively-charged and repel each other. Hence electron pairs around the central atom of a molecule are arranged as far apart as possible to minimise electrostatic repulsion and maximise stability
- Lone pair of electrons are closer to central atom and repel more than bonding electrons. Hence lplp repulsion > bplp repulsion > bpbp repulsion
Explain the effect of electronegativity on bond angle. Taking H2O and H2S as an example.
- Both H2O and H2S are covalent molecules with 2 bond pairs of and 2 lone pairs of electrons.
- In H2O, O has a greater electronegativity than S in H2S.
- Hence, the bond pair of electrons
are attracted closer to the central atom O, resulting in greater repulsion between thebond pairs of electrons of O in H2O. - Hence, H2O has a larger bond angle than H2S.
Explain the difference in C-C bond length
A sp3 hybrid orbital has more p character than a sp2 hybrid orbital and it is longer/more diffuse. Hence, a sp3 hybrid orbital undergoes less effective overlap, giving rise to longer
bond length and weaker bond.
Explain how idid attractions arise
- As electrons are constantly moving, there could be instantaneous dipole formed when there are more electrons formed on one side of the molecule. Hence there could be a small partial positive charge on one atom and small partial negative charge on the other atom.
- When a neighbouring molecule approaches, this instantaneous dipole induces a temporary dipole on the neighbouring molecule by attracting or repelling its electrons.
- This intermolecular forces of attraction between 2 molecules of opposite partial charged are called idid.
Explain factors affecting covalent bond strength. (covalent bond between atoms !)
- effectiveness of overlap of orbitals
(size of atomic orbital) smaller atoms can approach each other more closely, more effective overlap, stronger bond and shorter bond length - bond order
triple bond>double bond>single bond - bond polarity
greater EN diff, more polar bond, stronger the bond
Factors affecting idid attractions
- Number of electrons
more electrons, more polarisable electron cloud, stronger idid - Larger surface area, stronger idid
Explain how pdpd arise
When two different atoms of different EN come together, the more EN atom pulls the bonding electron of the covalent bond towards itself and acquire a small positive charge while the other acquires a small negative charge. This results in charge separation and bond is polar.
criteria for hydrogen bonding
- HO, HF or HN in one molecule
- lone pair of electrons on F, O, N molecule
factors affecting hydrogen bond
- Extensiveness of hydrogen bonds (number of hydrogen bonds formed per molecule)
- EN diff between H and F,O or N
(F more EN than O and N, forming more polar H-F bond than H-O and
H-N, hence stronger H bond)
Intramolecular hydrogen bond arising from close proximity of substituents, leading to less extensive intermolecular hydrogen bonding hence lesser energy to…
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Characteristics, structure, shape, bond angle of diamond
- Each carbon atom is covalently bonded to 4 other carbon atoms (4 σ bonds) arranged tetrahedrally around it, with a bond angle of 109.5
- Diamond does not conduct electricity as it does not possess delocalised electrons.
- Diamond has a melting point of 3550 due to the strong covalent bonds between all the carbon atoms.
- Diamond does not dissolve in water or any other solvent as a lot of energy is required to overcome the strong covalent bonds between the carbon atoms.
Explain the structure and properties of ice
- When temperature is low at 0oC, the kinetic energy of the H2O molecules is low and do not move around that readily. Each O atom in H2O is tetrahedrally bonded to four hydrogen atoms, two by covalent bonds and two by intermolecular hydrogen bonds, giving rise to a highly ordered 3–D structure in ice.
- This highly ordered 3–D arrangement of H2O molecules in ice creates a very open
structure that occupies a larger volume for the same mass of liquid water. - Hence ice is less dense than liquid water.
Why graphite can conduct electricity
- Each carbon atom is covalently bonded to 3 other carbon atoms (3 σ bonds) arranged in a trigonal planar manner, with a bond angle of 120.
- Each carbon is sp2 hybridised and has an unhybridised p-orbital containing 1 electron. The p orbital of each adjacent carbon atom will overlap sideways, resulting in a pi-
electron cloud above and below the plane containing the carbon atoms. - These pi-electrons are delocalised within each layer and hence, graphite only conduct electricity in a direction parallel to the layers. As the delocalised electrons cannot jump
across the layers, graphite is an insulator in a direction perpendicular to the layers.
