chem bonding Flashcards
Factors affecting id-id (Electron cloud size)
Electron cloud size
The strength of instantaneous dipole–induced dipole interactions increases with the number of electrons in a molecule.
* Larger electron clouds are more easily polarised / distorted than smaller electron clouds, resulting in the greater ease of formation of instantaneous dipoles and induced dipoles
The halogens from F2 to I2 are non-polar, and so the attraction between their molecules is due to instantaneous dipole–induced dipole (id−id) interactions.
The number of electrons of the halogens increases down the group from F2 to I2.
Ease of polarisability of electron clouds and strength of id-id interactions also increase down the group, with I2 having the strongest id–id interactions.
Since more energy is required to break stronger intermolecular interactions, the boiling points of halogens increases down the group.
Factors affecting id-id (surface area for molecular interactions)
Straight–chained hydrocarbons have greater surface areas for intermolecular interactions compared to branched isomers, and so instantaneous dipole–induced dipole interactions are stronger in straight–chained hydrocarbons.
ionic bond
An ionic bond is an electrostatic attraction between cations and anions in an ionic lattice.
giant molecular structure
A solid with a giant molecular lattice structure is made up of atoms held together in an extensive network by strong covalent bonds. Such solids are said to have giant covalent structures and are macromolecules.
Factors Affecting Metallic Bond Strength in a Giant Metallic Lattice
Number of valence electrons available:
➢ Generally, the greater the number of valence electrons, the stronger the bonds.
➢ Magnesium, with 2 valence electrons, has stronger metallic bonds than sodium, with only one valence electron.
(ii) Charge of cations
➢ The higher the charge of cations, the stronger the bonds.
➢ Magnesium, with its metal cations having a charge of 2+, has stronger metallic bonds than sodium, with its metal cations having a charge of 1+.
(iii) Size of cations:
➢ For the same type of packing, the smaller the size, the stronger the bonds.
➢ A smaller cation has a higher charge density ( charge / volume) and thus greater electrostatic attraction for the delocalised electrons
Covalent Bond
A covalent bond is the electrostatic attraction
between the shared pair of electrons and the
positively charged nuclei
VSEPR Theory
Electron pairs (bond pairs and lone pairs) around the central atom of a molecule are arranged as far apart as possible in space to minimise their mutual repulsion.
➢ Lone pair-lone pair > lone pair-bond pair > bond pair–bond pair
repulsion repulsion repulsion
extensiveness of H-bond using NH3 and H2O to explain
H2O has a higher boiling point than NH3 due to the more extensive hydrogen bonding in H2O compared to NH3. H2O molecules form an average of 2 H−bonds per molecule of H2O while NH3 molecules form an average of 1 H−bond per molecule of NH3.
NH3 vs HF
- Both NH3 and HF form an average of one hydrogen bond per molecule.
- The dipole moment of the H–X bond is greater for H–F than for H–N since F is more electronegative than N. The larger the dipole moment, the stronger the hydrogen bond, thus the hydrogen bonds between HF molecules are stronger than those between NH3 molecules.
- Thus, more energy is needed to overcome the stronger H–bonds between HF molecules than
NH3 molecules. HF has a higher boiling point than NH3
Covalent Bond Length definition
The covalent bond length is the distance between the nuclei
of two bonded atoms.
* Generally, the stronger the covalent bond, the shorter is the bond length.
Explain id-id interactions
Electrons are constantly moving and at any given moment, the electron density of a phosgene molecule can be unsymmetrical, resulting in an instantaneous dipole, which induces a short-lived dipole in a neighbouring phosgene molecule, hence resulting in id-id interactions
explain pd-pd interactions
Phosgene molecules are polar with permanent dipoles in their structures. Pd-pd interactions arise due to the electrostatic attraction between the 8+ end of one phosgene molecule and the 8– end of the other phosgene molecule.
Factors affecting covalent bond strength (effectiveness of orbital overlap)
As the halogen increases in size, the valence orbital used in bonding is more diffuse.
Hence, the overlap of the orbitals is less effective from chlorine to iodine and bond energy decreases from chlorine to iodine.
factors affecting covalent bond strength (number of bonds)
For the same bonding atoms, an increase in the number of bonds increases the number of shared electrons between the two atoms i.e. there is increased electrostatic attraction between the bond
pairs and the two nuclei, hence bond strength is increased
Factors affecting covalent bond strength (difference in EN)
In general, the greater the difference in electronegativity, the more polar the covalent bond (i.e. greater the bond polarity) and the stronger the bond.
Metallic bond
Electrostatic attraction between a lattice of positive ions and delocalised electrons
Factors affecting strength of id-id interactions
1) electron cloud size
- no of electrons increase, electron cloud size becomes larger and more polarisable, id-id interactions between molecules become stronger, more energy required to break intermolecular interactions
2) surface area for molecular interactions
- straight-chained hydrocarbons have greater surface area for molecular interactions compared to branched isomers, so id-id interactions are stronger
Factors affecting strength of pd-pd interactions
Strength of pd-pd interactions increases with increasing dipole moments
