Bondings Flashcards
Ionic Bonding
? The electrostatic attraction between oppositely charged ions
Metallic Bonding
? Electrostatic attraction between delocalised electrons and positively charged metal ions
Covalent bonding
? Strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Dative Covalent bond
? One atom donates both of the electrons in the covalent bond. They are equivalent to other covalent bonds.
Electronegativity
? The power of an atom to attract a pair of electrons in a covalent bond.
? The measure of the attraction of a bonded atom for the pair of electrons in the covalent bond.
Non polar covalent bonds
? Forms when the atoms (made of the same element) have identical electronegativities
Polar covalent bonds
? Forms when the elements in the bond have different electronegativities (of around 0.3-1.7)
Intramolecular forces
? forces within molecules
Intermolecular forces
? forces between molecules
Hydrogen bonding
? Occurs between a hydrogen atom and a lone pair of electrons on a very electronegative atom. (H-O, H-N, H-F)
Melting point
? Is the temperature a species starts to melt which the same temperature the species starts to freeze
Boiling point
? Is the temperature a species starts to boil which is the same temperature the species starts to condense
Valence Shell electron pair repulsion theory (VSEPR)
? The shape adopted by a single molecule or ion is that which keeps repulsive force to a minimum.
electrons in the outer shell of atoms arrange themselves as far apart as possible to minimise repulsion
decrease by 2.5 degrees
The shape of: 2 electron pairs - both bonding pairs
Linear, 180 degrees
The shape and angle of 3 electron pairs - 3 bonding pairs
Trigonal planar 120 degrees
The shape and angle of 3 electron pairs - 2 bonding pairs & 1 lone pair
Bent, around 119 degrees
Order of strengths of repulsion
Lone-lone > Lone-bonding > bonding-bonding
4 electron pair; 4 bonding pairs
Tetrahedral, 109.5 degrees
4 electron pairs; 3 bonding pair, & 1 lone pair
Trigonal pyramidal, 107 degrees
4 electron pairs; 2 bonding pairs & 2 lone pairs
Bent, 104.5 degrees
How many degrees does a lone pair reduce the bond angle by?
Approximately 2.5 degrees
5 electron pairs; 5 bonding pairs
Trigonal Bipyramidal, 90/120 degrees
5 electron pairs; 4 bonding pairs& 1 lone pair
Sawhorse, <90/<120 Degrees
6 electron pairs; 6 bonding pairs
Octahedral, 90 degrees
6 electron pairs; 5 bonding pairs & 1 lone pair
Square pyramidal, < 90 degrees
Properties of Ionic Bonding
High MP/BP - oppositely charged ions
Conduct electricity -molten/aqueous
Brittle - - layers repel
Properties of metallic bonding
Conduct electricity - delocalised electrons
Malleable, ductile - layers can slide over each other without repulsion.
The strength of metallic bond depends on ….
Charge, ↑charge greater attraction
Size, smaller the metal ions closer the electrons is to the (+) nucleus, greater attraction
Trends in electronegativity down a group and across a period
Down a group - Electronegativity ↓, as atomic radius ↑, ↑shielding, ↑ distance between the nucleus and the bonding pair, ↓attraction.
Across a period, electronegativity ↑, atomic radius ↓, ↑nuclear charge, ↑ attraction between the nucleus and the bonding pair.
Types of intermolecular forces
Van der waals - Very weak (occurs at split seconds) Permanent dipole - if aligned correctly attraction Hydrogen Bonding - HN,HF,HO
How does hydrogen bonding give water unique properties?
- surface tension
- excellent solvent
- liquid at room temp
- highly polar molecule
- High MP/BP
What structure does ice have ?
tetrahedral. When ice melts, structures collapse slightly, molecules come close, then move a little apart as ↑ E.
Water has maximum density at 4 degrees
Formula for sulfate
SO4(2-)
Formula for hydroxide
OH-
formula for carbonate
CO3(2-)
formula for ammonium
NH4+
How can you represent co-ordinate bonds
Using an arrow
Describe the properties of diamond
- Very high melting point
- Strong - tetrahedral structure
- Non-conductor of electricity - no delocalised electron
Properties of graphite
- high MP
- Soft - hexagonal
- conductor of electricity
Properties of silicon dioxide/silica
- High MP
- Strong - silicon is joined to 4 oxygen
- non-conductor of electricity
What is a symmetric molecule
A symmetric molecule (all bonds identical and no lone
pairs) will not be polar even if individual bonds within
the molecular ARE polar.
describe how the electron distribution in a covalent bond between elements with different electronegativities will be unsymmetrical?
Permanent dipole-dipole forces occurs between polar molecules
•It is stronger than Van der Waals and so the compounds have higher boiling points
•Polar molecules have a permanent dipole. (commonly compounds with C-Cl, C-F, C-Br H-Cl, C=O bonds) •Polar molecules are asymmetrical and have a bond where there is a significant difference in
electronegativity between the atoms.
How do you show that a bond is polar
Partial charges
Can you explain why some molecules with polar bonds do not have a permanent dipole?
This is due to the symmetry in some polar molecules,so the dipoles cancel each other out. For example, water is a polar molecule, however, as water is negatively charged on one side and positively charged on the other, the charges cancel each other out
Can you explain the importance of hydrogen bonding in the low density of ice and the anomalous boiling points of compounds?
Ice is less dense than water because the orientation of hydrogen bonds causes molecules to push farther apart, which lowers the density.
The anomalously high boiling points of H2O,
NH3 and HF are caused by the hydrogen
bonding between the molecules
