Bonding: Part 2 Flashcards
What is electronegativity?
The ability of an atom to attract the bonding electrons towards itself in a covalent bond
In a covalent bond, with identical atoms how are the bonding electrons distributed?
Equally
What are non-polar bonds?
When both atoms have the same electronegativity, bonding electrons are evenly distributed between bonded atoms
What are polar covalent bonds?
Bonding electrons are more attracted the more electronegative atom. As the electron cloud is more dense around the more electronegative atom there is a permanent dipole across the bond. Polar covalent because of the permanent dipole
What is a permanent dipole?
A small difference in electronegativity across a bond resulting from a difference in electronegativities of bonded atoms
General trend of electronegativity in periodic table
Increases towards the top right
Most electronegative element
Fluorine
Covalent bond electronegativity
0
Polar covalent bond electronegativity
1.8 ≥ 0
Ionic bond electronegativity
≥ 1.8
What type of bond do symmetrical molecules contain?
Non-polar, dipoles cancel out
What type of bond do non-symmetrical molecules contain?
Polar bonds because the dipoles don’t cancel out
What are intermolecular forces?
Attractive forces between molecules that are weaker then ionic or covalent bonds, and only found in covalent structures
What are London/induced dipole-dipole forces?
Very weak intermolecular forces between molecules, all covalent structure non-polar or polar
How do london forces arise between molecules?
At any moment, there may be an uneven distribution of electrons in a molecule due to movement or change in their density, causing a temporary/instantaneous dipole. The instantaneous dipole in one molecule causes an induced dipole in the neighbouring molecule. Dipoles attract producing weak attractive force
What are permanent dipole-dipole interactions?
Weak attractive forces between polar molecules. One of the atoms is more electronegative so a permanent polar bond is present, asymmetry causes them not to cancel out. Dipole attract to produce a weak electrostatic force of attraction between molecules
Which is th stronger permanent or induced dipole-dipole attractions?
Permanent dipole-dipoles
What are hydrogen bonds?
A strong dipole-dipole attraction between molecules contains O-H, N-H OR F-H. Exists between a H+ dipole atom in one molecule and a lone pair on a highly electronegative atom of another molecule.
What type of intermolecular force of attraction is the strongest?
A hydrogen bond
Anomalous properties of water
-Ice is less dense than water because molecules are held far apart by the hydrogen bonds, gives ice an open lattice structure. They are fixed in their positions by these H bonds
-Water has relatively high melting and boiling point
-Relatively strong so need lots of energy to overcome
