Chapter 6 Flashcards
4: 0
tetrahedral
109.5
3: 1
pyramidal
107
2: 2
non-linear
104.5
2 areas of electron density
linear
3 areas of electron density
trigonal planar
4 areas of electron density
tetrahedral
5 areas of electron density
bi-pyramidal
6 areas of electron density
octahedral
what is electronegativity
the attraction of a bonded atom for the pair of electrons in a covalent bond
What is a dipole
A separation of opposite charges within a molecule.
Permanent dipole
This is a dipole in a covalent bond and it doesn’t change.
Polar solvents and solubility
Since H2O is also a polar molecule, any polar solvents can also dissolve in it. The water molecules attract the ions and the lattice breaks down
Covalent bonding
Strong and they hold atoms in a molecule together
IMF
Weak interaction between dipoles of different molecules.
London forces
They exist between all molecules, polar or non-polar. They act between induced dipoles.
London forces depend on
The more the electrons in each molecule:
the larger the dipoles
the greater the London interaction
the stronger the attractive forces
Permanent dipole-dipole interactions
They act between the permanent dipoles in different polar molecules.
simple molecular substances and solubility
Simple molecular compound is added to a non-polar solvent, IMF form between the molecules and the solvent. The interactions weaken the IMF and they break down meaning it dissolves.
Electrical conductivity
There are no mobile charged particles in simple molecular structures.
With no charged particles that can move, there is nothing to complete an electrical circuit.
Where do hydrogen bonds occur
Between
H- O
H- F
H- N
what is an ionic bond
Electrostatic attraction between oppositely charged ions.
how are London forces created?
When 1 atom approaches another atom and the approaching atom’s electron shells repel the electrons of the other atoms’. This results in slightly exposing the nucleus of the other atom and it creates an electrostatic attraction between the electron shells of one atom and the exposed nucleus of the other atom. This creates a dipole, which then induces a dipole in the atom’s neighbouring atoms.
They are being broken and remade all the time.
When is a molecule non-polar?
When the 2 atoms bonded are of the same element, so the difference in electronegativities is 0.
When is a molecule non-polar (ex. answer)?
If all the dipoles in a molecule are symmetrical, then the dipoles in the molecules cancel each other out. Because the molecule has no net dipole, it is now non-polar.
When is a molecule polar (ex. answer)?
If all the dipoles are not of equal magnitude and not directly opposing each other, it means the dipoles are asymmetrical. Hence, the dipoles can’t cancel each other out, leaving the molecule with a net dipole and hence the molecule is polar.
How does electronegativies change in the Periodic Table?
Decreases down the group.
Increases as you move across a period.
Why does electronegativities decrease down a group?
Because as you go down a group, you increase the atom’s radius, and you increase the amount of electron shielding. This reduced the attraction between the valence electron and nucleus.
Why does electronegativity increase across a period?
Elements have the same number of shells, but they increase in number of protons in the nucleus. This increase the effective nuclear charge, and also increases the attraction between the nucleus and the valence electron.
The larger the EN…
The larger the dipole.
How are simple molecular lattices held together.
The atoms are held by strong covalent bonds, and then the molecules are held together by weaker IMF.
Why do simple molecular lattices have small melting and boiling points?
Because it doesn’t require much energy to break the weak intermolecular forces.
What is the solubility of simple molecular lattices?
They have weak dipoles and tend to be soluble in non-polar solvents and insoluble in water.
