Structure and bonding Flashcards
What is covalent bonding?
Covalent bonds are held together by electrostatic forces of attraction between positively charged nuclei and negatively charged shared electrons.
What is a covalent network structure?
A covalent network structure consists of a giant network of covalently bonded atoms.
If two atoms have the same electronegativity, what will happen?
The electrons will be shared equally therefore it is a non-polar covalent bond.
If one atom has a slightly higher electronegativity than the other what will happen?
The atom with the greater electronegativity will have the bonding electrons closer to it making that atom slightly negative and the other atom slightly positive. This is know as a polar covalent bond.
What will happen is one atom has a massive difference in electronegativity to another?
The atom with the greatest electronegativity will have the bonding electrons pulled so close to it that in effect it has gained those electrons and the other atoms have lost those electrons making it an ionic bond.
What are the three structures that compounds may be in a solid state?
- Ionic
- Covalent network including silicon dioxide and silicon carbide
- Covalent molecular
What are the 4 duffest types of arrangement of a compound?
- Linear
- Angular
- Trigonal Pyramidal
- Tetrahedral
What is intermolecular bonding?
Intermolecular bonding are bonding between molecules.
What is intramolecular bonding?
Intramolecular bonding are bonding within molecules
Why are some compounds with the presence of polar bonds not a polar molecule?
Because the molecule is not symmetrically arranged.
What are the main examples of non-polar molecules?
- Hydrocarbons
- Carbon dioxide
What are the main examples of polar molecules?
- Organic compounds such as ethanol
- water
How do you test the polarity of a liquid?
Rubbing a plastic rod creates an electric charge which can be used to attract objects. Since polar molecules have a permanent dipole, they will be attracted to the rod. Non-polar molecules are not affected by the charged rod.
What are London dispersion forces?
London dispersion forces are the weakest of the intermolecular forces but in the absence of any other any they are important (I.e. holding a polar bond together)
What is the relationship between the number of electrons and the strength of the London dispersion forces?
The greater number of electrons there are present in a molecule, the stronger the London dispersion forces are.
What are permanent dipole to permanent dipole interaction?
Molecules which are polar will have a permanent dipole. The permanent dipole interactions between such molecules are an additional electrostatic attraction holding the molecules together. This accounts for the higher melting and boiling points os substances which have a similar number of electrons
What are hydrogen bonds?
Hydrogen bonding is the strongest toe of intermolecular bonding. Hydrogen atoms have a very low electronegativity. If hydrogen is bonded to a very electronegativity atoms (e.g. oxygen, nitrogen or fluorine) then the covalent bond will be very polar with the result that H will be slightly positive which will attract the slightly negative N, O or F.
What is the relationship between polar molecules with solubility?
Polar and ionic substances dissolve in polar solvents. The more polar a substance is, he more soluble it is in a polar substance
What is the relationship between non-polar molecules with solubility?
Non-polar substances will dissolve in non-polar solvents.
Why is it that like dissolves with like?
This is because the solvent can form bonds with the solute.
What is the relationship with hydroxyl groups and solubility?
Molecules with a hydroxyl group can form hydrogen bonds with water. The more hydroxyl groups that are present, the more soluble the molecule is in water.
What is the relationship between the strength of intermolecular bonds and viscosity?
The stronger the intermolecular bonds, the more viscous the liquid is. Remember the number of electrons will contribute to this.
What is the relationship between hydroxyl groups and viscosity?
The more hydroxyl groups that are present, the more hydrogen bonds that are formed therefore the higher the viscosity.
What happens with hydrogen bonding in ice?
As water cools, the kinetic energy of the molecule decreases and the density increase. At 4 degrees Celsius, the water molecules are moving with a low enough kinetic energy that hydrogen bonds can permanently form and hold the water molecules in a fixed position. The open lattice that forms as water freezes to solid ice is less dense than liquid water so ice floats on water.
