Unit 1 - Structure and Bonding Flashcards
Rank these bonding types in order from least to most difference of electronegativity:
Polar covalent, ionic and pure covalent
1.Pure Covalent
2. Polar Covalent
3. Ionic
How can ionic bonds be formed?
When atoms with a large difference in electronegativity transfer electrons rather than share them.
True or False: The larger the difference in electronegativity, the more ionic in character the bond.
True
What do ionic compounds exist as?
Crystal lattice structures.
What is a covalent bond?
Where 2 positive nuclei share a common attraction for the negatively charged shared pair of electrons.
Explain hydrogen’s diatomic bonding.
The two atoms share electrons equally since each hydrogen atom has the same pull on the bonded electrons (same electronegativity).
What is a pure covalent bond/non-polar covalent bond?
When there is no difference in the electronegativity of the atoms. The electrons are shared equally and therefore there is no dipole in the bond.
What is a polar covalent bond?
When two atoms with different electronegativity values form covalent bonds resulting in an unequal sharing of electrons. This unequal sharing of electron leads to a dipole within the bond – an uneven distribution of charge. The atom with a higher electronegativity, pulls the electrons closer, making it slightly negative and leaving the other atoms slightly positive.
What do polar bonds have within them?
Permanent dipole
What is a permanent dipole?
A permanent unequal distribution of electrons in a bond.
Why does a molecules polarity depend on its arrangement?
Polar molecule contain polar covalent bonds which are not arranged symmetrically and so now negative poles and positive poles exist within the molecule (a permanent dipole).
Why does a molecules polarity depend on its arrangement?
Polar molecule contain polar covalent bonds which are not arranged symmetrically and so now negative poles and positive poles exist within the molecule (a permanent dipole).
How can a molecule contain polar bonds yet be non-polar?
The polar bonds are arranged symmetrically and so polarity cancels out.
Is water polar or non polar?
Polar
What is an experiment to distinguish polar and non-polar liquids?
- Full burette with liquid being tested.
- Charge a plastic rod.
- Open the burette and hold the charged rod close to the stream of liquid.
Stream deflects = polar liquid
Stream unaffected = non-polar liquid
What are the types of Van der Waals forces?
- LDF
- Permanent dipole - permanent dipole interactions
- Hydrogen bonding
What is an intermolecular force?
Forces between molecules.
What are LDF?
The weakest type of Van der Waals force. Occurs between all atoms and molecules.
What causes LDF?
Constantly moving electrons causing an uneven distribution of electrons and thus the formation of temporary dipoles.
True or false:
Larger atom = more electrons = stronger LDF
True
What is a pd-pdi?
The electrostatic attraction between the oppositely charged parts of a dipole of two of more polar molecules. Occurs only between polar molecules.
Is this a pd-pdi?
H—Cl- - - - -H—Cl
Yes (the dashed line)
Why do polar molecules have stronger m.p than non-polar molecules?
Pd-pdi are stronger than LDF.
What is hydrogen bonding?
A special type of pd-pdi. It exists between polar molecules that contain a Hydrogen atom directly bonded to a Fluorine, Nitrogen or Oxygen atom.
What is the strongest Van der Waals force?
Hydrogen bonding
H bonding = high m.p
True or False: Hydrogen bonding is stronger than covalent bonds.
FALSE
Is this molecule polar or non-polar?
O=O
Non-polar.
- Both oxygen so electronegativities will be the same.
- The molecule is arranged symmetrically.
What is the solubility rule?
“Like dissolves like.”
Explain “like dissolves like.”
Polar solvents will dissolve charged/polar/ionic molecules.
Non-polar solvents will dissolve non-polar solutes.
True or false: The stronger the Van der Waals forces between a liquid are, the more viscous it will be.
True
What is viscosity?
Thickness.
e.g Oil is more viscous than water.
The ____ hydrogen bonds there are, the more _____ it will be.
- more
- viscous
Order these forces from most viscous to least.
pd-pdi
H bonding
LDF
- H bonding
- pd-pdi
- LDF
(The forces themselves are not viscous but the liquid they make up will be)
What elements can be present in H bonds?
Hydrogen (necessary)
Fluorine
Oxygen
Nitrogen
Are covalent bonds Van der Waals’ forces?
No
