Structure and bonding Flashcards
What is electronegativity?
The ability of an atom to attract electrons towards itself in a covalent bond
The further up and right you go in the periodic table, the more…
Electronegative an element is
What is the most electronegative element on the periodic table?
Fluorine
What scale helps to identify how electronegative an element is?
The Pauling Scale
If there’s a big difference in electronegativity in a compound, what does this mean?
The compound will be more ionic and the bond will be more polar
If there’s an electronegative difference of 0, what does this tell us about the molecule?
That it’s mostly covalent
What’s an example of a mostly covalent molecule?
Cl2
Are hydrocarbons polar or non polar?
Non polar
Why is carbon dioxide non polar?
Because the polar bonds are arranged symmetrically and so overall there’s no polarity
What is the strongest intermolecular force?
Hydrogen bonds
What is the weakest intermolecular force?
London forces
What molecules or atoms do London forces exist in?
All molecules and atoms with electrons
Are more London forces existent in molecules/atoms that are bigger?
Yes because larger molecules/atoms have more electrons
Which hydrocarbons have more London forces?
Longer, straight chained hydrocarbons
Why do branched hydrocarbons have less London forces?
Because they can’t pack together as close
What atoms/molecules are permanent dipole-dipole interactions existent in?
Atoms/ molecules with a polarity
Which has weaker London forces, alkanes or alcohols?
Alkanes
Do halides have permanent dipoles?
Yes
What are the 3 most electronegative elements on the periodic table?
Nitrogen, oxygen, and fluorine
What needs to be present for hydrogen bonding to occur?
Hydrogen bonded to a strongly electronegative element and at least 1 lone pair of electrons
What must happen in order for a substance to dissolve?
The substance’s bonds must break, the solvent’s bonds must break, and new bonds must form between the substance and the solvent.
Do alcohols dissolve in polar solvents?
Yes, because they can hydrogen bond with water molecules.
Why can’t the hydrocarbon part of an alcohol dissolve in water?
Because the hydrocarbon part is non polar and so doesn’t dissolve in water
How does the size of an alcohol affect its solubility?
The bigger the hydrocarbon part, the less soluble the alcohol is
Why do some polar molecules, like haloalkanes, not dissolve in water?
Because their dipoles aren’t very strong and water molecules can form stronger hydrogen bonds with each other.
What type of solvents can haloalkanes dissolve in?
Solvents that interact via permanent dipole-dipole interactions
Are alkanes polar or non polar?
They’re non polar and they dissolve best in non polar solvents as they can form London forces between the molecules
What is the polarising power as applied to cations?
The ability of a cation to change the shape of an electron cloud around an anion
What is the strongest intermolecular force in methane?
London forces
What’s the strongest intermolecular force in Hydrogen Fluoride?
Hydrogen bonding
If the bond polarities don’t cancel then a molecule is what?
Polar
How can you distinguish between solid lithium chloride and solid sodium chloride?
-Put nichrome wire in solid and place in hot/blue flame
-The lithium salt should give a chrimson colour
-The sodium salt should give a yellow colour
What are London forces or Van Der Waals forces caused by?
They’re caused by the asymmetry of the electron cloud, hence causing attractive forces between neighbouring dipoles
