Bonding And Structure Flashcards

Question

What are London forces?

Answer 1

- cause all atoms and molecules to be attracted to each other - electrons in charge clouds move really quickly, at any particular moment, electrons in an atom are likely to be more on one side than the other. At this moment, atom would have a temporary dipole - this dipole can induce another temporary dipole in the opposite direction on a neighbouring atom. The two dipoles are then attracted to each other. This can become a domino effect. - electrons are constantly moving, the dipoles are being created and destroyed all the time. Overall, the atoms are attracted to each other - larger molecules have larger electron clouds, meaning stronger London forces - molecules with a larger surface area have a higher exposed electron cloud, so have stronger London forces

Answer 2

- The δ- and δ+ charges on molecules can cause weak electrostatic forces of attractions between molecules, e.g. hydrogen chloride gas. - Permanent dipole permanent dipole bonds happen as well as London forces not instead. - So molecules that have both London forces and permanent dipole permanent dipole forces generally have higher boiling and melting points than those with similar London forces but no permanent dipole permanent dipole forces.

Answer 3

- Covalent bonding only happens when hydrogen is covalently bonded to nitrogen, oxygen or fluorine. - nitrogen, oxygen and fluorine are very electronegative, so draw the bondong electrons away from the hydrogen atom. - the bond is so polarised, and hydrogen has such a high charge density because its so small, that hydrogen forms weak bonds with lone pairs of electrons from nitrogen, fluorine or oxygen atoms of other molecules. - examples include: water, ammonia and hydrogen fluoride - organic molecules that often form hydrogen bonds include alcohols and amine groups (-OH, -NH) - substances that form hydrogen bonds are also soluble in water, because they can form hydrogen bonds with the water

Answer 4

- ice is an example of a simple molecular structure - in ice, the water molecules are arranged so that there is the maximum number of hydrogen bonds - the lattice structure formed this way wastes lots of space - as the ice melts , some of the hydrogen bonds are broken and the lattice breaks down, allowing molecules to fill the spaces - this effect means ice is much less dense than water - which is why ice floats

Answer 5

1. Bonds in the substance have to break 2. Bonds in the solvent have to break 3. New bonds have to form between the substance and the solvent

Answer 6

- made of polar molecules, such as water. Water molecules bond to each other with hydrogen bonds. Not all polar solvents form hydrogen bonds. E.g. propanone only forms London forces and permanent dipole permanent dipole forces

Answer 7

Are made of molecules that are not polar. E.g. hexane, bond to each other through London forces

Answer 8

- When an ionic substances mix in water, the ions in the ionic substance are attracted to the oppositely charged ends of the water molecules, the ions are pulled away from the ionic lattice and the water molecules surround the ions, this is called hydration. Some ionic substances don’t dissolve because their ionic bonds are too strong

Answer 9

- they contain polar bonds but their dipoles aren’t strong enough to form hydrogen bonds with water - the hydrogen bonding between water molecules is stronger than the bonds that would be formed with halogenoalkanes, so halogenoalkanes don’t dissolve - but halogenoalkanes can form permanent dipole permanent dipole bonds, and can dissolve in polar solvents tha form permanent dipole permanent dipole bonds