Unit 1 Flashcards
Ionisation energy
Ionisation energy (IE) is defined as the energy required to remove one mole of electrons from one mole of gaseous atoms (one electron from each atom). The units used are kilojoules per mole (kJ mol‑1)
What happens to ionisation energies as you move down a group?
Decrease because there are more electrons, shielding stops the protons from being so attracted to them. Decrease because the outer electrons are further away from the nucleus.
What happens to ionisation energies across a period?
Increase because more protons hold on tighter to the electrons to stop them leaving. When more electrons are added, the protons hold onto them tighter and the covalent radius decreases, the electrons are closer to the protons so its harder to take them away.
Covalent radius?
Half of the distance between the nuclei of two bonded atoms.
What happens to covalent radius across a period?
Decreases, because the number of protons increases and these hold onto the electrons in the shells more tightly and bring them closer.
What happens to covalent radius down a group?
Increases, because the number of electron shells increases, and the protons can’t hold onto the outer electron shells as tightly so they are further away from the nucleus.
What happens to electronegativity across a period?
Increases, because more protons means that there is an increased positive charge, so it wants more electrons.
What happens to electronegativity down a group?
Decreases, the outer electrons are further from the positive nucleus so the want for more electrons is decreased by shielding.
Bonding continuum?(Difference in electronegativities)
(Difference in electronegativities)
Under 0.4- pure covalent
Between 0.4 and 1.7- Polar covalent
Above 1.7- Ionic Bonding
which is the strongest intermolecular force
hydrogen bonding
which is the weakest kind of intermolecular forces?
london dispersion forces
Explain how the structure of the water molecules allows any attraction to occur to a charged rod. (3 marks)
Water is a polar molecule. (1 mark) A positively charged rod will cause the negative ends of the water molecules to point towards and be attracted to the positive rod. (1 mark) A negatively charged rod will cause the positive ends of the water molecules to point towards and be attracted to the negative rod. (1 mark) (Drawing a picture in an exam would be a good idea!)
discrete covalent molecules (first 20 elements)
H, F, Cl, O, N, P, S
Describe the relationship between number of electrons and boiling point and explain why it occurs (3-4 marks)
When there is a bigger molecule, there are more electrons. when there are more electrons, the london dispersion forces are greater because the dipoles are more polar. The london dispersion forces in a larger molecule with more electrons are more difficult to overcome, therefore the boiling point will be higher as it takes more energy to overcome the LDFs
What is required for a hydrogen bond to occur? What must the hydrogen atom be?
-The positive end of a strong dipole (have a big electronegativity difference with the other molecule)
-Have a small, highly electronegative atom on a neighbouring molecule.
What 3 elements are small and electronegative enough to be involved in hydrogen bonding?
F, O and N (Flourine, Oxygen and Nitrogen)
Why is solid water (ice) less dense than liquid water?
As water freezes, the intermolecular hydrogen bonding spreads out the water molecules into a strong ‘open’ structure with large spaces in it. This makes ice less dense and able to float on water.
The arrangement of water molecules in ice maximises the hydrogen bonding between them and leads to an open structure.
like dissolves like meaning
Polar solvents can generally dissolve polar substances, and ionic solids. In the same way, because the intermolecular attractions are of a similar type, non-polar solvents are more likely to dissolve non-polar substances
