atomic structure QP

Question 1

A sample of rubidium contains the isotopes 85Rb and 87Rb only.
The isotope 85Rb has an abundance 2.5 times greater than that of 87Rb
Calculate the relative atomic mass of rubidium in this sample.
Give your answer to one decimal place.

Answer 1

(85 × 2.5) + 87 ×1
————————-
3.5

= 85.6

Question 2

By reference to the relevant part of the mass spectrometer, explain how the abundance of an isotope in a sample of rubidium is determined.
Name of relevant part
explanation

Answer 2

detector

Current / electrical signal (NOT charge) proportional to abundance

Question 3

Predict whether an atom of 88Sr will have an atomic radius that is larger than, smaller than or the same as the atomic radius of 87Rb. Explain your answer.
Atomic radius of 88Sr compared to 87Rb

explanation

Answer 3

smaller

Bigger nuclear charge / more protons in Sr Same shielding

Question 4

Give one reason why the second ionisation energy of silicon is lower than the second ionisation energy of aluminium.

Answer 4

Electron in Si removed from 3p orbital/sub-shell, which is higher energy than electron removed from 3s orbital/sub-shell in Al

Question 5

Predict the element in Period 3 that has the highest second ionisation energy.
Give a reason for your answer.
Element
reason

Answer 5

sodium

Electron (removed) from the 2nd shell / 2p orbital

Question 6

Explain why the ionisation energy of every element is endothermic.

Answer 6

Heat or energy needed to overcome the attraction between the (negative) electron and the (positive) nucleus or protons