Flashcards · 7405 · AS Topic 1

Atomic structure (AS Level) flashcards

18 cards on AS Topic 1, subtopics 3.1.1.1 to 3.1.1.3. Pick a subtopic or study them all.

Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.

All 18 cards

For a quick read-through or printing. Cover the right-hand side to test yourself.

Relative mass and relative charge of a proton, a neutron and an electron: Proton: mass 1, charge +1. Neutron: mass 1, charge 0. Electron: mass 1/1840 (often given as 1/1836), charge −1.
Atomic number and mass number: Atomic number (proton number): the number of protons in the nucleus. Mass number: the number of protons plus neutrons.
What did Rutherford’s gold foil experiment show, and which model did it replace?: Most alpha particles passed straight through, a few were deflected and a tiny fraction bounced back. So the atom has a tiny, dense, positive nucleus and is mostly empty space. It replaced the plum pudding model.
What did Bohr and Chadwick each add to the model of the atom?: Bohr: electrons occupy fixed energy levels (shells). Chadwick (1932): the nucleus also contains neutrons, neutral particles with a mass similar to the proton.
How many protons, neutrons and electrons are in ²⁴Mg²⁺ (atomic number 12)?: 12 protons, 12 neutrons (24 − 12) and 10 electrons (two lost to give the 2+ charge).

Isotopes, and why isotopes of an element react in the same way: Atoms of the same element with different numbers of neutrons. Chemistry depends on the electron arrangement, which is the same, so their chemical properties are identical.
The five stages of time-of-flight (TOF) mass spectrometry, in order: Ionisation, acceleration, ion drift, detection, data analysis.
Electron impact vs electrospray ionisation: Electron impact: a high-energy electron knocks an electron out, forming X⁺ (elements and low-Mr compounds). Electrospray: the sample gains a proton, forming XH⁺ (large molecules that would otherwise fragment).
In TOF mass spectrometry, why do lighter ions reach the detector first?: All ions are accelerated to the same kinetic energy. Since KE = ½mv², lighter ions have a higher speed, so they cross the drift region in less time.
An electrospray spectrum shows a molecular ion peak at m/z 181. What is the Mr?: 180. Electrospray forms XH⁺, so the m/z is one more than the Mr: subtract 1.
Magnesium is 79.0% ²⁴Mg, 10.0% ²⁵Mg and 11.0% ²⁶Mg. Calculate its Ar.: (24 × 79.0 + 25 × 10.0 + 26 × 11.0) ÷ 100 = 2432 ÷ 100 = 24.3

Electron configurations of Fe and Fe²⁺: Fe: [Ar]3d⁶4s². Fe²⁺: [Ar]3d⁶. The 4s electrons are lost first, even though 4s fills before 3d.
The two Period 4 exceptions to the filling order: Cr = [Ar]3d⁵4s¹ and Cu = [Ar]3d¹⁰4s¹, because a half-filled or filled d sub-shell gives extra stability.
First ionisation energy: The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions. X(g) → X⁺(g) + e⁻
Why does first ionisation energy decrease down a group?: More shells, so a larger atomic radius and more shielding. The outer electron is held less tightly, which outweighs the increase in nuclear charge.
Why is the first ionisation energy of Al lower than that of Mg?: Aluminium’s outer electron is in a 3p sub-shell, which is higher in energy and slightly shielded by the 3s electrons, so it is easier to remove.
Why is the first ionisation energy of S lower than that of P?: Sulfur has two electrons paired in one 3p orbital, and the repulsion between them makes one easier to remove.
How do successive ionisation energies show the group of an element?: A large jump occurs when an electron is removed from a shell closer to the nucleus. The number of electrons removed before the first big jump is the number of outer electrons, which gives the group.