DP Chemistry (first assessment 2025)

Question 21N.2.HL.TZ0.9

Date	November 2021	Marks available	[Maximum mark: 8]	Reference code	21N.2.HL.TZ0.9
Level	HL	Paper	2	Time zone	TZ0
Command term	Explain, Sketch, State, Suggest	Question number	9	Adapted from	N/A

[Maximum mark: 8]

21N.2.HL.TZ0.9

Fast moving helium nuclei (⁴He²⁺) were fired at a thin piece of gold foil with most passing undeflected but a few deviating largely from their path. The diagram illustrates this historic experiment.

Figure from PPLATO / FLAP (Flexible Learning Approach To Physics), http://www.met.reading.ac.uk/pplato2/h-flap/
phys8_1.html#top 1996 The Open University and The University of Reading.

(a)

Suggest what can be concluded about the gold atom from this experiment.

[2]

Markscheme

Most ⁴He²⁺ passing straight through:

most of the atom is empty space
OR
the space between nuclei is much larger than ⁴He²⁺ particles
OR
nucleus/centre is «very» small «compared to the size of the atom» ✔

Very few ⁴He²⁺ deviating largely from their path:

nucleus/centre is positive «and repels ⁴He²⁺ particles»
OR
nucleus/centre is «more» dense/heavy «than ⁴He²⁺ particles and deflects them»
OR
nucleus/centre is «very» small «compared to the size of the atom» ✔

Do not accept the same reason for both M1 and M2.

Accept “most of the atom is an electron cloud” for M1.

Do not accept only “nucleus repels ⁴He²⁺ particles” for M2.

(b(i))

Subsequent experiments showed electrons existing in energy levels occupying various orbital shapes.

Sketch diagrams of 1s, 2s and 2p.

[2]

Markscheme

1s AND 2s as spheres ✔

one or more 2p orbital(s) as figure(s) of 8 shape(s) of any orientation (p_x, p_y p_z) ✔

(b(ii))

State the electron configuration of copper.

[1]

Markscheme

1s²2s²2p⁶3s²3p⁶4s¹3d¹⁰
OR
[Ar] 4s¹3d¹⁰ ✔

Accept configuration with 3d before 4s.

(b(iii))

Copper is a transition metal that forms different coloured complexes. A complex [Cu(H₂O)₆]²⁺(aq) changes colour when excess Cl⁻(aq) is added.

Explain the cause of this colour change, using sections 3 and 15 from the data booklet.

[3]

Markscheme

chloride is lower in the spectrochemical series ✔

«ligand cause» decreased/lesser splitting «in d-orbitals compared to H₂O» ✔

frequency/energy of light absorbed is decreased
OR
wavelength of light absorbed is increased ✔

Accept ·chloride a weaker ligand than water/produces a smaller energy difference than water for M1.

Award [2 max] for mentioning splitting of orbitals is changed AND frequency/ wavelength/energy of light absorbed
are different/changed without mentioning correct decrease or increase.

Syllabus sections

Structure 1. Models of the particulate nature of matter » Structure 1.2—The nuclear atom » Structure 1.2.1 - Atoms and negatively charged electrons. Atoms contain a positively charged, dense nucleus composed of protons and neutrons (nucleons). Negatively charged electrons occupy the space outside the nucleus. Use the nuclear symbol ZXA to deduce the number of protons, neutrons and electrons in atoms and ions.

Structure 1. Models of the particulate nature of matter » Structure 1.3—Electron configurations » Structure 1.3.4—Detailed model of the atom. A more detailed model of the atom describes the division of the main energy level into s, p, d and f sublevels of successively higher energies. Recognize the shape and orientation of an s atomic orbital and the three p atomic orbitals.

Structure 1. Models of the particulate nature of matter » Structure 1.3—Electron configurations » Structure 1.3.5—Each orbital has a defined energy state for a given electron configuration and chemical environment, and can hold two electrons of opposite spin. Sublevels contain a fixed number of orbitals, regions of space where there is a high probability of finding an electron. Apply the Aufbau principle, Hund’s rule and the Pauli exclusion principle to deduce electron configurations for atoms and ions up to Z = 36.

Question 21N.2.HL.TZ0.9

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