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An atom of potassium has atomic number 19 and mass number 39 - Edexcel - GCSE Chemistry - Question 2 - 2020 - Paper 1
Question 2
An atom of potassium has atomic number 19 and mass number 39. (i) Give the electronic configuration of this potassium atom. (ii) This potassium atom forms the ion ... show full transcript
Worked Solution & Example Answer:An atom of potassium has atomic number 19 and mass number 39 - Edexcel - GCSE Chemistry - Question 2 - 2020 - Paper 1
Step 1
Step 2
Which row shows the number of protons and the number of neutrons in this potassium ion, K⁺?
Answer
For the potassium ion K⁺, the number of protons is 19 (since the atomic number is the number of protons), and the number of neutrons can be calculated using the mass number:
Thus, we have:
Therefore, the correct row is B (19 protons and 20 neutrons).
Step 3
Explain, in terms of electrons, why potassium and caesium are in the same group.
Answer
Potassium (K) and Caesium (Cs) are both in Group 1 of the periodic table, known as the alkali metals. The reason they are in the same group relates to their electron configuration. Both elements have a single electron in their outermost shell:
- Potassium:
- Caesium:
This commonality indicates they have similar chemical properties, primarily their reactivity, as they tend to lose this single outer electron easily.
Step 4
Explain, in terms of fluorine molecules, why the boiling point of fluorine is low.
Answer
Fluorine molecules (F₂) are held together by weak Van der Waals (dispersion) forces. These forces are relatively weak compared to stronger intermolecular forces found in substances with higher boiling points. Because these weaker forces require less energy to overcome, fluorine has a low boiling point of -188 °C. Hence, at room temperature, fluorine exists as a gas.