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An atom of potassium has atomic number 19 and mass number 39 - Edexcel - GCSE Chemistry Combined Science - Question 5 - 2020 - Paper 1
Question 5
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 Combined Science - Question 5 - 2020 - Paper 1
Step 1
Step 2
(ii) Which row shows the number of protons and the number of neutrons in this potassium ion, K<sup>+</sup>?
Answer
In the potassium ion K<sup>+</sup>, the atom loses one electron but maintains the same number of protons. Therefore:
- Number of protons: 19
- Mass number (39): 19 protons + 20 neutrons.
- Number of neutrons: 20. Thus, the correct answer is B: 19 protons and 20 neutrons.
Step 3
(b) Explain, in terms of electrons, why potassium and caesium are in the same group.
Answer
Potassium (K) and caesium (Cs) are in the same group of the periodic table because they both have a single electron in their outermost shell. This configuration leads them to exhibit similar chemical properties, including their reactivity with other elements.
Step 4
(c) Explain, in terms of these forces, why the boiling point of fluorine is low.
Answer
Fluorine molecules experience weak forces known as Van der Waals forces (or London dispersion forces). Because these forces are relatively weak compared to other types of intermolecular forces (like hydrogen bonding or ionic interactions), less energy is required to overcome them. Consequently, fluorine has a low boiling point of -188 °C.