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
Give the electronic configuration of this potassium atom.
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Answer
The electronic configuration of potassium (atomic number 19) is given as follows:
2.8.8.1
This shows that potassium has two electrons in its first shell, eight in its second, eight in its third, and one in its outermost shell.
Step 2
This potassium atom forms the ion K<sup>+</sup>. Which row shows the number of protons and the number of neutrons in this potassium ion, K<sup>+</sup>?
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Answer
For the potassium ion K<sup>+</sup>:
Protons: 19
Neutrons: 20
Thus, 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.
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Answer
Potassium and caesium are in the same group of the periodic table because they both have the same number of electrons in their outermost shell. Specifically, both elements have one electron in their outer shell, which defines their similar chemical properties and reactivity.
Step 4
Explain, in terms of fluorine molecules.
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Answer
Fluorine boils at -188 °C due to the presence of weak intermolecular forces, specifically Van der Waals forces, between fluorine molecules (F<sub>2</sub>). These forces are relatively weak, requiring only a low temperature to overcome and change the state from gas to liquid.
