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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
Give the electronic configuration of this potassium atom
Answer
The electronic configuration of potassium (K) with atomic number 19 is given by the distribution of electrons in its atomic orbitals. It can be represented as:
This indicates that there are 2 electrons in the first shell, 8 in the second, 8 in the third, and 1 in the outermost shell.
Step 2
Which row shows the number of protons and the number of neutrons in this potassium ion, K⁺?
Answer
In a potassium ion (K⁺), the number of protons remains the same as in the neutral atom, which is 19. The mass number of potassium is 39, so the number of neutrons can be calculated as:
Thus, the correct row is B:
- Number of protons: 19
- Number of neutrons: 20
Step 3
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 the same number of electrons in their outermost shell. For both elements, this is one electron, which makes them both alkali metals. This similar electron configuration leads to similar chemical properties, including their reactivity.
Step 4
Explain, in terms of these forces, why the boiling point of fluorine is low.
Answer
The boiling point of fluorine is low due to the weak intermolecular forces present between fluorine molecules, which are London dispersion forces. These are relatively weak compared to other intermolecular forces such as hydrogen bonds or ionic bonds. As a result, only a small amount of energy is required to overcome these forces, allowing fluorine to boil at a low temperature of -188°C.