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A calcium atom has a mass number of 40 - Edexcel - GCSE Chemistry - Question 8 - 2020 - Paper 1
Question 8
A calcium atom has a mass number of 40. (i) Which row of the table shows the number of protons and number of neutrons in this atom of calcium? (1) Explain, using ... show full transcript
Worked Solution & Example Answer:A calcium atom has a mass number of 40 - Edexcel - GCSE Chemistry - Question 8 - 2020 - Paper 1
Step 1
Which row of the table shows the number of protons and number of neutrons in this atom of calcium?
Answer
A calcium atom has 20 protons, as it is in group 2 of the periodic table. To find the number of neutrons, subtract the number of protons from the mass number:
Number of neutrons = Mass number - Number of protons = 40 - 20 = 20. Therefore, the row should show 20 protons and 20 neutrons.
Step 2
Explain, using the information in Figure 8, in which period of the periodic table calcium can be found.
Answer
Calcium is found in period 4 of the periodic table. This can be determined by noting its atomic number, which is 20, placing it in the 4th row. Additionally, elements in period 4 are characterized by having their outermost electrons in the 4th electron shell.
Step 3
Step 4
State why potassium is higher in the reactivity series and reacts more vigorously with water than calcium.
Answer
Potassium is higher in the reactivity series due to its larger atomic size and lower ionization energy compared to calcium, making it easier for potassium to lose its outer electron and react vigorously with water.
Step 5
Explain, in terms of bonding and structure, why the properties of the product, calcium chloride, are different from the properties of the reactants, calcium and chlorine.
Answer
Calcium chloride (CaCl₂) is an ionic compound formed from calcium, a metal, and chlorine, a non-metal. It has a lattice structure of alternating positive (Ca²⁺) and negative (Cl⁻) ions held together by strong electrostatic forces of attraction. This structure gives it a high melting point, as a large amount of energy is required to break these ionic bonds. In contrast, calcium is a reactive metal and chlorine is a gaseous non-metal, which exhibit different physical properties such as conductivity and state at room temperature. Furthermore, as an ionic compound, calcium chloride conducts electricity in the molten state, unlike isolated calcium and chlorine.