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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 t... 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
The number of protons in a calcium atom is 20, as calcium has an atomic number of 20. The number of neutrons can be calculated by subtracting the atomic number from the mass number:
Thus, the row should indicate 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 located in Period 4 of the periodic table. This is determined based on its electron configuration. Calcium has 20 electrons, which can be distributed in the electron shells as follows: 2 in the first shell, 8 in the second, 8 in the third, and 2 in the fourth shell. Since the highest energy level that contains electrons is the fourth shell, calcium is classified in Period 4.
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 than calcium due to its larger atomic radius and lower ionization energy, which enables it to lose its outer electron more readily. This results in potassium reacting more vigorously with water compared to calcium.
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 ( ext{CaCl}_2 ext) is an ionic compound formed from the reaction between calcium, a metal, and chlorine, a non-metal.
Structure
Calcium chloride has a crystal lattice structure which consists of positively charged calcium ions ( ext{Ca}^{2+}) and negatively charged chloride ions ( ext{Cl}^-). This structure is responsible for its solid state at room temperature.
Melting Point
The ionic bonds in calcium chloride are strong, requiring a large amount of energy to break these bonds, thus giving it a high melting point compared to both reactants.
Conductivity
In solid form, calcium chloride cannot conduct electricity because the ions are fixed in place. However, when melted or dissolved in water, the ions are free to move, allowing it to conduct electricity.
In contrast, both calcium and chlorine exist in different forms before the reaction: calcium as a metal and chlorine as a diatomic molecule (Cl2), neither of which have the properties of an ionic compound, such as high melting points or electrical conductivity when solid.