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Consider the data given in the table about the elements chlorine, argon and potassium - Leaving Cert Chemistry - Question 5 - 2021
Question 5
Consider the data given in the table about the elements chlorine, argon and potassium. | Element | Year discovered | First ionisation energy (kJ mol⁻¹) | Second ion... show full transcript
Worked Solution & Example Answer:Consider the data given in the table about the elements chlorine, argon and potassium - Leaving Cert Chemistry - Question 5 - 2021
Step 1
How did Mendeleev arrange the elements in his periodic table of 1869?
Answer
Mendeleev arranged the elements according to increasing atomic weight (atomic mass). He also grouped elements with similar properties into vertical columns (groups). This arrangement allowed for the observation of periodic trends, as the properties of the elements varied periodically.
Step 2
Suggest a reason why Mendeleev did not suspect the existence of argon.
Answer
Mendeleev did not suspect the existence of argon because noble gases were unknown at the time and were not included in his first periodic table. Additionally, the inertness and unreactivity associated with noble gases contributed to the lack of suspicion regarding their existence. There were no gaps indicating a missing element at that time.
Step 3
How do we know that any new elements discovered in the future will be ‘super-heavy’; i.e., elements that have very large relative atomic masses?
Answer
There are no gaps in the modern periodic table. All known elements up to around atomic number 117 (118 known) have been discovered, and the elements that fall beyond this are anticipated to be heavier. The trend in atomic mass increases with atomic number, indicating that any future discoveries will likely involve heavier elements with substantially larger atomic masses.