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To celebrate the 150th anniversary of the discovery of the periodic system, 2019 has been designated as the International Year of the Periodic Table of Chemical Elements by the United Nations (UN) - Leaving Cert Chemistry - Question 5 - 2016
Question 5
To celebrate the 150th anniversary of the discovery of the periodic system, 2019 has been designated as the International Year of the Periodic Table of Chemical Elem... show full transcript
Worked Solution & Example Answer:To celebrate the 150th anniversary of the discovery of the periodic system, 2019 has been designated as the International Year of the Periodic Table of Chemical Elements by the United Nations (UN) - Leaving Cert Chemistry - Question 5 - 2016
Step 1
What is meant by the periodic system in the context of Mendeleev’s 1869 periodic table of the elements?
Answer
The periodic system refers to the arrangement of elements in a tabular format where elements are listed according to their relative atomic mass and grouped based on similar chemical properties. Mendeleev’s 1869 table showcased the periodic trends observed in the properties of elements, illustrating that these properties repeat at regular intervals.
Step 2
Comment on the positioning of tellurium (Te) and iodine (I) in the 1869 table.
Answer
In Mendeleev's table, tellurium (Te) was placed before iodine (I) despite tellurium having a higher atomic mass. This was an inconsistency as Mendeleev prioritized chemical properties over atomic weight in some instances, leading to a misplacement that reflected the understanding of atomic masses at that time. He believed that their chemical properties aligned better in this order.
Step 3
Why did the 1869 table not include any noble gases?
Answer
The 1869 periodic table did not include noble gases because they had not been discovered yet. The noble gases, such as helium, neon, argon, krypton, xenon, and radon, were identified later in the 20th century due to their inert nature, and hence, Mendeleev could not account for them in his original table.
Step 4
Step 5
Give an advantage of arranging the elements in order of atomic number.
Answer
Arranging elements by atomic number simplifies the classification and predictability of element properties. It highlights periodic trends more effectively than relative atomic mass, which can lead to inconsistencies in grouping elements.
Step 6
Explain why all the elements of Group 18 in the periodic table are chemically inert.
Answer
Group 18 elements, known as noble gases, have a complete outer electron shell which leads to their lack of reactivity. This stable electronic configuration prevents them from easily forming chemical bonds with other elements.
Step 7
Explain how and why the reactivity of the halogens changes down Group 17.
Answer
The reactivity of halogens decreases down Group 17 due to the increase in atomic size and the associated increase in shielding effect. As atomic radius increases, the outermost electrons are further from the nucleus and feel a weaker electrostatic attraction, making it harder to gain additional electrons.
Step 8
How would you expect a small sample of francium to react in water?
Answer
Francium is expected to react violently with water, producing heat and releasing hydrogen gas, which may ignite. The reaction would be more explosive compared to other alkali metals due to francium's high reactivity.
Step 9