Question

Which on the following correclty ranks the atoms and ions in order of decreasing size

1. br->se2->sr2+
2.Mg>si>s
3.Sr2+>Sr+>Sr.
4.Ar>Cl>s

Answer 1

The correct decreasing order of size for the given entities is Sr2+>Sr+>Sr, reflecting the trend that cations are smaller than their neutral atoms, with more positively charged ions being smaller.

Step-by-step explanation:

The question aims to understand the ranking of different atoms and ions based on their size, which is typically dependent on their positions in the periodic table. Size typically increases as you move down a group and decreases as you move across a period from left to right. Positive ions (cations) are typically smaller than their parent atoms because they have lost one or more electrons, leading to a diminished electron cloud and a stronger attraction between the remaining electrons and the nucleus. Negative ions (anions) are usually larger than their parent atoms due to the addition of one or more electrons, which increases electron-electron repulsion in the electron cloud. Isoelectronic species have the same number of electrons, and among them, the species with more protons in the nucleus will be smaller due to the greater nuclear charge exerting a stronger pull on the electrons.

Analysis of Options

1. Br->Se2->Sr2+: This ranking is incorrect. According to periodic trends, as you go up a group, the size decreases. Therefore, Se2- should be larger than Br- because selenium is above bromine in the periodic table, and Sr2+, being a cation, should be the smallest.
2. Mg>Si>S: This ranking is also incorrect. Upon moving across a period from left to right, atomic size decreases. Therefore, S should be smaller than Si, and Si should be smaller than Mg.
3. Sr2+>Sr+>Sr: This sequence correctly reflects that cations are smaller than their neutral atoms, with more positively charged ions being smaller.
4. Ar>Cl>S: This option is incorrect because as you move across the periodic table from left to right, atoms typically decrease in size. Cl should be smaller than S, and Ar, being a noble gas with a complete valence shell, should be larger than Cl.

Therefore, the correct sequence reflecting the decrease in size would be: Sr2+>Sr+>Sr.