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Question

Mg becomes Mg2+ , Se becomes Se2- How do the size ratios of atom to ion change in magnesium and selenium?

dedem · Answer

Good Morning, the magnesium cation (Mg 2+ ) is smaller than the magnesium atom (Mg). This is due to the fact that in a magnesium atom 12 electrons are driving around in the atomic shell. These 12 electrons (minus charges) are attracted by 12 protons (plus charges) in the atomic nucleus. But the electrons also keep themselves at a distance in the shell because they all have the same charge (and, as is known, equal-charged particles strike each other). Thus, on the one hand, a magnesium atom is uncharged (because the 12 additional charges in the core of the 12 minus charges in the shell are precisely compensated (repeated) in their effect. On the other hand, the 12 electrons in the shell need a certain space... In magnesium cation (Mg 2+ In contrast, 12 protons are still in the core, but only 10 electrons are in the shell. This means that the slightly fewer existing electrons are now attracted a bit more strongly by the core, because a minimally more positive charge from the core acts on each electron. At the same time, two electrons are also fewer in the shell, which leads to the remaining ten electrons no longer need so much space. Therefore, the magnesium cation is smaller in diameter than the magnesium atom (greater attraction of the core and equally fewer charge carriers in the shell). That's exactly different when it comes to selenium. A selenium atom has 34 protons in the core and 34 electrons in the shell. A Selenide anion (Se 2 ) has 34 protons in the core, but now 36 electrons in the shell. This means that the 36 electrons in the shell are only attracted by 34 protons in the core. The attraction per proton is thus somewhat smaller for the individual electrons in the selenide anion than in the selenide atom. At the same time, in the selenide anion, more equally charged particles are now bumbled in the shell than before in the atom, so that the mutual repulsion requires more space than before. For this reason, selenium atoms are smaller than selenide anions (lower attraction of the core with a greater number of equally charged electrons in the shell). All right? LG from the Waterkant