Determine which of the following elements would lose electrons when becoming ions:
i. hydrogen
ii. helium
iii. iron
iv. fluorine
v. gallium

The correct answer is I, III, V:

Hydrogen

Iron

Gallium

Let us take another look at the periodic table. The periodic table is composed of metals, metalloids and nonmetals.

Metals loose electrons more easily, that is why they form cations. Metals are found towards the left hand side of the periodic table.

As we move away from the left hand side of the periodic table, the ability to form cations decreases as metallic character decreases and elements become more nonmetallic.

The noble gas helium rarely looses electrons. Fluorine would rather accept an electron to form a uninegative ion.

Hence, the elements hydrogen, iron and gallium are metals hence they loose electrons more easily.

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I, III, and V  

Explanation:

All five options are correct.

However, your instructor is probably expecting the answer I, III, and V.

These three elements are on the left-hand side of the Periodic Table. Thus, they tend to lose electrons and form positive ions most easily.

H is the most reluctant to form a cation. Its first ionization energy is 1100 kJ·mol⁻¹.

However, F and He can lose electrons to form cations.

It takes only 1700 kJ·mol⁻¹ to remove an electron from F. However, F tends to add electrons to get a complete valence shell.

Even He, with a complete valence shell, will give up a valence electron for the expenditure of only 2400 kJ·mol⁻¹.