Video: Identifying the Family of Elements That Form Colored Ions in a Set of Element Families

Which of the following is the family of elements that form colored ions? [A] Alkali metals [B] Alkaline earth metals [C] Transition elements [D] Halogens [E] Noble gases


Video Transcript

Which of the following is the family of elements that form colored ions? (A) Alkali metals, (B) alkaline Earth metals, (C) transition elements, (D) halogens, or (E) noble gases.

This question is asking us about elements which form colorful ions. So we need to find a family of elements that form both ions and colorful ions. Let’s look at our periodic table. The alkali metals can be found in group one. Notice that we don’t tend to include hydrogen as part of the alkali metals even though it’s in group one. Examples of alkali metals are lithium, sodium, and potassium.

Let’s take a closer look at some of these examples. Sodium can form the sodium plus cation. Sodium cations can be found in something like sodium chloride, table salt. And of course table salt is not a colorful solid. Just to be sure, let’s have a look at another alkali metal, potassium. Potassium also forms one plus cations in something like potassium hydroxide, for example. Potassium hydroxide may also be called caustic potash or lye and again is a white solid, not colorful. So let’s rule out alkali metals as a correct answer.

Answer (B) the alkaline Earth metals can be found in group two. Examples of these include beryllium, magnesium, and calcium. Again, let’s take a closer look at some of these examples. Magnesium, for example, can form a two plus cation. This cation can be found in something like magnesium sulfate, MgSO4. Magnesium sulfate is commonly used in laboratories as a drying agent. So you may be familiar with it already and know that it comes as a white powder. Let’s have a look at calcium. Calcium also forms two plus cations like that in calcium carbonate, CaCO3. Calcium carbonate is the main component in lime scale, which of course is a chalky white solid. So it’s safe to assume that the alkaline Earth metals do not form colorful ions.

Let’s move on to the transition elements. The d-block in the center of the periodic table contains transition elements, sometimes called transition metals. Bear in mind that not every element in the d-block is a transition element. Common examples of transition elements are iron and copper. Let’s take a look at iron. Iron can readily form both two plus and three plus cations. Examples of iron two plus are iron two oxide, FeO, and iron two chloride, FeCl2. Iron two oxide is black, while iron two chloride is off-white. However, if you dissolve iron two chloride in solution, it becomes pale green. Now, let’s look at iron three plus. Iron three oxide, Fe2O3, is rust, so is a reddish brown color. Iron three chloride, FeCl3, is green.

We can see that iron does indeed form colorful ions. But what about another transition element? We should check to be safe. Let’s look at copper. Copper tends to form one plus or two plus cations. Copper one oxide, Cu2O, is red, while copper two oxide, CuO, is black. And of course, copper two sulfate, CuSO4, is blue. And this is a very familiar sight in the laboratory. So transition elements do form colorful ions. So this is a correct answer to the question.

Just for completeness, let’s look at the last two potential answers. Answer (D) halogens can be found on the right of the periodic table in group 17. Examples of halogens include fluorine, chlorine, and bromine. Chlorine, for example, can form a one minus anion, the chloride anion. And we’ve already come across this in NaCl, sodium chloride. Sodium chloride being table salt is of course a white solid. Just to be safe, let’s have a look at another halogen, this time fluorine. Just like chlorine, fluorine forms a one minus anion, the fluoride anion. And we tend to come across fluoride anions every day.

Fluoride anions are commonly found in toothpaste. Because we don’t want to be rubbing lots of colorful ions all over our pearly white teeth, it’s safe to assume that fluoride ions are therefore not colorful. So we can rule out the halogens as an answer. And finally, we come to the noble gases on the far right of the periodic table in group 18. Examples of noble gases are neon and argon. But do these form colorful ions? You should remember that noble gases are very stable. This makes them highly unreactive and very unlikely to form ions at all, let alone colorful ones. Because the noble gases don’t tend to form ions, we can rule this out as an answer.

So the family of elements which form colored ions are the transition elements.

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