Periodic Table: Elemental Forms: Videos & Practice Problems

Elements in their natural state can be categorized based on the number of atoms they contain. Monoatomic elements, such as lithium, magnesium, and zinc, are singular atoms that are stable by themselves. Diatomic elements, which can be remembered by the mnemonic "have no fear of ice cold beer," include hydrogen ($H_2$), nitrogen ($N_2$), oxygen ($O_2$), fluorine ($F_2$), chlorine (${\mathrm{Cl}}_2$), bromine (${\mathrm{Br}}_2$), and iodine ($I_2$), and are stable as pairs. Polyatomic elements like phosphorus ($P_4$), sulfur ($S_8$), and selenium (${\mathrm{Se}}_8$) are stable in groups larger than two. These elements can further be classified as homonuclear if they are composed of identical atoms, such as $H_2$, ${\mathrm{Cl}}_2$, $P_4$, and $S_8$, or heteronuclear if they consist of different atoms, like water ($H_{2}O$), carbon dioxide (${\mathrm{CO}}_2$), ammonia (${\mathrm{NH}}_3$), and glucose ($C_6{H}_{12}{O}_6$). Understanding the stability and composition of these elements is fundamental in chemistry, as it influences their chemical properties and reactions.

Elemental Forms of Elements

Now the elements of the periodic table can exist in different forms in the natural world. Here we can say that elements exist in their most stable state when they are monoatomic elements, diatomic elements or polyatomic elements. When we say the term monoatomic elements, these are the elements that are stable alone when found in nature, because mono means one.

So if we take a look here at the periodic table, lithium, we could say magnesium, we could say zinc. None of them are shaded red or blue, so they all exist in their most stable state as monoatomic elements. So you'd find lithium by itself, magnesium by itself, zinc by itself. Other elements on the periodic table are most stable and found in a diatomic structure. So these diatomic elements, these are the elements that are stable as pairs when found in nature. Because dye means two.

To help us remember the diatomic elements, just remember have No Fear of ice cold beer. So here this would be H2 N2 F2 O2. Ice is I2. Now this C here is not carbon, it's chlorine. So that's Cl2. And B here is not boron but bromine, so this is Br2. So these are your diatomic elements of the periodic table. So hydrogen exists as a diatomic nitrogen, oxygen, fluorine, chlorine, bromine and iodine.

Now finally, some elements. In their most stable state in nature, they exist as polyatomic elements. These are elements that are stable in numbers greater than two because Poly means many. On our periodic table, we see that our polyatomic elements are Phosphorus, sulfur, and selenium. Phosphorus in nature exists as P4, Sulfur exists as S8. And remember we said that elements in the same group or column tend to have similar chemical properties because sulfur is S8. Selenium would also have 8:00 because they're in the same group, so Selenium would be Se8.

So these are the most natural forms of the elements when we look at them in nature. So just remember that we have monoatomic, diatomic and polyatomic elements.

Chalcogen Identification Example

So In this example question it says which of the following choices represents A monoatomic element that is also a chalkagen. Remember some groups have unique names. Achalcogen is from group 6A or what we know as group 16. So if we come up here, groups 6A or group 16, which is the same thing, would be this column.

Here oxygen, sulfur and selenium are automatically out because none of them are monoatomic. The monoatomic elements from this group would be Te, Po or Lv. If we look, A couldn't be our answer because it's monoatomic, but it is not a chalka jet. Sulfur is a chalcogen because it's in that group 6A, but it is polyatomic. Te is one of the three that we name.

So what's our answer? Chlorine is not a chalk Cogen. It's in Group 7/8, so it's a halogen. Also it's diatomic. Then finally, lithium. Lithium is monoatomic, yes, but it is an alkali metal and not a chalk gene. It's in Group 1A. So out of all our choices, only option C is the correct answer here.

Homonuclear vs. Heteronuclear Compounds

Sometimes we can refer to multiple elements together as being either homonuclear or heteronuclear. In homonuclear compounds, these are compounds composed of identical elements. So this would represent our diatomic and polyatomic elements. So we talk about H2, Cl2, P4, S8. These would be our homonuclear elements, or we can name them diatomic elements or polyatomic elements.

In heteronuclear compounds, this is when our compounds are composed of different elements. So a good example would be water, which is H2O, carbon dioxide, which is CO2. Ammonia gas is big with fertilizers, that's NH3. Also glucose, which we've talked about in the past, C6H12O6.

So just remember, elements can exist as either monoatomic, diatomic, or polyatomic elements, and then we can also refer to them as either homonuclear if all the elements are the same or heteronuclear if the elements together are different.

Which of the following is a homonuclear polyatomic element?

• A. Chlorine
• B. Oxygen
• C. Hydrogen
• D. Iron
• E. Selenium

Answer: (E)

Here’s what students ask on this topic:

What are diatomic elements?

Diatomic elements are a specific class of molecules consisting of two atoms of the same element bonded together. These elements naturally occur as diatomic molecules when they are in their most stable form at Standard Temperature and Pressure (STP). There are seven diatomic elements that you should be familiar with, often remembered by the mnemonic "BrINClHOF," which stands for Bromine (Br), Iodine (I), Nitrogen (N), Chlorine (Cl), Hydrogen (H), Oxygen (O), and Fluorine (F).

These elements are unique because they form diatomic molecules rather than existing as single atoms or forming compounds with different elements. For example, oxygen in the atmosphere is found as O₂, not as individual O atoms, because it is more stable as a diatomic molecule. This stability arises from the sharing of electrons between the two atoms, creating a covalent bond that holds the molecule together. Understanding diatomic elements is crucial in chemistry, as they play a vital role in various chemical reactions and processes.

How can one remember diatomic elements?

Remembering diatomic elements can be made easier with the help of a mnemonic device. A popular mnemonic for the seven most common diatomic elements is "Have No Fear Of Ice Cold Beer," which stands for Hydrogen ($H_2$), Nitrogen ($N_2$), Fluorine ($F_2$), Oxygen ($O_2$), Iodine ($I_2$), Chlorine (${\mathrm{Cl}}_2$), and Bromine (${\mathrm{Br}}_2$). Each of these elements naturally occurs as a molecule consisting of two atoms when found in their elemental form.

To further reinforce your memory, you can visualize each element or associate it with a particular image or experience. For example, imagine a pair of oxygen molecules as two friends breathing the cold air on a winter day, or picture two chlorine atoms swimming together in a pool. Associating these elements with vivid images can help cement them in your memory. Regularly revisiting and quizzing yourself on these elements can also greatly improve retention.

What are the diatomic elements?

Diatomic elements are molecules composed of only two atoms, of the same or different chemical elements. The prefix "di-" means two, indicating that these molecules are simply two atoms bonded together. There are seven elements that naturally occur as diatomic molecules in their elemental form at standard temperature and pressure (STP), and they are often referred to as the "diatomic elements." These elements are:

• Hydrogen (H₂)
• Nitrogen (N₂)
• Oxygen (O₂)
• Fluorine (F₂)
• Chlorine (Cl₂)
• Bromine (Br₂)
• Iodine (I₂)

These seven diatomic elements are all nonmetals, and they form diatomic molecules because they are more stable as pairs of atoms than as single atoms. This molecular formation is due to the elements' desire to fill their outer electron shells according to the octet rule, which makes them more chemically stable. For example, two oxygen atoms will share two pairs of electrons, forming a double bond and creating an O₂ molecule.