A Review of Elements, Compounds, and Molecules

Peter M. Williams, Elizabeth Friedl
  • Author
    Peter M. Williams

    Peter holds a Bachelor's degree in Microbiology and Biotechnology, and a Master's degree in Applied Microbiology. In addition, Peter has more than two years of experience in tutoring and writing academic materials for senior and junior schools, mainly in Sciences, Languages, and Humanities.

  • Instructor
    Elizabeth Friedl

    Elizabeth, a Licensed Massage Therapist, has a Master's in Zoology from North Carolina State, one in GIS from Florida State University, and a Bachelor's in Biology from Eastern Michigan University. She has taught college level Physical Science and Biology.

Learn about elements, compounds, and molecules, and the difference between molecules and compounds. Understand how elements and the number of atoms relate to molecules and compounds. Updated: 09/26/2021

What are Elements?

An atom is the simplest particle involved in a chemical reaction. An atom has the potential to maintain its chemical properties when subjected to physical and chemical changes. The atoms are the basic units or the building blocks of elements. Therefore, an element is a pure substance made of atoms of only one kind. Elements occur naturally, with 118 elements included in the periodic table, starting from the first element, hydrogen (H), to the last element, oganesson (Og). Elements are represented using letters and symbols, either as a single capital letter, e.g., Hydrogen (H), or a capital and a small letter, e.g., Copper (Cu).

It should be noted that all atoms of the same elements have the same number of protons, which is also referred to as the atomic number. This number is used in the grouping of elements in a periodic table.

Have you ever heard of Dmitri Mendeleev? He is recognized as the father of the periodic table. Therefore, a periodic table can be defined as a table consisting of all the chemical elements, where elements are arranged according to their physical and chemical properties.

Examples of Elements

Elements can exist as atoms, a common trait in noble gases such as helium (He), or as molecules, where two atoms have chemically bonded, e.g., oxygen (O2). Each element has its distinctive properties. Therefore, elements with the same physical and chemical properties are usually grouped in a periodic table. The position of an element in the periodic table is dictated by the number of protons it has. Precisely, the arrangement starts with elements with the least number of protons to elements with a higher number of protons.

A periodic table consists of rows and columns. The rows are known as periods, and the chemical properties of elements change as you move from left to right. For example, the number of electrons in the outer shell also increases from left to right. However, elements in the same period have the same number of energy levels.

The columns are referred to as groups that move from top to bottom. The number of energy levels increases down the group. The electrons in the outer shell remain the same in elements of the same group. Traditionally, a periodic table has four groups, namely:

  • Group 1: Alkali metals
  • Group 2: Alkaline earth metals
  • Transition metals: positioned in the middle of the table
  • Group 17: Halogens
  • Group 18 : Noble gases.

A Periodic Table

Some elements examples and their respective chemical symbols include:

  • Oxygen (O)
  • Sodium (Na)
  • Potassium (K)
  • Iron (Fe)
  • Hydrogen (H)
  • Lithium (Li)
  • Chlorine (Cl)

What Are Elements?

I was in the jewelry store the other day looking at all the different bracelets, earrings, necklaces, and rings. Some pieces of jewelry were simple: a gold ring, a platinum bracelet, a pair of silver cufflinks. Others were more complex: ruby and emerald necklaces, diamond tennis bracelets, and jade rings. This got me thinking about the periodic table because I know I can find gold, silver, and platinum on it. But try as I might, I won't find ruby, emerald, or jade on there.

What really struck me is that on the periodic table I also find things like helium, oxygen, sodium, and lead. These don't seem to have any relation to the gold, silver, and platinum, but in fact, they have something very important in common. They are all elements! An element is a material that is made of only one type of atom. This is why those beautiful gemstones in the jewelry store have no business on the periodic table - they are composites of multiple elements.

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What are Molecules?

Atoms tend to join with other atoms through chemical bonds to enhance their stability. When two atoms bond together, they form molecules. Thus, molecules are a group of atoms that have been held together by chemical bonds. These bonds can either be covalent, ionic bonds, or intramolecular forces.

Atoms form molecules by sharing electrons, e.g., in the formation of simple molecules such as oxygen. However, atoms also form molecules by either gaining or losing electrons which leads to the formation of ions. In such a case, the metal loses electrons while non-metals gain electrons.

Molecules can be made up of either one or more chemical elements. For example, an oxygen molecule comprises two atoms of the same element, thus a homonuclear molecule. On the other hand, the water molecule has three atoms where two atoms are from one element (hydrogen) and one from another element (Oxygen), thus is a heteronuclear molecule.

Molecules can also be categorized based on the number of atoms from which they are made. For instance, Helium (He) has one atom of the same element, thus a monoatomic molecule. A molecule can also have two atoms of the same or different elements, such as Oxygen gas(O2); thus, they are called diatomic molecules. In addition, molecules such as water (H20) consist of three atoms, thus known as triatomic molecules. Tetratomic molecules such as phosphorous (P4) have four atoms. Pentatomic molecules consist of five atoms, and finally, hexatomic molecules consist of six atoms.

Examples of Molecules

Molecules can either be simple molecules, made up of few atoms held by covalent bonds, or complex molecules, formed when simple molecules combine to form short or long molecules.

Examples of molecules include:

  • An oxygen molecule (O2) is a simple molecule made up of one element; oxygen. Two atoms of oxygen make this molecule.
  • A water molecule (H2O) is a simple molecule made up of two elements: hydrogen and oxygen. It consists of two atoms of hydrogen and one atom of oxygen.
  • Ammonia (NH3) is a simple molecule made up of two elements: Nitrogen and Hydrogen. It contains one atom of nitrogen and three atoms of hydrogen.
  • Hydrogen (H2)- This is a simple molecule made up of one element: Hydrogen. Two atoms of hydrogen make this molecule.
  • Vitamin C/ Ascorbic acid (C6H8C6)- This is a complex molecule, which is very common in our diet, and it is made up of two elements including carbon and hydrogen. It contains 12 atoms of carbon and eight atoms of hydrogen.
  • Phenylalanine (C9H11NO2) is an amino acid and a complex molecule made up of four elements. It contains nine carbon atoms, 11 hydrogen atoms, one nitrogen atom, and two oxygen atoms.

Phenyalanine

Molecules Are Groups of Atoms

While many things in nature do come in their pure elemental form, there are of course many other things that do not. Instead, they are combinations of elements. When elements combine, they form molecules. A molecule is a group of two or more atoms chemically bonded together.

Molecules may be simple or they may be quite complex. For example, some simple molecules include the oxygen you breathe, which is made of two oxygen atoms, the salt you put on your food, which is made of one sodium atom and one chlorine atom, or the water you drink, which is made of two hydrogen atoms and one oxygen atom. A more complex molecule would be something like glucose, which is a sugar that has numerous carbon, hydrogen, and oxygen atoms bonded together.

What isn't a molecule, then? Well, this would be any single atom of any element. Basically, if it's not paired up with at least one other atom, it's not a molecule. Molecules follow the buddy system!

Compounds Are Different Elements

Molecules are groups of two or more atoms, but there is a special sub-group of molecules, too. These are compounds, and a compound is a group of two or more different atoms chemically bonded together. The key here is that compounds are made of at least two different elements. So, this would include your water, because it's made of both hydrogen and oxygen, as well as your salt, since this is made of both sodium and chlorine.

However, the oxygen you breathe is not a compound because it contains only oxygen. But it is still a molecule because it's a combination of at least two atoms. This can be a bit confusing, because all compounds are molecules, but not all molecules are compounds. Let's look at a few more examples to see how this works.

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Video Transcript

What Are Elements?

I was in the jewelry store the other day looking at all the different bracelets, earrings, necklaces, and rings. Some pieces of jewelry were simple: a gold ring, a platinum bracelet, a pair of silver cufflinks. Others were more complex: ruby and emerald necklaces, diamond tennis bracelets, and jade rings. This got me thinking about the periodic table because I know I can find gold, silver, and platinum on it. But try as I might, I won't find ruby, emerald, or jade on there.

What really struck me is that on the periodic table I also find things like helium, oxygen, sodium, and lead. These don't seem to have any relation to the gold, silver, and platinum, but in fact, they have something very important in common. They are all elements! An element is a material that is made of only one type of atom. This is why those beautiful gemstones in the jewelry store have no business on the periodic table - they are composites of multiple elements.

Molecules Are Groups of Atoms

While many things in nature do come in their pure elemental form, there are of course many other things that do not. Instead, they are combinations of elements. When elements combine, they form molecules. A molecule is a group of two or more atoms chemically bonded together.

Molecules may be simple or they may be quite complex. For example, some simple molecules include the oxygen you breathe, which is made of two oxygen atoms, the salt you put on your food, which is made of one sodium atom and one chlorine atom, or the water you drink, which is made of two hydrogen atoms and one oxygen atom. A more complex molecule would be something like glucose, which is a sugar that has numerous carbon, hydrogen, and oxygen atoms bonded together.

What isn't a molecule, then? Well, this would be any single atom of any element. Basically, if it's not paired up with at least one other atom, it's not a molecule. Molecules follow the buddy system!

Compounds Are Different Elements

Molecules are groups of two or more atoms, but there is a special sub-group of molecules, too. These are compounds, and a compound is a group of two or more different atoms chemically bonded together. The key here is that compounds are made of at least two different elements. So, this would include your water, because it's made of both hydrogen and oxygen, as well as your salt, since this is made of both sodium and chlorine.

However, the oxygen you breathe is not a compound because it contains only oxygen. But it is still a molecule because it's a combination of at least two atoms. This can be a bit confusing, because all compounds are molecules, but not all molecules are compounds. Let's look at a few more examples to see how this works.

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