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Atomic force microscope image of a PTCDA molecule
An actual image of a molecule from an ultra-high resolution "atomic force microscope"

What Are Molecules?

Molecules are groups of two or more atoms, held together with chemical bonds. In other words, they are the smallest unit of a chemical compound.

Molecules come in all shapes and sizes, ranging from simple diatomic (two-atom) molecules like oxygen (O2) to complex biomolecules like DNA, which can contain many thousands of atoms. So, while there are only 118 different elements on the periodic table, there is an almost endless number of ways to combine atoms into different molecules.

The Different Types of Chemical Bonds

Chemical bonds are formed when atoms share their electrons in different ways. The way that a molecule's atoms are bonded together determines its properties and behavior, such as its shape, size, and chemical reactivity.

  • Ionic Bonds: Ionic bonding is when atoms fully transfer electrons from one atom to another. Some atoms lose electrons and become positively charged, while other atoms take these electrons and become negatively charged. These electrically charged atoms are known as ions. Like magnets, the oppositely charged ions strongly attract each other, and can form strong bonds. Ionic bonding can be found in compounds like table salt (NaCl), where a positive sodium ion (Na+) is bonded to a negative chlorine ion (Cl-).
  • Covalent Bonds: Covalent bonding is when atoms join together by sharing one or more pairs of electrons. Because the electrons are shared between atoms, covalent bonding forms a stronger connection between atoms than ionic bonding. Covalent bonds can be found in many molecules around us, like water (H2O) and carbon dioxide (CO2).
  • Metallic Bonds: Metallic bonding occurs only between metal atoms. Metals have a special feature: their outermost electron shells are only partially filled with electrons. Instead of sharing or transferring electrons, metal atoms form a sea of electrons that move freely between atoms. This is what gives metals their cool characteristics, like their ability to conduct heat and electricity.

Top Facts About Molecule for Kids

  • 1. The "world's smallest film" was created by moving around individual molecules.

    Frame from A Boy and His Atom In 2013 the computer manufacturer IBM released a stop-motion movie onto YouTube entitled, A Boy and His Atom. The movie was made by taking pictures with a scanning electron microscope, where individual molecules of carbon monoxide (CO) are magnified over 100 million times in size. The molecules were then moved around to create the images of a boy dancing and playing with an atom.

  • 2. Some molecules can store energy, like microscopic batteries.

    Adenosine triphosphate (ATP) is a molecule found in all living things, from tiny bacteria and plants to giant whales. ATP is often called the "energy currency" of cells because it's used to store energy for cellular processes, like making proteins or moving muscles.

    ATP is made up of three parts: a sugar called ribose, a nitrogen (N) molecule called adenine, and three groups of atoms containing phosphorus (P). When cells need energy, they break a bond in an ATP molecule, which turns it into ADP (adenosine diphosphate) and releases energy.

  • 3. The full name of the longest molecule found in nature would take over 3 hours to pronounce.

    Titin is a protein found in muscles, and the largest molecule found in nature. Like all other proteins, titin is a chain of many smaller molecules called amino acids. Its full chemical name has 189,819 letters, which come from combination of chemical symbols, numbers, and dashes, representing the structure and order of the amino acids in the protein.

  • 4. There's a molecule that looks like a soccer ball.

    Buckminsterfullerene is a molecule made up of 60 carbon atoms arranged in a spherical, or ball, shape. It's named after the inventor Buckminster Fuller because it kind of looks like some of his creations, called geodisk domes.

  • 5. A molecule's shape is just as important as the atoms that make it.

    Isomers are molecules that have the same chemical formula, or exact same amount and types of atoms, but with different shapes. Think of it like building with Legos. Even if you have two kits with the same exact Lego pieces, you can still use them to build different things, depending on how you arrange the pieces. Even though they have the same chemical formulas, isomers can have chemical properties that are quite different from one another.

  • 6. The largest known molecule contains millions of atoms.

    PG5 is a synthetic, or lab-made, molecule, containing about 200 million atoms. It was created by chemists at the Federal Institute of Technology in Z├╝rich. Before its creation, polystyrene, also known as styrofoam, was the largest known molecule, containing about 40 million atoms.