Imagine a world without bonding - without chemical bonding, to be precise. Atoms ignore each other and instead just drift around in empty space, minding their own business. The water in the oceans splits into hydrogen and oxygen gases, which expand to 1500 times their liquid volume. Chlorine atoms from salts dissolved in the water form a toxic cloud, poisoning all of life with deadly fumes. Not that there is any life, or water, or in fact much of anything at all. 

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Bonding Bonding

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Table of contents

    All the reactions that take place and all the molecules that we find in life only exist because of bonding. The only elements we commonly find without bonds are noble gases.

    Bonding is the interaction of different atoms to form compounds, molecules, ions, crystals, and all the other substances that make up the world. It is caused by the lasting attraction between positive and negative charges.

    There are two categories of bonding, known as primary and secondary bonding. Primary bonding is what most people think of when the word is mentioned. Primary bonds are also known as intramolecular forces. They take place between atoms within the molecule. They’re generally strong and hard to break.

    In contrast, secondary bonds are a lot weaker. They are more commonly known as Intermolecular Forces, since they take place between molecules. When we mention bonding here, we mean primary bonding, unless otherwise stated.

    Why do bonds form?

    Atoms want to be stable - they like being in the lowest energy state possible. By combining with other atoms in various combinations, they can form different substances with much lower energy states.

    Stability depends on how many electrons an atom has in its outer shell. To be at its most stable, an atom wants to have a full outer shell of electrons, much like that of a noble gas. This is why noble gases don’t readily form bonds with other atoms. They are already as stable as they can be! Instead, we find them as monatomic gases.

    Monatomic substances consist of just one atom. Instead of bonding with another atom, each atom floats around in space by itself.

    Atoms bonded together form molecules or compounds.

    A molecule is made of two or more atoms chemically bonded together. If these atoms come from two or more different elements, then we call the molecule a compound.

    Types of bonding

    We mentioned above that bonding occurs because of attraction between positive and negative charges. You should know from Atomic Structure and Fundamental Particles that atoms are made up of protons, neutrons, and electrons. The table below summarises their charges and locations within the atom.

    Bonding, proton neutron electron comparison, StudySmarterFig. 1 - A table comparing protons, neutrons and electrons

    You can see that protons have a positive charge and electrons have a negative charge. These are the only charged particles within an atom. All attraction, and therefore all bonding, must be between protons and electrons.

    We know that atoms try to form bonds in order to achieve a full outer shell of electrons. They do this by moving their electrons around between each other. They can do this in three different ways, which result in three different types of bonding:

    • Sharing electrons results in covalent bonding.
    • Donating electrons results in ionic bonding.
    • Delocalising electrons results in metallic bonding.

    Covalent bonding

    Covalently bonded atoms share electrons with each other so that they all have full outer shells of electrons.

    A covalent bond is a shared pair of electrons.

    Only non-metals form covalent bonds. Electron orbitals from two different atoms overlap, and a shared electron pair is formed using an electron from each atom. The bond is held together by the attraction between the negative shared electron pair and the positive nuclei inside the two atoms.

    Bonding, covalent bonding example using Methane, StudySmarterFig. 2 - A diagram showing covalent bonding. Each bond contains one electron from carbon and one electron from hydrogen

    Ionic bonding

    Ionic bonding occurs between metals and non-metals. Ionic bonds are formed when a metal atom donates electrons to a non-metal. This forms charged atoms known as ions, which are attracted to each other. An ionic bond is an electrostatic attraction between oppositely charged ions.

    Bonding, ionic bonding example using sodium chloride, StudySmarterFig. 3 - A diagram showing ionic bonding. Each sodium atom donates an electron to a chlorine atom, forming positive sodium ions and negative chloride ions

    Metallic bonding

    For a metal on its own to have a full outer electron shell, it must do something quite different. Its outer electrons delocalise and the metal forms positive metal ions. Unlike in ionic bonding, where the electrons are picked up by another atom, in metallic bonding the electrons float about freely within the structure. The attraction between the negative electrons and the positive metal ions holds the metal together.

    A metal bond is the electrostatic attraction between delocalised electrons and positive metal ions.

    Bonding, metallic bonding example Sodium, StudySmarterFig. 4 - Metallic bonding in sodium. Each sodium atom loses an electron to form a positive ion. The electrons are delocalised and move about within the structure

    Intermolecular forces

    As you now know, substances made from two or more atoms joined together by chemical bonds are called molecules. For example, two hydrogen atoms and one oxygen atom bond to form a water molecule. We know that bonds are found within molecules. What forces are found between molecules?

    The answer is Intermolecular Forces, which can also be known as secondary bonds. There are three different types:

    • Van der Waals forces.
    • Permanent dipole-dipole forces.
    • Hydrogen bonding.

    Van der Waals forces

    Van der Waals forces are the weakest type of intermolecular force. They occur between all molecules. The random movement of electrons within a molecule causes a temporary dipole, which induces a dipole in a neighbouring molecule. The attraction between the two dipoles holds the molecules together.

    Permanent dipole-dipole forces

    In some molecules, the electrons are permanently distributed in an uneven manner. This means that one side of the molecule is constantly more negative than the other, and we call this a permanent dipole. Oppositely charged dipoles attract each other. The forces are known as permanent dipole-dipole forces and are stronger than van der Waals forces.

    Hydrogen bonding

    Some molecules containing hydrogen atoms experience an even stronger type of intermolecular force that we call hydrogen bonding. It occurs between molecules that have a hydrogen atom bonded to an oxygen, nitrogen or fluorine atom.

    The following diagram ranks the different types of primary and secondary bonds, also known respectively as intramolecular and intermolecular forces, according to their relative strength.

    Although hydrogen bonds are the strongest type of intermolecular force, they are still much weaker than intramolecular forces such as covalent, ionic and metallic bonds. For a more detailed look into different types of bonding and forces, check out Covalent Bond, Ionic Bonding, Metallic Bonding and Intermolecular Forces.

    Bonding, relative strength bonding intermolecular intramolecular forces, StudySmarterFig. 5 - A diagram showing the relative strengths of intermolecular and intramolecular forces

    Bonding and structure

    You can probably guess just by looking at everyday objects around you that different types of bonding produce very different types of structures. Take a diamond ring, for example. The metal that makes up the ring is easily melted or beaten into its circular torus shape, but the diamond embedded in the centre is extremely hard and strong. In fact, diamond doesn’t melt at all under normal atmospheric conditions. If you heat it to extremely high temperatures, it simply sublime, i.e., turns straight into a gas.

    This is because metals bond using metallic bonds whilst diamond uses covalent bonds. This gives the two substances very different structures and properties. However, oxygen is also a covalent molecule, but it behaves completely differently from a diamond! Look at their states of matter, for example. We just learnt that a diamond needs extreme temperatures before it sublimes, but oxygen, by contrast, is a gas at room temperature. We can therefore deduce that it isn’t just the type of bonding that affects a molecule’s properties, but also the structure and arrangement of atoms and the way the bonds hold the molecule together. The following table gives a summary of the different types of structures we find in chemistry.

    Bonding, structures comparison, StudySmarterFig. 6 - A table comparing different structures caused by bonding

    Bonding and shape

    We learnt above about how metals and ionic substances form lattices. Some covalent substances do too.

    A lattice is a regularly repeating arrangement of atoms or molecules.

    For example, the ionic lattice sodium chloride alternates positive sodium ions and negative chloride ions. However, a simple covalent molecule doesn’t have a lattice structure. Instead, it forms a molecule with a specific shape, depending on the number of electron pairs and covalent bonds it contains.

    Molecule shape is dictated by electron pairs. Imagine two magnets. If you hold the two south poles near each other, they will try to separate. This is because similar charges repel each other. Electron pairs are much the same. Put a group of electron pairs together in the shell of an atom and they’ll repel each other, trying to spread out as far apart as possible. If all the electron pairs are part of covalent bonds, the bonds will be equally spaced apart. But electron pairs that aren’t part of a bond, known as lone pairs, have a stronger repulsive force than bonded pairs. They repel other electron pairs more and squash the bonded pairs closer together.

    An example is methane, or \(CH_4\) . It has four electron pairs in its outer shell. They are all bonded pairs and repel each other equally. The angle between each of the bonded pairs is 109.5°. Water \(H_2O\) also has four electron pairs in its outer shell. However, two of the pairs aren’t bonded - they are lone electron pairs. This squashes the bond angle to just 104.5°.

    The following table summarises the shapes of different covalent molecules. There are also diagrams to help you consolidate your knowledge.

    bonding, table comparing different shapes of molecules, StudySmarterFig. 7 - A table comparing the different shapes of molecules

    Bonding - Key takeaways

      • Bonding is the interaction between different atoms to form molecules, compounds, and all other substances that make up the everyday world around us.
      • Atoms bond in order to achieve a more stable energy state. This usually happens by moving electrons about to achieve a full outer electron shell, like that of a noble gas.
      • Primary bonds are also known as intramolecular forces and occur within molecules. They are much stronger than secondary bonds, also known as intermolecular forces. Secondary bonds occur between molecules.
      • The three types of primary bonding are covalent, ionic, and metallic bonding.
      • The three types of secondary bonding are van der Waals forces, permanent dipole-dipole forces and hydrogen bonding.
      • Bonding influences a molecule or compound’s shape, structure and properties.
    Frequently Asked Questions about Bonding

    What is a chemical bond?

    A chemical bond is the interaction between different atoms to form a molecule or compound, due to lasting attraction between positive and negative charges.

    What is a covalent bond?

     A covalent bond is a shared pair of electrons.

    What is an ionic bond?

    An ionic bond is the electrostatic attraction between oppositely charged ions.

    What is a metallic bond?

    A metallic bond is the electrostatic attraction between positive metal ions and delocalised electrons.

    How are covalent bonds formed?

    Covalent bonds are formed when atoms share a pair of electrons. Each atom provides one electron from its outer shell, which join to form a shared pair.

    Test your knowledge with multiple choice flashcards

    Forces within molecules are known as:

    Forces between molecules are known as:

    What type(s) of atoms do covalent bonds involve?


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