Learn about the different electron shells of atoms as well as the octet rule for valence electrons and how that applies to covalent bonding. Discover the definition of covalent bonding and the relationships between atoms.
The octet rule states that atoms strive to have eight electrons in their outer shells
Before we start this lesson, let's refresh your memory a bit with things you may know or things you may remember hearing about. Atoms are composed of protons and neutrons that live in the nucleus and electrons that orbit the nucleus in energy levels. Most atoms are combined into molecules. A molecule is a neutrally charged group of atoms that is held together by bonds.
Electrons orbit the nucleus of an atom in energy levels or shells. In all but the smallest atoms, the outer energy shell likes to have eight electrons in it. Atoms love to have their outer shells filled with eight electrons. This is called the octet rule. If an atom doesn't have its outer shell full of eight electrons naturally, it will try to fill it by bonding with other atoms. Sometimes an atom will lose an electron or two or three in order to have its outer shell full. Sometimes it gains electrons. It all depends on what's easier. If there are only two electrons in the outer shell, it is easier to lose two than to gain six. If it loses two electrons, the lower shell, which is now the outer shell, will still be full, so it is still happy.
Atoms like to be stable. They go to great lengths to be stable and happy. Stability to an atom is a complete outer energy level. The outer energy level is full of the valence electrons. Valence electrons are the electrons in the highest occupied energy level of an atom. The number of valence electrons mostly determines the properties of an element.
An octet is a set of eight: think octopus (an animal with eight legs) or octagon (a figure with eight sides). In chemistry, the octet rule says that atoms like to have full outer shells of only eight electrons. Atoms will lose or gain valence electrons to make their outer shells full with eight electrons, and they do this by bonding with other atoms. Those atoms can be the same element, as when oxygen bonds with itself to form O2, or with different elements, such as water, H2O. The exceptions to the octet rule are hydrogen and helium, which are both happy with two electrons in their outer shells.
Valence electrons are the electrons that form chemical bonds
As in most things in this world, atoms, electrons, molecules, etc., like to be in a state where they exert the least amount of energy, just like you at the end of a long day. Lying on the couch and expending little energy seems like the best thing in the world. Atoms bond together because in doing so they enter a lower energy state. Compounds form when the outer shell electrons are lost or gained. The electrons that participate in chemical bonding are called the valence electrons.
When two atoms share electrons to fill their outer shells, it is called a covalent bond. A covalent bond is when atoms share one or more electrons. Covalent bonds form because the energy exerted to stay together is much less than the energy needed to break them apart and form isolated atoms. This is because the chemical reaction releases energy and each atom moves to a lower energy state when they enter the bond.
Properties of Covalent Bonds
Covalent compounds are formed when a compound is held together by bonds and the atoms share valence electrons. These elements are sharing their electrons because neither one of them has the strength to take the electrons from the other. Because they are sharing them rather than transferring them as they do in ionic bonds, the bond isn't as strong as other types.
Atoms are composed of protons and neutrons that live in the nucleus. Electrons orbit the nucleus of an atom in energy levels or shells. In all but the smallest atoms, the outermost energy shell likes to have eight electrons in it. This is called the octet rule. Atoms like to combine into molecules and compounds because they are at a lower energy state when they do so. When two atoms share their electrons to form a compound it is called a covalent bond, and the compound is called a covalent compound.
After working this lesson, you should be ready to:
- Define atoms
- Recognize electrons creating energy shells
- Recall the octet rule
- Explain atoms into molecules and compounds
- Locate what a covalent bond and compound is