Chemical bonding is the process of two or more atoms coming together to form a molecule.
Chemical bonding occurs when two or more atoms come together to form a molecule. It is a general principle of science that all systems will try to reach their lowest energy level, and chemical bonding will only occur when a molecule can be formed with less energy than its uncombined atoms. The three main types of bonding are ionic, covalent, and metallic. They all involve electrons moving between atoms in various ways. Another much weaker type is the hydrogen bond.
atomic structure
Ions are atoms with negative or positive electrical charges.
Atoms consist of a nucleus containing positively charged protons, which is surrounded by an equal number of negatively charged electrons. Normally, therefore, they are electrically neutral. However, an atom can lose or gain one or more electrons, giving it a positive or negative charge. When someone has an electrical charge, it is called an ion.
It is the electrons that are involved in the chemical bond. These particles are organized in layers that can be considered to exist at increasing distances from the nucleus. In general, the further away the shells are from the nucleus, the more energy they have. There is a limit to the number of electrons that can occupy a shell. For example, the first innermost shell has a limit of two and the next shell has a limit of eight.
In most cases, it is only the outermost shell electrons that participate in the bond. These are often called valence electrons. As a general rule, atoms tend to combine with each other so that they all reach full outer shells, since these configurations generally have lower energy. A group of elements known as the noble gases – helium, neon, argon, krypton, xenon and radon – already have complete outer shells and therefore do not normally form chemical bonds. Other elements will generally try to achieve a noble gas structure by giving, accepting, or sharing electrons with other atoms.
Chemical bonds are sometimes represented by something called a Lewis structure, named for the American chemist Gilbert N. Lewis. In a Lewis structure, valence electrons are represented by dots outside the chemical symbols for elements in a molecule. They clearly show where electrons have moved from one atom to another and where they are shared between atoms.
ionic bond
This type of chemical bond occurs between metals, which easily give up electrons, and non-metals, which want to accept them. The metal supplies the electrons in its incomplete outermost shell to the nonmetal, leaving that shell empty so that the entire shell below becomes its new outermost shell. The nonmetal accepts electrons to fill its incomplete outermost shell. In this way, both atoms achieved full outer shells. This leaves the metal positively charged and the nonmetal negatively charged, so they are positive and negative ions that attract each other.
A simple example is sodium fluoride. Sodium has three shells, with a valence electron in the outermost part. Fluorine has two shells, with seven electrons in the outer shells. Sodium gives up its single valence electron to the fluorine atom, so sodium now has two full shells and a positive charge, while fluorine has two full shells and a negative charge. The resulting molecule, sodium fluoride, features two atoms with complete outer shells held together by electrical attraction.
Covalent bond
Non-metal atoms combine with each other by sharing electrons in such a way as to lower their overall energy level. This generally means that when combined they all have full outer layers. To take a simple example, hydrogen has only one electron, in its first and only shell, leaving it with less than a full shell. Two hydrogen atoms can share their electrons to form a molecule in which they both have a complete outer shell.
How atoms will combine with each other can often be predicted from the number of electrons they have. For example, carbon has six, meaning it has a full first shell of two and an outer shell of four, leaving it four short of a full outer shell. Oxygen has eight and thus six in its outer shell, two short of a full shell. One carbon atom can combine with two oxygen atoms to form carbon dioxide, in which carbon shares its four electrons, two with each oxygen atom, and the oxygen atoms share two of their electrons with each other. electrons with the carbon atom. Thus, all three atoms have complete outer shells containing eight electrons.
metallic union
In a piece of metal, the valence electrons are more or less free to move, rather than belonging to individual atoms. Therefore, the metal consists of positively charged ions surrounded by negatively charged mobile electrons. Ions can be moved about relatively easily, but are difficult to separate due to their attraction to electrons. This explains why metals are generally easy to bend but difficult to break. The mobility of electrons also explains why metals are good conductors of electricity.
hydrogen bonds
Unlike the examples above, hydrogen bonds involve bonds between molecules, rather than within them. When hydrogen combines with an element that strongly attracts electrons, such as fluorine or oxygen, the electrons are separated from the hydrogen. This results in a molecule with an overall positive charge on one side and a negative charge on the other. In a liquid, the positive and negative sides attract each other, forming bonds between the molecules.
Although these bonds are much weaker than ionic, covalent, or metallic bonds, they are very important. Hydrogen bonds take place in water, a compound that contains two hydrogen atoms and one oxygen. This means that more energy is required to convert liquid water to gas than would otherwise be the case. Without hydrogen bonding, water would have a much lower boiling point and would not be able to exist as a liquid on Earth.