Looking at the atomic and molecular level when chemical and physical changes occur can give us insight into the differences between the two. Covalent bonds are bonds where electrons are shared between atoms. Chemical changes occur when covalent bonds are broken and new covalent bonds are formed. During physical changes, covalent bonds are not broken and formed. Please give an example of both.
Chemical changes destroy existing covalent bonds and form new ones, changing the chemical composition of matter, and an example of this is burning a piece of wood. This destroys existing bonds, and the resulting ash will have a chemical composition different from that of the original wood. During a physical change, chemical composition is not altered and no bonds are destroyed or created. For example, once chopped, a piece of wood will retain its chemical composition.
Covalent bonds, also known as molecular bonds, exist when pairs of electrons (known as shared pairs or bonding pairs) are shared between atoms, creating a stable equilibrium of attraction and repulsion.
One of the main differences between chemical and physical changes is how they impact covalent bonds. During a chemical change, existing covalent bonds are broken and new covalent bonds are formed. This type of change alters the chemical composition of the substance and cannot be easily reversed.
Contrariwise, covalent bonds are neither formed nor broken during a physical change. Physical changes can result in a difference in appearance, size, or shape, but they do not alter the chemical composition of matter. The matter retains its original composition after a physical change. Physical changes neither create nor destroy substances, while chemical changes destroy existing matter and create new matter.
An example of a chemical change is burning wood. As wood burns, the original covalent bonds are destroyed. The burned wood becomes ash and now has new covalent bonds and a new chemical composition. If we were to take a piece of wood and cut it, rather than burn it, this would demonstrate a physical change. The appearance of the chopped wood would differ from the appearance of the wood prior to cutting; however, there would be no change in the chemical composition of the wood.
Another example of a chemical change is burning paper. The existing covalent bonds will be destroyed as the paper burns, and new bonds will be formed. The resulting ash will differ in chemical composition from the original paper. If the paper were torn or shredded instead of burned, this would be a physical change. The appearance of the paper would be altered, but the paper would retain its chemical composition. Burning the paper destroys its existing covalent bonds and forms new ones as the paper is transformed to ash. Tearing or shredding the paper has no impact on its chemical composition. No bonds are destroyed or formed during a physical change.
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