Identify the following as elements or compounds: \(\mathrm{NH}_{3}, \mathrm{~N}_{2}, \mathrm{~S}_{8}, \mathrm{NO}, \mathrm{CO}, \mathrm{CO}_{2}, \mathrm{H}_{2}, \mathrm{SO}_{2}\)

A chemical formula represents the composition of a molecule using the symbols of the elements and numerical subscripts to indicate the number of atoms of each element present in the molecule. Consider water (H_2O), which consists of two hydrogen atoms and one oxygen atom. This formula is not only a simple inventory of the elements, but also a blueprint that explains the molecule's structure. It implies that a water molecule is made by combining two hydrogen atoms with one oxygen atom.

In the provided exercise, NH_3 has a chemical formula showing one nitrogen atom combined with three hydrogen atoms, indicating a compound known as ammonia. Similarly, the CO_2 chemical formula signifies one carbon atom double-bonded to two oxygen atoms, which is recognized as carbon dioxide. By understanding chemical formulas, we can quickly identify the substances as either elements or compounds, and predict their physical and chemical properties.

The ability to identify atoms within a chemical formula is fundamental in chemistry. Atoms are the basic units of matter, and each atom corresponds to a specific element. In chemical formulas, the atomic symbol (such as 'C' for carbon, 'H' for hydrogen, or 'O' for oxygen) is used to indicate the type of atoms present in the molecule. Once identified, we can determine whether a substance is a pure element or a compound.

For example, the presence of only 'H' symbols makes H_2 an element—hydrogen. Conversely, the sample NH_3 combines atoms 'N' and 'H', making it easy to spot that it's a compound composed of nitrogen and hydrogen. Accurately identifying atoms within a formula is a skill that informs not only the classification of substances but also facilitates understanding of their chemical behavior and reactions.

Molecular composition refers to the specific arrangement and number of atoms that make up a molecule. Knowing the number and type of atoms, as we do from identifying the atoms in chemical formulas, allows us to describe the molecular composition. Compounds, such as SO_2, are made by bonding atoms of different elements in definite proportions. Here, sulfur and oxygen combine to form sulfur dioxide, a compound with a particular molecular composition.

In contrast, elements like S_8 display a molecular form consisting of a single type of atom; sulfur in this case. The subscript '8' indicates eight sulfur atoms are connected, probably in a ring structure, a common form for elemental sulfur. Understanding molecular composition is crucial in predicting how molecules will interact, their physical characteristics, and the roles they play in various chemical processes.