Select the elementary substance.
silicon dioxide (SiO2) tin (Sn) phosphine (PH3)
Every substance around you is made of one or more chemical elements, or types of atoms. Substances that are made of only one chemical element are elementary substances. Substances that are made of two or more chemical elements bonded together are compounds.
Every chemical element is represented by its own symbol. For some elements, the symbol is one capital letter. For other elements, the symbol is one capital letter and one lowercase letter. For example, the symbol for the element fluorine is F, and the symbol for the element beryllium is Be.
The symbol for each element in a substance is shown in the substance's chemical formula.
An elementary substance is represented by a chemical formula that contains only one symbol.
The symbol may be followed by a subscript. A subscript is text that is smaller and placed lower than the normal line of text. A subscript is included when the atoms in the elementary substance are bonded to form molecules. The subscript tells you the number of atoms in each molecule.
For example, the chemical formula for the elementary substance oxygen is O2. The formula has a subscript of 2. This subscript tells you that there are two atoms in the molecule represented by this chemical formula.
The chemical element represented by the symbol O is also called oxygen. So, the formula O2 tells you that each molecule of O2 contains two oxygen atoms.
A compound is represented by a chemical formula that contains multiple symbols.
For example, in the compound beryllium fluoride, there is one beryllium atom for every two fluorine atoms. This combination is shown in the compound's chemical formula, BeF2. In the formula, the symbol Be represents one beryllium atom. The symbol F followed by the subscript 2 represents two fluorine atoms.
Look at the chemical formula for each substance, and count the number of symbols in the formula. Then, decide if the substance is an elementary substance. The chemical formula for tin contains one symbol: Sn. So, tin is made of one chemical element. Substances that are made of one chemical element are elementary substances. So, tin is an elementary substance. The chemical formula for phosphine contains two symbols: P for phosphorus and H for hydrogen. So, phosphine is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, phosphine is a compound, not an elementary substance. The chemical formula for silicon dioxide contains two symbols: Si for silicon and O for oxygen. So, silicon dioxide is made of two chemical elements bonded together. Substances that are made of two or more chemical elements bonded together are compounds. So, silicon dioxide is a compound, not an elementary substance.