Unit 7: Naming and Formula Writing Objectives 1 and 2 Activity a

Vaughan Merrick

Atoms- The smallest particle of an element that retains the properties of that element. The chemist John Dalton described the atom using a copper penny. If you were to grind the penny into dust, the little specks of dust would still retain the properties of copper. If you continued to split the specks of dust and found a particle that if split, it would no longer have the properties of copper, then you have found one single atom of copper.

Molecules- The smallest electrically neutral unit of a substance that still has the properties of the substance. Molecules are made up of two or more atoms that act as one unit.

Formula units- This represents an ionic compound and it is the lowest whole-number ratio of ions in the compound. For example, in sodium-chloride, the lowest whole-number ratio of ions is 1:1, so the formula unit is NaCl.

Ionic compounds-These are compounds composed of cations and anions. They are usually composed of a nonmetal and metal anions. These compounds have high melting points usually above 300°C. At room temperature, these compounds exist in the solid state. In addition, its representative unit is the formula unit.

Molecular compounds-These are simply compounds composed of molecules. They must be electrically neutral and be combinations of molecules. These compounds have low melting and boiling points and at room temperature, can exist as liquids, gases or solids. Most of the molecules in molecular compounds are composed of the atoms of two or more nonmetals. This compounds representative unit is the molecule.