Chapter 1 – Quantitative Chemistry
SOME FUNDAMENTAL CONCEPTS
Matter can be divided into mixtures and pure substances. Mixtures consist of a number of different substances, not chemically combined together. The different components of a mixture often have different physical properties (Such as melting point and density) and chemical properties (such as flammability and acidity). All samples of a pure substance have identical chemical properties, for example pure water from any source freezes at exactly 0’ C.
Pure substances may be further divided into elements and compounds. The difference between these is that an element cannot be split up into any simpler substances by chemical means, whilst a compound can be changed into more basic components.
All substances are made up of very tiny particles called atoms. Atoms are the smallest particles in an element, as they cannot be split by chemical means.
An element is a substance that contains only one type of atom, so it cannot be converted into more chemical means. Some elements are composed of a mixture of closely related atoms called isotopes. All elements have distinct names and symbols. Atoms can join together by chemical bonds to form compounds. In a compound, the constituent elements will be present in fixed proportions as H2O (water), H2SO4 (Sulfuric Acid), CO2 (Carbon dioxide) and NH3 (ammonia). The only way to separate a compound into it’s component elements is by a chemical change that breaks some bonds and forms new ones, resulting in new substances.
If a substance contains different types of particles, then it is a mixture.
Element | Compound | Mixture |
-0-0-0-00-0-0-0-0 | -0-0-0-0-0-0-0-0-0 | -0-0-0-0-0-0-0-0 |
Molecule refers to a small group of atoms joined together by covalent bonds. If the atoms are of the same kind, then it is a molecule of an element, if different it is a molecule of a compound. Most elements that are gases are diatomic (composed of molecules...