2. Definition of a chemical compound A compound is a substance formed when two or more chemical elements are chemically bonded together. Two types of chemical bonds common in compounds are covalent bonds and ionic bonds. The elements in any compound are always present in fixed ratios. Example 1: Pure water is a compound made from two elements - hydrogen and oxygen. The ratio of hydrogen to oxygen in water is always 2:1. Each molecule of water contains two hydrogen atoms bonded to a single oxygen atom. Example 2: Pure table salt is a compound made from two elements - sodium and chlorine. The ratio of sodium ions to chloride ions in sodium chloride is always 1:1. Example 3: Pure methane is a compound made from two elements - carbon and hydrogen. The ration of hydrogen to carbon in methane is always 4:1. Compounds can be decomposed chemically into their constituent elements. Source: chemicool.com

3. Physical and chemical properties of bases Property Acid Base Taste sour (vinegar) Bitter (Baking soda) Smell Frequently burns nose usually no smell Texture sticky slippery Reactivity frequently reacts with metal react with many oils and fats It's frequently possible to tell acids and bases apart from one another by some of their easily observed chemical and physical properties. A table of these properties is shown here:

4. Formula and names of bases Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. Fe3C is the chemical formula for steel.

5. More properties of bases In chemistry, a base is a substance that, in aqueous solution, is slippery to the touch, tastes bitter, changes the colour of indicators (e.g., turns red litmus paper blue), reacts with acids to form salts, and promotes certain chemical reactions (base catalysis). Examples of bases are the hydroxides of the alkali and alkaline earth metals (NaOH, Ca(OH)2, etc). Such substances produce hydroxide ions (OH-) in aqueous solutions, and are thus classified as Arrhenius bases Source: wikipedia.org