COMPOUNDS AND FORMULA
A compound is a pure substance formed by chemically combining at least two different elements. Compounds are two or more different elements combined. Their atoms have been joined or bonded together.
Compounds can be represented by a FORMULA.
There must be at least two different types of atom (elements) in a compound. Compounds have a fixed composition and therefore a fixed ratio of atoms represented by a fixed formula, however the compound is made or formed.
In a compound, the elements are not easily separated by physical means, and quite often not easily by chemical means either.
A compound has properties quite different from the elements it is formed from. For example, soft silvery reactive sodium + reactive green gas chlorine colourless, not very reactive crystals of sodium chloride.
Chemical word equations
For any reaction, what you start with are called the reactants, and what you form are called the products. So any chemical equation shows in some way the overall chemical change of.
REACTANTS -> PRODUCTS
This can be written in words or symbols/formulae. The arrow means the direction of change from reactants =to=> products No symbols or numbers are used in word equations.
Always try to fit all the words neatly lined up from left to right, especially if it is a long word equation.
The word equation is presented to summarise the change of reactants to products.
Here are some word equations
Iron + sulphur -> iron sulphide
Sodium hydroxide + hydrochloric acid -> sodium chloride + water
Magnesium + hydrochloric acid -> magnesium chloride + hydrogen
Magnesium hydroxide + nitric acid -> magnesium nitrate + water