Atoms, Elements, Compounds and Mixtures

Atoms, Elements, Compounds and Mixtures

1. Chapter 1

   • Atoms, Elements and Compounds
     • an atom is the smallest part of an element that can exist
       • all substances are made of atoms
     • an element is a substance that only contains one sort of atom
       • there are about 100 different elements
       • elements are displayed on the periodic table
       • the atoms of each element are represented by a different chemical symbol
     • a compound contains atoms of two or more elements, which are chemically combined in fixed proportions
       • most substances are compounds
       • compounds are represented by a combination of numbers and chemical symbols called "chemical formulae"
       • compounds can only be separated into their component elements by chemical reactions or electrolysis
     • Scientists use chemical formulae to show
       • the different elements in a compound
       • how many atoms of each element one molecule of the compound contains
   • Equations
     • you can sum up what has happened during a chemical reaction by writing a word equation or balanced symbol equation
     • the reactants are on the left hand side of the equation
     • the products are on the right hand side of the equation
     • the total mass of the products in a chemical reaction is always equal to the amount of reactants
       • no atoms are lost or made
     • the products are made from exactly the same atoms as the reactants
   • Separating Mixtures
     • Mixtures consist of two or more elements or compounds which are not chemically combined
       • the components of a mixture retain their own properties
       • mixtures can be separated by physical processes- these processes do not involve chemical reactions, so no new substances are made
     • Filtration is used to separate soluble solids from insoluble solids
     • Crystallisation is used to obtain a soluble solid from a solution
       • 1. The mixture is gently warmed
         • 2. The water evaporates leaving crystals of pure salt
     • Simple Distillation is used to obtain a solvent from a solution
     • Fractional Distillation is used to separate mixtures in which the components have different boiling points
     • Chromatography is used to separate the different soluble coloured components of a mixture

2. Chapter 2

3. Chapter 3