When elements react, their atoms join with other atoms to form compounds. This involves giving, taking or sharing electrons to form ions or molecules. Compounds formed from metals and non-metals consist of ions (electrically charged particles) - hence called ionic compounds.
Metals lose electrons to form positive ions, whereas non-metals gain electrons to form negative ions - but only in terms of single electron transfers. E.g. metallic sodium forms a sodium ion by electron loss: Na ==> Na+ + e- , and non-metal chlorine atoms form a chloride ion by electron gain: Cl + e- ==> Cl-. Compounds formed from non-metals consist of molecules. In molecules the atoms are held together by covalent bonds, hence know as covalent compounds.
Chemical reactions can be represented by word equations or by symbol equations.
No atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants. This is known as the law of conservation of mass. In terms of masses involved of chemical reactions, you only need to appreciate law of conservation of mass.
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