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Chemical reactions reactants + products A chemical reaction is a change that takes place when one or more substances (called reactants) form one or more new substances (called products). Bonding and electrons • When elements react, their atoms join with other atoms to form molecules and/or compounds. This is Bonding. • Bonding involves giving, taking or sharing electrons to form ions or molecules Metals bonding with Non-metals • Compounds formed from metals and non metals consist of ions. • Metals lose electrons to form positive ions. • Non metals gain electrons to form negative ions Word and symbol equations + Word equation: carbon + oxygen carbon dioxide Symbol equation: C(s) + O2(g) CO2(g) • 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 products equals the mass of the reactants HT candidates should be able to balance symbol equations A symbol equation must be balanced to give the correct ratio of reactants and products. Limestone = calcium carbonate • Limestone is mainly composed of the compound calcium carbonate (CaCO3) • Limestone is quarried (dug up) and can be used as a building material Heating calcium carbonate • Calcium carbonate can be decomposed by heating (thermal decomposition) to make calcium oxide and carbon dioxide • The carbonates of magnesium, copper, zinc, calcium and sodium decompose on heating in a similar way Limestone cycle Summary of limestone chemistry Limestone and its products can be involved in various useful chemical reactions: thermal decomposition of limestone calcium carbonate calcium oxide carbon dioxide + production of calcium hydroxide + calcium oxide water calcium hydroxide using limewater to test for carbon dioxide. calcium hydroxide (aq) + carbon dioxide calcium carbonate + water Making building materials Limestone + Cement Cement + + Clay Cement Sand Mortar Sand and aggregates Concrete Limestone is heated with clay to make cement. Cement is mixed with sand to make mortar and with sand and aggregates to make concrete Carbonates and acid Carbonates react with acids to produce carbon dioxide. Limestone is damaged by acid rain Pros and cons of quarrying