Element and compounds By the end of this session you should be able to.... 1) Explain what element symbols, chemical formulae and equations tell us 2) Describe the structure of an atom, and calculate the number of protons, electrons and neutrons in an element. 3) Understand the basis of chemical equations and how to balance them Element symbols Chemical formulae Elements are combined to make compounds with specific combinations Sodium Chloride Calcium carbonate NaCl CaCO3 Oxygen O2 Copper sulphate CuSO4.5H2O Are these atoms, molecules, elements or compounds? Term Definition Example Atom The smallest part of a substance that cannot be broken down by chemical means Sodium, Na Molecule Two or more atoms joined together A substance that cannot be broken down Oxygen O2 Element Compound Oxygen O2 Sodium, Na A substance made up of two Glucose C6H12O6 or more elements Table salt – Sodium chemically joined together chloride (NaCl) Which is the odd one out and why? Calcium Chlorine Carbon dioxide Atomic Structure 500 BC 1800 1900 2000 Relative size and charge of sub atomic particles Particle Size Charge Proton 1 +1 Neutron 1 0 Electron 1/1840 -1 In any atom, the number of protons and electrons is equal so that the atom has a neutral electrical charge overall. Every element has a distinct number of protons, electrons and neutrons. Atomic mass = protons + neutrons Atomic (proton) number = protons = electrons 7 Li 3 Task: Calculate the number of protons, electrons and neutrons in the following elements: Element Atomic number Atomic mass Lithium 3 7 Nitrogen 7 14 Chlorine 35 17 35 Chlorine 36 17 36 Lead 82 207 Protons Electrons Neutrons Chemical equations Chemical equations show us what happens when different substances react together. Reactants → Products What ever atoms are on the left must be present on the right, just in a different combination. For example, Carbon + oxygen → carbon dioxide C (s) + O2 (g) → CO2 (g) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g) Sodium + water → sodium hydroxide + hydrogen 2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g) Na H O Can you..... 1) State the combination of elements in iron hydroxide – Fe(OH)3? 2) Explain the difference between an atom and molecule? 3) Explain the key steps to balancing an equation?