7. The periodic table

Available for over a year

In this episode, Dr Sunayana Bhargava and Tulela Pea look at how the periodic table developed to the modern one we use today. Suitable for: AQA, Edexcel, OCR. For more information on the periodic table, check out the BBC Bitesize website: https://www.bbc.co.uk/bitesize/guides/zwt2k2p/revision/1 Key learning objectives discussed in this episode include: - Before the discovery of protons, neutrons and electrons, scientists attempted to classify the elements by arranging them in order of their atomic weights. - The early periodic tables were incomplete and some elements were placed in inappropriate groups. Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights. - Elements with properties predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct. The elements in the modern periodic table are arranged in order of atomic (proton) number and so that elements with similar properties are in columns, known as groups. - Elements in the same group in the periodic table have the same number of electrons in their outer shell (outer electrons) and this gives them similar chemical properties.