<Tr> <Td> Periodic table history (show) <Ul> <Li> Dmitri Mendeleev <Ul> <Li> predictions </Li> </Ul> </Li> </Ul> <Ul> <Li> Discovery of elements </Li> </Ul> <Ul> <Li> Naming & etymology </Li> </Ul> <Ul> <Li> <Ul> <Li> for places </Li> <Li> for scientists </Li> <Li> controversies </Li> </Ul> </Li> </Ul> <Ul> <Li> (in East Asia) </Li> </Ul> <Ul> <Li> Systematic element names </Li> </Ul> </Td> </Tr> <Ul> <Li> Dmitri Mendeleev <Ul> <Li> predictions </Li> </Ul> </Li> </Ul> <Li> Dmitri Mendeleev <Ul> <Li> predictions </Li> </Ul> </Li> <Ul> <Li> predictions </Li> </Ul>

How many energy levels are on the current periodic table