Periodic Table Section 18 3 Periodic Table l

Periodic Table Section 18. 3

Periodic Table l Periodic- Repeated in a pattern l Elements are ordered by: increasing atomic number l changes in physical & chemical properties l l Mendeleev- mass Ordered elements by atomic Left blank places in his table to line up elements according to their properties l Elements were later discovered and fit into the places he left blank l

Periodic Table l Moseley- organized elements by atomic number rather than atomic mass l Same arrangement as today l Groups/Families- periodic table l Electrons vertical columns of the Around the nucleus in an electron cloud l Energy levels dictate location of electrons l Closer to nucleus = less energy l Fill energy levels from inner to outer levels l

Electrons l Electrons in outer shell – determine chemical properties of elements l Complete outer shell- needs 8 electrons to be stable l Energy levels and # of electrons in each: Level 1 l Level 2 l Level 3 l Level 4 l Holds 2 Holds 8 Holds 18 Holds 32

Valence Electrons l Group 1 A – 8 A have 1 -8 valence electrons- See periodic table for details l Electron dot diagrams- A symbol of an element surrounded by dots to represent electrons in the outer energy level l Properties of elements in the same group - similar due to same # of valence electrons

Arrangement of Periodic Table l Halogens- group 7 A l Likely to react with Alkali metals- group 1 A Rows of Periodic Table- periods l Properties of metals- lustrous, conductive for heat and electricity, malleable, ductile (located in middle and left of periodic table) l Properties of nonmetals- brittle, often gases, don’t conduct l Properties of metalloids- have properties of both metals and nonmetals l

Building Blocks of Universe l Hydrogen l and Helium Combine to form elements with larger atomic numbers – can only occur through nuclear reactions