Periodic Table Section 18.3

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

Mendeleev

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

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

Energy levels of electrons Sublevel# e in sublevelShape s2sphere p6 dumbbell d10 double dumbbell f14 complex es/shapes.html

Energy levels of electrons Level 1 s 2 electrons Level 2 s & p = 8 electrons Level 3 s, p, d = 18 e - Level 4 s,p,d,f = 32 e - Valence Electrons Group 1A – 8A have 1-8 valence electrons

Periodic Table, Valence electrons, and Diatomics

Dot Diagrams Electron dot diagram (or Lewis dot diagram) - A symbol of an element surrounded by dots to represent electrons in the outer energy level First 2 electrons go together Next electrons go one on each side, then start to double up

Valence electrons Properties of elements in the same group- similar due to same # of valence electrons Alkali metals- group 1A- very reactive metals Alkaline metals- group 2 A- less reactive than alkali Halogens- group 7A Likely to react with Alkali metals- group 1A

Arrangement of Periodic Table Noble Gases- group 8A- not reactive- don’t form compounds