What products are obtained in the electrolysis of a molten mixture of KI and KBr?
Chapter 7: Periodic Properties of the Elements Monday, October 17, 2016 2:56 PM 7.1 Development of the Periodic Table Mendeleev and Meyer in 1869 group the elements by properties Groups 1A through 7A are representing s and p subshells Elements are grouped by metals, nonmetals and metalloids Groups are arranged by valence electrons (electrons that are involved in chemical reactions) Topics covered: • Effective nuclear charge (eff effect of protons on electrons • Atomic sizes Effective nuclear charge Chemical properties are determined by • Number of valence electrons • How strongly these electrons are attracted to the nucleus Core electrons are all electrons but valence electrons The effects of increasing nuclear charge can be illustrated by looking at core electrons. Electrons are attracted to the nucleus, but they also repel one another. Valence electrons are repelled by the inner core electrons, shielding effect. The effective nuclear charge is the charge felt by the outermostvalence elctrons. ZeffZ - S Z= atomic number (protons) S= Core electrons The effective nuclear charge is smaller than the charge of the nucleus because of shielding. Across a period: S remains constant while Z increases, thereforeff increases. Li Be B C N O F Z 3 4 5 6 7 8 9 Core 2 2 2 2 2 2 2 Zeff 1 2 3 4 5 6 7 Across a group: Zeffmain