Unit 3 Part 2 Chapter 5 Explain the trends of the periodic table based on the elements’ valence electrons and atomic numbers. (PS-2.3)

History of the Periodic Table First list of known elements compiled by Antoine Lavoisier in late 1790s Contained 23 elements ~70 known elements by 1870 1860s – search for relationships between atomic mass and elemental properties began

John Newlands (1837 – 1898) English chemist Elements arranged by increasing atomic mass, properties repeat every 8th element Pattern is called periodic b/c it repeats in specific manner Law of octaves Did not work for all known elements

Lothar Meyer (1830 – 1895) German chemist 1869 - Demonstrated connection between atomic mass and elemental properties

Lewis Reeve Gibbes (1810 – 1894) American chemist Professor of Chemistry at the College of Charleston 1839 – 1892 1870 – 1874 generated “Synoptical Table of the Chemical Elements” Not published until 1886

Dmitri Mendeleev (1834 – 1907) Russian chemist 1869 – published periodic table based on relationship between atomic mass and elemental properties Used table to predict existence and properties of undiscovered elements Left blank spaces in table Predicted existence of Scandium, gallium and germanium

Henry Moseley Errors in periodic table developed by Mendeleev (some elements in wrong groups) 1913 – Moseley regrouped elements by increasing atomic number Problems with order of elements solved

Periodic Law Periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number

Modern Periodic Table Periods Horizontal Rows Numbered 1 – 7 Groups Vertical Columns Numbered 1 – 18 Each member of the same group has the same number of valence electrons and similar properties Chemical properties are not the same because elements have different numbers of non-valence electrons Periods Horizontal Rows Numbered 1 – 7 Represents which energy level that the valence electrons can be found

Modern Periodic Table Representative Elements Transition Elements Groups 1A – 8A Possess wide range of chemical and physical properties Transition Elements Groups 1B – 8B

Metals Located left of the staircase Luster Malleable & ductile Good conductors High density React with acids

Metals Alkali Metals Alkaline Earth Metals Transition Metals Group 1A elements Most reactive metals Alkaline Earth Metals Group 2A elements Chemically reactive Transition Metals Inner Transition Metals Lanthanide Series Used as phosphors, emit light when struck by electrons Actinide Series

Alkali Metals Alkaline Earth Metals Transition Metals Lanthanide Series Actinide Series

Nonmetals Right of Staircase Dull Nonmalleable, non-ductile Poor conductors Low density Do not react with acids

Nonmetals Halogens Noble Gases Group 7A Highly reactive Group 8A Extremely unreactive

Noble Gases Halogens

Metalloids Along staircase May have characteristics of metals and/or nonmetals

Organizing Elements by Electron Configuration Valence Electrons Atoms in the same group have similar chemical properties because they have the same # of valence electrons Valence Electrons & Period Energy level of valence e- indicates the period on the periodic table Valence Electrons & Group Number Representative element’s group number is the same as its number of valence electrons

HW Question An unknown element has chemical behavior similar to that of silicon (Si) and lead (Pb). The unknown element has a mass greater than that of sulfur (S), but less than that of cadmium (Cd). Use the periodic table to determine the identity of the unknown element.

Periodic Table Trends Energy Levels Left to right across a period (Pds. 1 – 3) Energy level of valence electrons stays the same For example, all elements in Period 3 have valence electrons located in the 3rd energy level. Top to bottom down a group (Representative Elements) Energy level of valence electrons increases by one For example, Li has 1 valence electron in energy level 2 and Rb has 1 valence electron in energy level 5

Periodic Table Trends Valence electrons Left to right across a period (Pds. 1 – 3) Representative elements: # of valence electrons increases by 1 For example, Mg has 2 valence electrons in the 3rd energy level and P has 5 valence electrons in the 3rd energy level. Top to bottom down a group (Representative Elements) Elements in a group have an EQUAL number of valence electrons

Compare… Compare the number and location of the valence electrons in the following sets of elements: Ca & P Li & Cs Br & F Al & Kr Be & N