History of the Periodic Table Chapter 6

Dobereiner First person to create reasonably accurate measurements for atomic mass.

Newlands In 1864, Newlands proposed an organization scheme for the elements By arranging them in order of increasing atomic mass, he realized that their properties repeated every eighth element. He called this periodicity the Law of Octaves. Acceptance of his arrangement wasn’t immediate because it didn’t work universally in predicting chemical properties.

Meyer & Mendeleev In 1869, Lothar Meyer demonstrated a connection between atomic mass and elemental properties. In 1869, a Russian chemist named Dimitri Mendeleev also came up with a way of organizing the elements that were known at the time. Both chemists set the elements out in order of atomic mass Both then grouped them into rows and columns based on their chemical and physical properties. Mendeleev predicted the existence and properties of undiscovered elements, which is largely why his table got such wide acceptance.

Mendeleev’s Early Periodic Table, Published in 1872

Moseley Instead of ordering elements by total atomic mass, order by proton (atomic) number. This creates some minor shufflings in Mendeleev’s table and allows us to better predict unknown elements.

The Modern Periodic Table Chapter 6

Arrangement and Nomenclature Rows are called periods Columns are designated as groups Each column in the main table and each row at the bottom is also designated an individual family Groups 1A, 2A, and 3-8A are the main groups, or representative elements Groups 1B-8B are called the transition elements

The Periodic Table With Atomic Symbols, Atomic Numbers, and Partial Electron Configurations

Broad Periodic Table Classifications Representative Elements (main group): filling s and p orbitals (Na, Al, Ne, O) Transition Elements: filling d orbitals (Fe, Co, Ni) Lanthanide and Actinide Series (inner transition elements): filling 4f and 5f orbitals (Eu, Am, Es)

Information Contained in the Periodic Table Each group member has the same valence electron configuration (these electrons primarily determine an atom’s chemistry). The electron configuration of any representative element.

Information Contained in the Periodic Table Certain groups have special names (alkali metals, alkaline earth metals, chalcogens, halogens, etc). Metals and nonmetals are characterized by their chemical and physical properties.

Special Names for Groups in the Periodic Table

Metals Metals makeup more than 75% of the elements in the periodic table. Metals are characterized by the following physical properties: They have metallic shine or luster. They are usually solids at room temperature. They are malleable. Malleable means that metals can be hammered, pounded, or pressed into different shapes without breaking. They are ductile meaning that they can be drawn into thin sheets or wires without breaking. They are good conductors of heat and electricity.

Metals (cont) All B and most A elements are metals. The B  At stairstep designates the border between metals and non-metals 1A elements are alkali metals They are soft shiny metals that usually combine with group VIIA nonmetals in chemical compounds in a 1:1 ratio. 2A elements are the alkaline earth metals Both alkali and alkaline earth metals are chemically reactive, but 2A metals are less reactive than 1As. They combine with the group VIIA nonmetals in a 1:2 ratio.

Transition Metals & Metalloids The remaining 1-8B elements are all transition elements The transition elements also have valence electrons in two shells instead of one. Inner transition metals The lanthanide and actinide series comprise the inner transition metals

Metalloids Metalloids have characteristics of both metals and nonmetals and so can’t be classified as either, but something in between. They are good conductors of heat and electricity They are not good conductors or insulators. The six metalloids are B, Si, Ge, As, Sb, and Te.

Nonmetals There are 17 nonmetals in the periodic table, and they are characterized by four major physical properties. They rarely have metallic luster. They are usually gases at room temperature. Nonmetallic solids are neither malleable nor ductile. They are poor conductors of heat and electricity. The elements above the B  At stairstep are nonmetals

Nonmetals (cont) Group 6A contains the chalcogen elements Group 7A contains the highly reactive halogen elements They are fluorine, chlorine, bromine, and iodine. The halogens exist as diatomic molecules in nature. Group 8A comprises the completely non-reactive noble gases The noble gases are also called rare gas elements, and they all occur in nature as gases. The noble gases fulfill the octet rule by having a full outer level with 8 valence electrons. Therefore, they do not undergo chemical reactions because they do not accept any electrons.

Valence Electrons and the Periodic Table Valence Electrons and Group Atoms in the same group have the same chemical properties because they have the same number of valence electrons. Moreover, they have the same outermost orbital structure E.g. 1A elements all have s1 valence electrons E.g. 2A elements all have s2 valence electrons Valence Electrons and Period The primary quantum number (n) for an element’s valence electrons is the same its period. E.g. Lithium’s valence electron is n=2 and Li is found in the 2nd period

The Octet Rule Atoms tend to lose, gain, or share electrons until they are surrounded by 8 valence electrons