Who was Dimitri Mendeleev ? What are groups and periods? Bell Ringer Who was Dimitri Mendeleev ? What are groups and periods?

The Periodic Law Chapter 5

Search for order 1750 only 17 elements known 1789 Antoine Lavoisier grouped known elements (4 groups) Metals Non-metals Gases Earths Next 80 yrs. scientists looked for better way to classify known elements

History of the Periodic Table Dmitri Mendeleev (Father of the Periodic Table) Russian Chemist Used data from scientist before him to create the first periodic table. (1869) Mendeleev noticed that when elements were arranged in order of increasing atomic mass, certain similarities in their chemical properties appeared at regular intervals (such repeating pattern is referred to as periodic)

Mendeleev’s Periodic Table Contradiction: Mendeleev placed Iodine (atomic mass 127) after tellurium (atomic mass 128) Elements were placed in a group of elements with which they share similar properties. Mendeleev’s procedure left several empty spaces in his periodic table. In 1871, he predicted the existence and properties of the elements that would fill three of the spaces. By 1886, all three elements were discovered (Scandium,Gallium,& Germanium)

Mendeleev’s Periodic Table The success of Mendeleev’s predictions persuaded most chemist to accept his periodic table and earned him credit as the discoverer of the periodic law. Two Questions remained 1) why could most elements be arranged in order of increasing atomic mass but a few could not? 2)what was the reason for periodicity?

Mosely and the Periodic Law In 1911, the English scientist Henry Mosely (working with Rutherford) examined the spectra of 38 different metals. When analyzing his data, Mosely discovered a previously unrecognized pattern. The elements in the P.T fit better when they are arranged in increasing order to nuclear charge (# of protons in the nucleus). Mosely’s work led to both the definition of atomic number and the recognition that atomic number is the basis for the organization of the periodic table.

Periodic Law Mendeleev’s principle of chemical periodicity is correctly stated in what is known as the periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers.

The Modern Periodic Table Mendeleev P.T (50 elements) Discovery of new elements or synthesized in labs They can be placed in a group of elements wit similar properties. The periodic table is an arrangement of the elements in order of their atomic numbers so that elements with similar properties fall in the same column or group.

Modern Periodic Table Columns Rows -vertical (up & down) -called groups or families -#ed 1-18 or 1A through 8A -elements in same family have similar properties horizontal (left – right) -called a period -properties change greatly across period -first element in period is very active metal -last element in most periods is noble gas -7 periods (number them on your periodic table)

Metals Most solids (Hg is liquid) Luster – shiny. Ductile – drawn into thin wires. Malleable – hammered into sheets. Conductors of heat and electricity.

Non-Metals Properties are generally opposite of metals Poor conductors of heat and electricity Low boiling points Many are gases at room temperature Solid, non-metals are brittle (break easily) Chemical properties vary

Metalloids stair-step pattern Have properties similar to metals and non-metals Ability to conduct heat and electricity varies with temp Better than non-metals but not metals