CHAPTER 5: THE PERIODIC LAW CHEMISTRY 1-2 ENRICHED MR. CHUMBLEY SECTION 1: HISTORY OF THE PERIODIC TABLE P. 125 - 129 DEVELOPING THE PERIODIC TABLE
By the mid 1800’s, over 60 elements has been discovered and identified
Chemists at this time, primarily examined the properties of known elements and compounds containing known elements
In September of 1860, the First International Congress of Chemists was assembled in Karlruhe, Germany to establish standards for determining atomic mass
Italian chemist Stanislao Cannizzaro presented a method to accurately measure relative masses of atoms
This method led to standard values for atomic mass MENDELEEV’S PERIODIC TABLE
Russian Chemist Dmitri Mendeleev wanted to organize the known elements by their properties
Mendeleev noticed that when elements were organized by atomic mass, certain properties appeared at regular intervals
These repeating patterns are considered periodic MENDELEEV’S PERIODIC TABLE
Mendeleev’s table grouped elements with similar properties
Mendeleev left many gaps in his periodic table, anticipating that there were undiscovered elements ATOMIC NUMBER
Mendeleev’s Table was very useful, but left two questions unanswered: Why could most elements be arranged in order of increasing atomic mass, but not all? What was the reason for chemical periodicity?
In 1911, English scientist Henry Mosley was examining the emission spectra of many different metals
Mosley noticed that elemental properties aligned better together when they were arranged by atomic number
The periodic law states that the repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements MODERN PERIODIC TABLES
Modern periodic tables arrange elements by both atomic number and chemical 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 group ELECTRON CONFIGURATION AND THE PERIODIC TABLE
Main Idea: The period of an element is determined by its electron configuration. PERIODICITY
Mendeleev’s could not explain why Number Sublevels Period periodicity occurred of in Order Number Elements of Filling However, as unknown elements were 1 2 1s discovered, and more complete periodic tables were made, the 2 8 2s 2p observation of periodicity was more prevalent 3 8 3s 3p 4 18 4s 3d 4p One of the best ways to describe 5 18 5s 4d 5p periodicity is by looking at the number of elements within each period of the 6 32 6s 4f 5d 6p periodic table 7 32 7s 5f 6d 7p s-BLOCK ELEMENTS
Elements in these groups are highly reactive metals
Alkali metals are the elements in Group 1 ns1 configuration Silvery in appearance and very soft Not found in an elemental state in nature
Alkaline-earth metals are the elements in group 2 ns2 configuration Harder, denser and stronger than alkali metals Not found in an elemental state in nature d-BLOCK ELEMENTS
Transition metals are the elements in in the d-block with typical metallic properties ns2(n-1)dx configuration Good conductors of electricity High luster Typically less reactive than alkali metals and alkaline-earth metals p-BLOCK ELEMENTS
Main-group elements are all elements within the s-block and p- block
The properties of groups within the p-block are varied and not necessarily shared by all elements within the group p-BLOCK ELEMENTS
Halogens are the elements in Group 17 ns2np5 configuration Highly-reactive non-metals, reacting vigorously with metals to form salts
Noble gasses are the elements in Group 18 ns2np6 configuration Totally unreactive p-BLOCK ELEMENTS
Metalloids are in the p-block Semiconducting elements Brittle elements with properties of both metals and nonmetals
Post-transition metals are similar to s-block metals Soft and less dense than d-block metals Only found in nature within compounds, but stable in air as pure elements f-BLOCK ELEMENTS
Consists of lanthanides and actinides
ns2(n-1)d1(n-2)fx configuration
Lanthanides are very similar to Group 2 metals Soft and shiny Very reactive
Actinides are all radioactive elements Only the first four actinides have been found naturally on earth NOTABLE GROUPS
Noble Gases Between 1894 and 1900, all the noble gasses were discovered by a variety of scientists These elements had been previously undiscovered since they are totally unreactive
Lanthanides are the 14 elements with atomic numbers from 58 (cerium) to 71 (lutetium)
Actinides are the 14 elements with atomic numbers from 90 (thorium) to 103 (lawrencium)
Elements in the lanthanides and actinides have very similar properties to each other , but were very difficult to identify and place into the periodic table MAJOR GROUPS OF THE PERIODIC TABLE Alkali Metals Alkaline Earth Metals Transition Metals Post- Transition Metals Metalloids Non-Metals Halogens Noble Gases Lanthinides Actinides MAJOR GROUPS OF THE PERIODIC TABLE
Alkali Metals Group 1 Alkaline Earth Metals Group 2 Transition Metals Groups 3-12, with additional metals in groups 13-16 Metaloids Specific metals between metals and non-metals moving diagonally from the top of group 13 to the bottom of group 17 Non-Metals Mostthe remaining elements to the right of netalloids Noble Gases Group 18 Lanthinides Top row of elements removed from period 6 Actinides Bottom row of elements removed from period 7