The Periodic Table Chapter 6 Notes
History of the PT Dobereiner –German Chemist –Proposed “triads” in 1829: grouping of 3 elements with similar properties –Observed that melting point decreased and density increased as the atomic mass of an element increased
Mendeleev –Russian Chemist –Published a table of elements in 1869 in which the elements were organized by increasing atomic mass –First periodic table to use rows and columns –Left “missing spots” for elements not yet discovered –Tellurium (mass = 128) and Iodine (mass = 127) were in the wrong order – thought the masses were wrong
Mendeleev’s Periodic Table
The Modern PT Very similar to the periodic table developed by Mendeleev Organized by horizontal rows (called periods) and vertical columns (called groups or families) Shows a pattern of physical and chemical properties Uses atomic number to order elements, NOT atomic mass
The Modern Periodic Table
Within a Group on the PT: The number of valence electrons (outermost electrons) = the group number
Because the number of valence electrons within a group are the same, elements within a group have similar physical and chemical properties For example, what happens when an alkali metal comes into contact with water?what happens when an alkali metal comes into contact with water? Alkali metals react violently with water to form hydrogen gas and release a lot of energy!
Classification of Elements Metals –Have luster (shine) –Conduct heat and electricity –Malleable (can bend without breaking) –Solids (except for mercury) –High melting points –Groups 1A, 2A and all of Group B Group B – Transition Metals Bottom 2 Rows – Inner Transition Metals –Lanthanides – top row –Actinides – bottom row (also called the Rare Earth Metals)
Classification of Elements Nonmetals –Do not conduct heat or electricity –Are brittle –Many are gases at room temperature –Do not have luster –Lower melting points –Located in Groups 3A – 8A
Classification of Elements Metalloids –Have some properties of metals and other properties of nonmetals depending on the conditions the element is under (temperature, pressure, etc.) –Border the metals and nonmetals on the periodic table –Semiconductors: conduct electricity better than a nonmetal but not as well as a metal
Group Characteristics Representative Elements –A–All Group A elements –R–Represent the entire spectrum of element characteristics Metals Nonmetals Metalloids Solids Liquids Gases
Transition Elements –A–All Group B elements –S–Show a gradual transition in properties from metals to nonmetals Inner Transition Elements –“–“f block” –L–Lanthanides – top row –A–Actinides – bottom row
Alkali Metals Group 1A All have one valence electron All end in the electron configuration s 1 Soft, silvery white metals Good conductors of heat and electricity Very reactive
Alkaline Earth Metals Group 2A All have 2 valence electrons All end in the electron configuration s 2 Less reactive than the alkali metals More dense, harder, and have a higher melting point
Boron Group Group 3A All have 3 valence electrons All end in the electron configuration s 2 p 1 Not very reactive Silvery, fairly soft, and good conductors of heat and electricity
Carbon Group Group 4A All have 4 valence electrons All end in the electron configuration s 2 p 2 Form bonds by sharing electrons Mixture of metals, nonmetals, and metalloids
Nitrogen Group Group 5A All have 5 valence electrons All end in the electron configuration s 2 p 3 Nonmetals and metalloids
Chalcogens Group 6A All have 6 valence electrons All end in the electron configuration s 2 p 4 Nonmetals and metalloids Very reactive
Halogens Group 7A All have 7 valence electrons All end in the electron configuration s 2 p 5 All are nonmetals Exist as diatomic molecules – two atoms of the same element bonded together (Cl 2, F 2 ) Very reactive
Noble Gases Group 8A All have 8 valence electrons (except for Helium which has 2 valence electrons) All end in the electron configuration s 2 p 6 All are gases All have a full outer shell which causes them to be unreactive (previously called inert)