Periodicity CHEMISTRY 11 MS. MCGRATH

The First Periodic Law Dmitri Mendeleev discovered the periodic law in 1869 First periodic law – when elements are arranged in order of increasing atomic mass, elements with similar properties recur at regular intervals

The Modern Periodic Law Henry Moseley determined the nuclear charge, aka the atomic number He arranged the elements by order of atomic number

The Modern Periodic Law When elements are arranged in order of increasing atomic number, elements with similar properties occur at regular intervals. The physical and chemical properties of the elements are a periodic function of the atomic number.

Features of the modern periodic table Groups (aka Families) 18 vertical columns containing elements with similar chemical and physical properties Group 1, 2, 13 – 17 constitute the main-group elements Group 1 – alkali metals Group 2 – alkaline earth metals Group 13 – earth metals Group 17 – halogens Group 18 – rare gases, noble gases, inert gases Groups 3 – 12 are called the transition metals

Features of the modern periodic table Periods 7 horizontal rows the first period contains two elements – hydrogen and helium the bottom two rows represent two series – the lanthanide series and the actinide series

Features of the modern periodic table Metals more than ¾ of elements are metals good conductors of heat and electricity characteristic lustre (shine) malleable (can be hammered into sheets) ductile (can be drawn into wires) high densities high melting and boiling points mercury is the only liquid metal at room temperature

Features of the modern periodic table Non-metals do not have lustre brittle non-ductile, non-malleable poor conductors of heat and electricity iodine, phosphorus and carbon are solid non-metals bromine is the only non-metal that is a liquid at room temperature gases such as chlorine, oxygen and helium are non-metals

Features of the modern periodic table Metalloids has properties of metals and non-metals boron, silicon, germanium, arsenic, antimony, tellurium, polonium and astatine fall in this category

Properties Noble Gases all these gases are colorless, odorless, and chemically inert under proper conditions, these gases can combine with very reactive elements such as fluorine

Properties Alkali Metals group 1 chemically active they react vigorously with water to release hydrogen from the water all react with chlorine to colorless compounds which crystalize in cubic shapes and have similar formulas: LiCl, NaCl, KCl, RbCl, CsCl, FrCl

Properties Halogen group 17 the word halogen means “salt-former” they react with hydrogen to form compounds that dissolve in water to make an acidic solution they react with metals to form salts in their natural state, these elements are diatomic: F 2, Cl 2, Br 2, I 2

Properties Hydrogen it is often place in group 1of the periodic table, although it is not a metal it can form compounds with halogens, just as the metals of group 1 it could also be place in group 17 (the halogens) because it can also react with metals, such as sodium, and non-metals, such as nitrogen because of its unique characteristics, hydrogen does not have a definite position on the periodic table – although on most periodic tables it is found in group 1

Metallic trends the most metallic elements are found in group 1 the metallic character of the elements decreases from left to right in a row and increases from top to bottom in a group francium is the most metallic element in the periodic table

Non-metallic trends the most non-metallic elements are in group 17 there is a gradual transition from metallic to non-metallic properties as one goes from left to right within a period fluorine is the least metallic element (or the most non-metallic element) in the periodic table