Unit 2 lecture 2- Periodic Table Intro Why do we have a Periodic Table of Elements?

Quick Tour of the periodic table

History of the Periodic Table 1829: Dobereiner arranged the elements by mass and identified the halogens (group 7) and noble gases (group 8) 1864: Newlands noticed property patterns and reported the law of octaves (8) 1869: Meyer noticed a relationship between properties and atomic mass 1896: Dmitri Mendeleev (father of the periodic table) arranged elements by atomic mass and properties 1914: Henry Moseley arranged the elements by their atomic number and properties SUMMARY: First was arranged by ATOMIC MASS, then by ATOMIC NUMBER and PROPERTIES

Organizing groups by common properties

The periodic table tells us about the elements Find the Key on your periodic table (it uses sodium)

Periods and Groups 7 PERIODS - horizontal rows 18 GROUPS (families)- vertical columns whose elements have similar properties. There are 8 major groups (1A to 8A)

Transition metals, Lanthanides, and Actinides

Metals (blue), Nonmetals (yellow), metalloids (pink)

Metals Conductors of heat and electricity On the left side of staircase (most of the elements!) As you move further to the left and down, there is more metallic character Conductors of heat and electricity Malleable (can be hammered into thin sheets) Ductile (can be pulled into wires) Lustrous (shiny) Example: Gold

Nonmetals Found on the right side of the staircase. As you move to the right and up, there is more non-metallic character. Low boiling points, brittle, dull, good insulators Example: Sulfur

Metalloids/semimetals - Found along the staircase. Have properties of metals and non-metals Tend to be good semiconductors in transistors. Example: Silicon

Metallic and non-metallic character

Groups with Special Names: Group 1 (1A) Alkali Metals – soft metals that are extremely reactive. Group 2 (2A) Alkali Earth Metals – shiny reactive metals -Group 17 (7A) Halogens - Extremely reactive nonmetals - Group 18 (8A) Noble Gases - Inert gases (unreactive with other elements).

Other Information from the periodic table

Ionization The energy needed to remove one or more electrons from a neutral atom to form a positively charged ion is a physical property that influences the chemical behavior of the atom. So how easy would it be for another element to take another elements electrons. This is important property when atoms bond to form compounds. It defines which elements can join with which other elements and how many atoms.

Electronegativity Electronegativity is a measure of an atom's ability to attract the shared electrons in a bond. If atoms bonded together have the same electronegativity, the shared electrons will be equally shared. If they are different they share unequally and the more different they are the more unequally they share.

Borh’s Models

Atomic Radius The atomic radius of a chemical element is a measure of the size of its atoms, usually the mean or typical distance from the center of the nucleus to the boundary of the surrounding cloud of electrons. So the higher the radius the bigger the atom.