The Periodic Table Chemistry 11

The Periodic Table’s History: We didn’t always have the periodic table! by 1817, chemists had discovered 52 elements by 1863 that number had risen to 62 Chemists needed a way to organize the elements

William Odling: 1857 Found elements could be divided into 13 groups based on chemical and physical properties

John Newlands (1863-1866): Assigned hydrogen an arbitrary mass of 1 and ordered elements by their mass Found every eighth element shared a common set of properties (the law of octaves) Very elegant model, but did not allow for prediction of new elements Problem: every time new elements were discovered, the table had to be rearranged

Dimitri Mendeleev (1869): Russian chemist Organized the elements according to their masses and properties. When he did this, he discovered that certain properties recur PERIODICALLY (like Newlands) Some properties didn’t line up, so… …he left gaps in his table for elements he proposed had not yet been discovered

This new periodic table allowed chemists to: Organize and understand their data Predict new properties of elements

Henry Mosley (1887-1915): developed the modern table in 1911 and developed the Periodic Law Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers Plain English: When elements are arranged in order of increasing atomic number, similar properties appear at regular intervals

What Stayed the Same? What Changed? Elements are still grouped by properties Similar properties are still in the same column What Changed? Order is by increasing atomic number Added a column of elements Mendeleev didn’t know about

The Modern Periodic Table: The table we see today wasn’t actually “finished” until the early 1900’s. Strutt and Dorn added the Noble Gases in 1894 The Lanthanides and Actinides were added in the middle of the 1900’s Still changes being made today, there are always discoveries yet to be made!

Major Divisions of the Periodic Table The set of elements in a given row going across the table. Group or Family: The set of elements in a given column going up and down the table.

Families of the Periodic Table:

Metals, Non-metals and Semi-metals We can classify elements according to their metallic character The Properties of Metals: Reflect light when polished (lustrous) Are opaque Are good conductors of electricity or heat Generally, but not always, flexible when in thin sheets Generally malleable (can be hammered into thin sheets Generally ductile (can be stretched into wires) Usually solid at room temperatures (Hg is an exception). React with acids

The Properties of Non-Metals: Are gasses, liquids, or brittle solids at room temperature Are poor heat and electricity conductors If solids, are dull to lustrous in appearance and opaque to translucent

Semi-metals / Semi-conductors: Some elements share properties from both metals and non-metals Semiconductor: A non-metal having an electrical conductivity which increases with temperature A couple of important notes: Semiconductors were formally called “Metalloids” The important difference between metals and semiconductors is that conductivity decreases with an increase in temperature for metals.

Trends on the Periodic Table: The elements change from METALIC to NON-METALIC going from LEFT to RIGHT across the periodic table The elements become MORE METALIC (or better metals) going DOWN a family on the periodic table

Alkali Metals: Families of the Periodic Table “group 1” soft, silver coloured metals React violently with water react with air form ions with charges of 1+ http://www.youtube.com/watch?v=m55kgyApYrY

Alkaline-Earth Metals: “group 2” reactive metals form ions with charges of 2+ react with air (oxidize) – ex. MgO

Transition Metals: vary greatly in chemical properties many have multiple possible ion charges usually form colourful compounds

Lanthanides / Actinides: Part of the Transition metals found at the bottom of the periodic table varying chemical properties some elements are synthetic (not naturally occurring)

Halogens: “group 17” extremely reactive form ions with charges of 1‑ form acids with hydrogen (ex. HCl)

Noble Gases: Assignment: “group 18” low reactivity (virtually unreactive) Assignment: Periodic Table Worksheet