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The Periodic Table. Development of the Periodic Table. There were only 23 at the time Most were known since prehistoric times Examples include gold, silver, carbon and oxygen. Late 1790s- Antoine Lavoisier made a list of all the known elements.
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Development of the Periodic Table • There were only 23 at the time • Most were known since prehistoric times • Examples include gold, silver, carbon and oxygen Late 1790s- Antoine Lavoisier made a list of all the known elements
As technology evolved, more elements were found. • By 1870, there were 70 known elements • John Newlands noticed that when elements were arranged by increasing atomic mass, every eighth element has similar properties. • Newlands had the right idea, but his arrangement didn’t work for every element.
In 1869, Dmitri Mendeleev proposed the first periodic table. • His periodic table was arranged in order of increasing atomic mass and also had elements with similar properties in the same column. • He left blanks for elements that had not been discovered, but he predicted would exist. • Some examples are scandium, gallium, and germanium
Mendeleev’s table had some of the elements in the wrong order. • Cobalt has a higher mass than nickel, but should come before nickel on the periodic table • Since atomic mass isn’t the right way to arrange the elements, what should they be arranged by?
In 1913, English chemist Henry Moseley determined what the problem was. • The error was arranging the table by increasing atomic mass. It should be arranged by increasing atomic number. • The statement that there is periodic repetition of properties when they are arranged by increasing atomic number is called the periodic law.
The columns on the periodic table are called groups (tell you the number of valance electrons). • The rows are called periods (tell you the number of electron shells). • What group and period are carbon and tungsten in?
Metals. Vs. Non-Metals MetalsNon-Metals good conductors poor conductors have luster lack luster high density low density high melting point low melting point malleable not malleable ductile not ductile lose e- gain e- corrode easily brittle Metalloids are elements that have chemical and physical properties of metals and non-metals. They are located on the stair-step line.
Group Names • Group 1: Alkali Metals • Group 2: Alkaline Earth Metals • Group 3 – 12: Transition Metals • Group 13: Boron Group • Group 14: Carbon Group • Group 15: Nitrogen Group • Group 16: Oxygen Group • Group 17: Halogens • Group 18: Noble Gases
Alkali Metals • Found in group 1 or 1A • The most reactive metals • Explode on contact with air or water • Increase in reactivity as you go down the group • Soft enough to cut with a knife
Alkaline Earth Metals • Found in group 2 or 2A • Also very reactive metals, but less so • Increase in reactivity as you go down the group • Harder than the Alkali metals
Transition Metals • Found in the depressed area of the periodic table (Groups 3-12 or the B columns) • Make up the largest portion of the periodic table • Tend to be stable
Halogens • Found in group 17 or 7A • Another very reactive group of elements – the most reactive nonmetals
Noble Gases • Found in group 18 or 8A • Most stable group of elements because they have a full valance shell
