1. Patterns  Patterns exist everywhere –. They occur in regular occurring shapes & structures and in repeating events &  relationships.  Scientists seek explanations for observed patterns and for the similarity and diversity within them.

2. Dmitri Mendeleev Father of Periodic Table Dmitri Mendeleev Father of Periodic Table  In 1869, Dmitri Mendeleev decided on a plan to organize the elements.  He wrote facts about all of the known elements on paper cards.  He included information about the elements physical and chemical properties.  He looked for clues about how those elements compared to each other.  He studied the patterns of the elements.  He was able to organize the elements at the time in order of their atomic mass.  He realized that the physical and chemical properties of elements were related to their atomic mass in a ‘periodic’ way. He arranged them so that groups of elements with similar properties fell into vertical columns in his table. For many years scientists had been struggling to come up with patterns in the elements. Elements are a substance that cannot be broken down. Mendeleev was creating his table before the time when detailed discoveries about the atom had been conducted.

3. Mendeleev’s Periodic Tables The table at the left wasThe table at the right was Mendeleev’s first sketch the table that Mendeleev Mendeleev’s first sketch the table that Mendeleev Of the periodic table.published in 1869. Notice the gaps that he was not able to fill in. He predicted the atomic mass of new elements that would later be found!

4. Alien Periodic Table Horizontal Patterns: *Number of fingers increased by one. *The body shape was all the same. *They all had their first four fingers on their left hand. When there was more than four fingers, they had a right arm and hand. Vertical Patterns: *They had a characteristic that grew by one. (horns, hair, foot length, stripes, hat, hair length, tufts, number or legs) *They all had the same number of fingers. * Body shape progressed from triangle to circle to rectangle to oval to upside-down triangle.

5. Current Periodic Table  The table is organized from top to bottom and left to right by the number of protons.  The table is organized from top to bottom and left to right by the atomic mass.

6. Groups and Periods  18 vertical columns called GROUPS or FAMILIES Elements in each group have similar characteristics. Elements in each group have similar characteristics. Elements share similar physical and chemical properties. Elements share similar physical and chemical properties.  7 horizontal rows called PERIODS Series of different elements that are not alike but they have progressive patterns. Series of different elements that are not alike but they have progressive patterns. Pattern from left to right is reactive to non- reactive. Pattern from left to right is reactive to non- reactive.

7. Physical Properties of the Periodic Table Group two elements are known as the alkaline earth metals. They are all silver-colored and soft, and have relatively low densities, melting points, and boiling points. densities melting pointsboiling pointsdensities melting pointsboiling points

8. Chemical Properties of the Periodic Table Group 17 elements are called halogens. They are extremely reactive. Due to their e high reactivity (electronegativity), they are not found in their elemental form in any natural environment on Earth. They are generally toxic, or even lethal, to biological organisms in their elemental forms.

9. *The number of the period indicates how many electron orbitals there are in each atom. *As you move across the period, the number of electrons in the outermost orbital increases by one. *In a group, the outermost orbital has the same number of electrons. *Because electrons are the outermost particles in an atom, they are the ones that give an atom it’s properties, so elements with similar outer orbitals, have similar properties

10. Group 1 - Has one outside electrons. They are very reactive metals that react violently with water. Group 2 – Have two outside electrons. They are soft, silver metals that are reactive with oxygen. Group 17 – Have 7 outside electrons. They are very reactive nonmetals. Group 18 – Have 8 outside electrons. They are very nonreactive gases. (noble gases)