The Periodic Table The Beginning

In the late 1800’s, Dmitri Mendeleev, a Russian chemist, searched for a way to organize the elements. When he arranged all the elements know at the time in order of increasing atomic masses, he discovered a pattern.

In the periodic table, the elements are arranged by increasing atomic number and by changes in physical and chemical properties.

Mendeleev Mendeleev had to leave blank spaces in his periodic table to keep the elements properly lined up according to their chemical properties. From this information, he was able to predict the properties and mass number of new elements that had not yet been discovered . Two elements that he predicted about were gallium and scandium.

Gallium Gallium wasn’t physically discovered till after Mendeleev's death, but Mendeleev did predict that it was there even though he never saw it.

The Improvement In 1913, the work of Henry G.J. Mosley led to the arrangement of elements based on their increasing atomic numbers instead of an arrangement based on the atomic mass. Reason – Cobalt/Nickel – The mass decreases from left to right while the atomic number increases. Why? – Fewer Neutrons in Nickel that cobalt.

What we use today This is the current method that we use today; increasing atomic number from right to left.

The Atom and the periodic Table Objects often are sorted or grouped according to the properties they have in common. The vertical columns in the periodic table are called groups or families. Groups are numbered 1-18 at the top of the periodic table. Elements in each group have similar properties.

Group 1 This family has all the same properties. Group 1 has only one valence electron in the outer shell. Look at Group 11. They are all shiny metals and conduct electricity. (same properties) (same number of valence electrons.)

Electron Cloud Structure In a neutral atom, the number of protons equals (=) the number of electrons. Scientists have found that electrons within the electron cloud have different amounts of energy. We make models of the electrons by placing the electrons in energy levels

Energy Levels Energy levels nearer the nucleus have lower energy than those levels that are father away.

Valance Electrons Elements in the same group have the same number of electrons in their outer energy level. It is the number of electrons in the outer energy level that determines the chemical properties of the element.

Energy Levels There are 7 energy levels. Energy level 1 can only contain 2 electrons Energy level 2 can only contain 8 electrons. Energy level 3 can only contain 18 electrons. Energy level 4 can only contain 32 electrons. A complete and stable outer energy level will contain 8 electrons.

Rows Rows, also know as periods, move in a horizontal direction. As you move from right to left on the periodic table, each element will add an electron to the outermost level until it reaches its capacity and stars over on a new energy level.

Electron Dot Diagram An electron dot diagram uses the symbol of the element and dots to represent the electrons in their outer energy level. Electron dot diagrams are used also to show hoe the electrons in the outer energy level are bonded when element combine to form compounds.

Example: Hydrogen atom as 1 valence electron. A Fluorine atom has 7 valence electrons

Give the following electron dot diagrams. Na Pb Ne Xe C N O F Notices what happens as you move across the periodic table .

Same Group – Similar Properties The elements in Group 17, the halogens, have electron dot diagrams similar to chlorine. Cl All halogens have seven electron in their outer energy level, all group members will undergo chemical reactions in similar ways.

Let’s come together! A common property of halogens is the ability to form compounds with elements in group 1. Na Cl Na Cl

Not all element will combine with other elements. The elements in Group 18 – the Noble Gases The elements in Group 18 have completed outer energy levels. This special configuration makes Group 18 relatively unreactive.

Group 18 Elements He - Ne - Ar - Kr - Xe - Rn - Write the correct name for the element. He - Ne - Ar - Kr - Xe - Rn -

Regions of the Periodic Table The periodic table has several regions with specific names. The horizontal rows of elements on the periodic table are called Periods (The number of energy levels)

The Periodic Table is broken down into 3 parts. Metals – (largest portion) ( mainly left side and middle) (75%) Non-Metals – (gases) (Right side) (18%) Metalloids – (smallest group) (semimetals) Located between metals and nonmetals.

Elements in the Universe Are all of the elements throughout the universe the same? Using the technology that is available today, scientists are finding the same elements throughout the universe. 98% of the universe is made of hydrogen