The Periodic Table

1. The Periodic Table

2. Review of the atom • Atoms contain protons and neutrons in the nucleus • Electrons are found outside the nucleus

3. The Periodic Table – A History • The Periodic Table was created in the late 1800’s by Dmitri Mendeleev. • He arranged the elements in order of increasing atomic mass. • When this was done, there was a repeating pattern of chemical properties. • Using his chart, Mendeleev was able to predict elements that were unknown at the time and their chemical properties.

4. The Periodic Table

5. The Elements • Elements are substances that contain only one type of atom. • On the periodic table they are represented with a one or two letter symbol. • The first letter of the symbol is always capitalized. If there is a second it is not capitalized.

6. What is the Atomic Number? • An element is defined by the number of protons in it’s nucleus. • The number of protons is the atomic number of an element. • The atomic number is located in the top of a cell on the table and is always a whole number.

7. What is the Atomic Mass? • Protons and neutrons mass 1.6726 x 10-24 g • Since this number is so small scientists created the atomic mass unit (amu) to describe the mass of atoms. • 1 amu = 1.6726 x 10-24 g

8. Atomic Mass • The mass number of an atom is the number of protons and neutrons in the nucleus • If you know the mass number and the atomic number, you can calculate the number of neutrons in an atom. • # neutrons = mass number – atomic number

9. Isotopes • Not all atoms of an element have the same number of neutrons. • An isotope of an element is one that has a different number of neutrons.

10. Atomic Mass on the Periodic Table • On the periodic table the weighted average mass of all isotopes of an element is displayed at the bottom of a cell. • A weighted average is taking a sample and finding how common each isotope of an element is and averaging those masses together.

11. Metals and Nonmetals • Elements on the periodic table are divided into metals and nonmetals. • The stair step on the right of table is the dividing line between metals and nonmetals, except for hydrogen. • Anything along the line is a metalloid except for aluminum. • Metalloids display properties of both metals and nonmetals

12. Groups on the Periodic Table • Columns on the periodic table are called groups. They have a roman numeral or a number at the top. • All elements in a group share similar chemical properties. • All elements in a group usually share the same number of electrons in their outer energy level • Elements going horizontally on the table are called periods.

13. Electron Structure • Outer energy level electrons are what determines how a substance reacts chemically • All atoms want to have eight electrons in their outer shell. • Elements with eight electrons in their outer shell do not react under normal circumstances.

14. Electron Dot Diagram • An electron dot diagram is a way to show the electrons in the outer energy level of an element • It consists of the symbol for the element and dots to represent the electrons • To determine the number of electrons, count the group ignoring the transition metals