The Periodic Table

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

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.

The Periodic Table

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.

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.

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

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

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.

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.

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

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.

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.

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