The Periodic Table

Many chemicals have very similar colours, lustre, and conductivity of electricity and heat. Scientists were able to classify only two groups of elements at this point: metals and non-metals.

MENDELEEV AND THE FIRST PERIODIC TABLE A Russian scientist named Dmitri Mendeleev came up with a way to organize the elements and it’s a system we still use today. He found that certain elements had very similar physical and chemical properties. He kept finding that certain elements could be grouped into categories based on their properties.

He took elements with similar properties and placed them into vertical columns. Unlike scientists before him, he didn’t just use the atomic mass number to sort the elements. Mendeleev’s table even had spaces in it for elements that had not yet been discovered. As scientists discovered more elements, they found that the new elements fit perfectly into the spaces left by Mendeleev.

TODAY’S PERIODIC TABLE As more was discovered about chemistry and elements, they discovered that the most important number about elements is not the atomic mass number. The most important number is the atomic number (which tells us how many protons and electrons are in an atom). Let’s now look at the periodic table and see what patterns exist:

Everything to the left of the “staircase” is a metal Everything to the left of the “staircase” is a metal. Most metals are solids at room temperature. Everything to the right of the staircase is a non-metal. Most non-metals are gases and liquids at room temperature. The vertical (up and down) columns are called “groups”. There are 18 groups on the periodic table.

Alkali Metals Group 1 elements are called the Alkali Metals. Every element in this group is very reactive. These elements will light on fire when placed in water!

Alkaline Earth Metals. Group 2 elements are called the Alkaline Earth Metals. These elements are also very reactive.

Halogens Group 17 elements are called the Halogens. This group is also very reactive, however, they all exist as diatomic molecules (for example, chlorine exists as Cl2) and are therefore not as reactive.

Noble Gases Group 18 elements are called the Noble Gases. These elements are all unreactive and exist as gases.

The horizontal (across) columns are called “periods The horizontal (across) columns are called “periods.” There are 7 periods on the periodic table All of the elements from group 3 to the staircase are called “transition metals.” The transition metals include most of the metals you are familiar with such as gold, lead, copper, and tin.

Video http://www.youtube.com/watch?v=Ft4E1eCUItI

Homework Complete the subatomic particle worksheet Complete AIM 3