The Periodic Table Chapter 4, Section 2

It’s ELEMENTary Elements cannot be broken down chemically in to different kinds of matter. Each element has its own unique symbol –Sometimes the symbol is a single capitalized letter –If the symbol consists of more than one letter, the first letter is capitalized and the other letters are lower case. –Usually the symbol is the same as the first letter of the element If it is not, it may be the first letter of the Latin word for the same element. Example – Iron’s symbol is Fe…short for Ferrium If the single letter has already been used, then the second letter is added. Example: Helium – H was used for Hydrogen so Helium’s symbol is He

You must memorize the symbol for elements 1-20 and the following metals: –Mercury –Iron –Copper –Gold –Silver –Zinc

Atomic Number Atomic Number: the number of protons in an element The atomic number is the smaller whole number found next to the element The atomic number never changes – atoms are differentiated by how many protons they have Each element has a different atomic number C

Atomic Mass The atomic mass is the sum of the number of protons and neutrons in an element The atomic mass is the larger number that is NOT a whole number Question: Why aren’t the electrons included in the mass number? C

Calculating the # of Neutrons 1.Take the atomic mass and round it to the nearest whole number 2.Subtract the atomic number from this number Example: Carbon rounds to – 6 =6 neutrons

Isotopes Isotopes contain a different number of neutrons than the normal atom. This will change the atomic mass but the number of protons and electrons remains the same. Example: C is the new mass…14 – 6 = 8 neutrons Element New Mass

Atomic Mass Explained Isotopes explain why the atomic mass is NOT a whole number… The atomic mass is often referred to as the “Average Atomic Mass.” It is an average of all of the isotopes that exist. Chlorine’s Avg. Atomic Mass is – There must be more Cl-35 than Cl-37

Bohr Models The Bohr Model is the easiest way to draw an atom (the solar system model). 1.Draw a nucleus 2.Determine the number of protons and neutrons found in the nucleus and write this number in the nucleus 3.Determine how many electrons there are and place each one in its appropriate energy level P = 6 N = 6 2 4

Let’s Practice Making Bohr Models See the worksheet!

Valence Electrons Valence electrons are the electrons found in the outermost energy level. Example: Carbon has 4 valence electrons

The Periodic Table The periodic table groups similar elements together. This makes it easier to predict properties of an element based on where it is in the periodic table. This is called the periodic law.

Periodic Table Organization Period: horizontal rows –Tells you the number of energy levels found in an element Group/Family: vertical columns –Elements within a group have similar properties and contain the same number of valence electrons –There are 18 groups –Groups 3-12: transition metals –Group 18: inert or noble gases –Group 17: Halogens –Group 1: Hydrogen and the Alkali Metals