PERIODIC TABLE I

INTRODUCTION Open just about any chemistry book and you will see a copy of the periodic table of the elements. The periodic table is a framework for classifying information about the properties of all known elements on Earth.

INTRODUCTION The grid-like structure is used to organize the elements according to their properties. The rows and columns tell specific information about the elements as does each box that represents an element.

INTRODUCTION We will take a brief look at the history and development of the table, and then examine the element cells, the structure of the table, and the reasons why the table is a useful tool for chemists and other scientists.

INTRODUCTION Before written history, people were aware of some of the elements in the periodic table. The first pure elements had been known since the time of the Ancient Greeks, who used the metallic elements such as gold (Au), silver (Ag), copper (Cu), lead, (Pb), tin (Sn), and mercury (Hg).

INTRODUCTION Between 1649 and 1869, the amount of knowledge about properties of elements and their compounds was added to by many scientists and chemists.

INTRODUCTION Hennig Brand, a German scientist, who discovered phosphorus (P) in 1649. French chemist, Antoine Lavoisier who in 1739 drew a table that contained 33 known elements at that time.

INTRODUCTION In 1863 John Newlands, an English chemist, wrote a paper which organized the 53 known elements into 11 categories. German chemist Lothar Meyer who produced a periodic table in 1869.

INTRODUCTION By 1869, 63 elements had been discovered. A Russian scientist, Dmitri Mendeleev discovered a set of patterns that applied to all the elements.

INTRODUCTION Mendeleev knew that some elements have similar chemical and physical properties. Mendeleev thought that these properties were clues to a hidden pattern. He noticed that when he arranged the elements according to their atomic mass the properties of the elements repeated.

INTRODUCTION By arranging his cards into groups where all the elements shared properties, he noticed that there were blank spaces in the table. He predicted that the unknown elements that fit those spaces had yet to be discovered.

INTRODUCTION Mendeleev was correct.

INTRODUCTION Mendeleev is considered to be the father of the periodic table.

INTRODUCTION In 1913 Henry Moseley found a way to measure the positive charge of an atom, the atomic number, so the table was rearranged by atomic number, not mass. As a result, some elements were shifted and the patterns of the table became even stronger.

INTRODUCTION Each element on the periodic table is represented by a chemical symbol. These symbols are shown along with other vital information in a cell on the periodic table.

INTRODUCTION 8 represents the atomic number. O represents chemical symbol 15.99 represents atomic mass

INTRODUCTION The cells are arranged on the table in order of their atomic number. Each cell as you move from left to right increases by one proton, so hydrogen which is atomic number 1 has 1 proton, helium has 2 protons, lithium has 3 protons and so on. Atomic number

INTRODUCTION The atomic number which represents the number of protons is also the number of electrons for each atom. In order for an atom to be stable, in other words it so it doesn’t just fall apart, the protons and electrons must balance each other.

INTRODUCTION The information from the table can also be used to help determine the number of neutrons in an element.

INTRODUCTION Once you know the atomic number of the element and its atomic mass you simply subtract to find the number of neutrons.

INTRODUCTION Let’s take the element aluminum which has a mass of 26.98, round that to a whole number, 27, then subtract its atomic number 13 from that. What did you get? If you got 14 then you are correct. Aluminum has 14 neutrons in its nucleus.

INTRODUCTION The names of the elements and their symbols also follow some rules. Element symbols are always 1, 2 or 3 letters. The first letter is always a capital, the 2nd and 3rd letter are always lower case.

INTRODUCTION You may have noticed that not all the elements have symbols that seem to match their names. Sometimes symbols are used that represent the Latin names. For example lead is Pb, which is Latin for Plumbum. Tell the story of lead.

INTRODUCTION Many of the names of elements are given for the scientists who discovered them, some are named for cities, countries, famous scientists, or even gods.

OBJECTIVE Learn the rules for the rows and columns of the periodic table. Learn the rules for the cells of the periodic table.

VOCABULARY Periods – horizontal rows of the table. Groups – vertical columns of the table. Periodically – happening with regular occurrence.

IN ACTIVITY Si He Ne Md Na Re Use the periodic table in the back of your student agenda to find the chemical symbols for these elements. #14 #2 #10 #101 #11 #75 Si He Ne Md Na Re

NOTES Dmitri Mendeleev considered to be the father of the periodic table. Published his table in 1869. Arranged his table by atomic mass. Predicted the existence of unknown elements in his table.

NOTES Henry Moseley arranged the table according to atomic number in 1913. Some elements shifted because of this. The modern periodic table uses Moseley’s method of organization.

NOTES Each element has its own cell on the table. Most periodic tables include the symbol, the atomic number, and the atomic mass. Other info is sometimes added to the cells.

NOTES Atomic number – represents the number of protons and electrons in the atom. Chemical symbol Atomic mass – the average mass of the protons and neutrons in the nucleus of the atom.

NOTES Elements are named for cities, countries, famous scientists, or for Latin names. Symbols are always capitalized followed by lower case letters.

OUT QUESTION Calculate the neutrons for these elements. 1. Atomic number 22, atomic mass 47.87 2. Atomic number 48, atomic mass 112.41 26 64