Stand by for an introduction to Atoms and The Periodic Table

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Current element count: 118 Total Elements 95 naturally occurring 20 + others Currently up to #118, as of 1/28/08

A look at the development of the Periodic Table through history

Dimitri Mendeleeve, Russian, Johann Dobereiner, German, John Newlands, Englishman, Both noticed that there was a relationship between atomic mass & chemical behavior. First periodic table of elements produced in 1869.

Dobereiner grouped elements in groups of 3 based on similarities. Calcium (mass, 40), strontium (mass 88), and barium (mass 137) possess similar chemical properties.

Dobereiner noticed the masses of strontium fell midway between the masses of calcium and barium: Ca Sr Ba ( ) ÷ 2 = Dobereiner noticed the masses of strontium fell midway between the masses of calcium and barium: Ca Sr Ba ( ) ÷ 2 =

Dobereiner noticed the same pattern for 2 groups: 3 alkali metals: (Li/Na/K) and 3 halogens (Cl/Br/I). Dobereiner noticed the same pattern for 2 groups: 3 alkali metals: (Li/Na/K) and 3 halogens (Cl/Br/I). Li Na K Cl Br I

Dobereiner proposed the Law of Triads: The Middle element in the group of 3 (triad) had a mass that was the average of the other two. Soon other scientists found chemical relationships extended beyond triads. As a result of Dobereiner’s work: Fluorine was added to Cl/Br/I group, sulfur, oxygen, selenium and tellurium were grouped into a family, nitrogen, phosphorus, arsenic, antimony, & bismuth were classified as another group.

John Newlands, having arranged the 62 known elements in order of increasing atomic mass, noted that after an interval of eight elements, similar physical/chemical properties reappeared. Newlands was the first to formulate the concept of periodicity in the properties of the chemical elements.. In 1863 he wrote a paper proposing the Law of Octaves: Elements exhibit similar behavior to the eighth element following it in the table

Newlands’ “Octave” Periodic Table Newlands’ “Octave” Periodic Table

The name of the table was taken from Periodic Law which stated that an atoms’ behavior could be predicted by its mass. Mendeleeve arranged the elements in his first periodic table by their increasing atomic mass and left blank spaces where he believed elements not yet discovered should be placed.

One form of Mendeleev's periodic table, from the 1st English edition of his textbook

As time passed, scientists made an effort to improve the Table. It was first improved by a brilliant English physicist, Henry Moseley in Moseley performed many tests that led him to the conclusion that the elements should be arranged by increasing atomic number, not mass as was originally proposed.

By changing the Periodic Table to reflect this new belief, this meant changing the Periodic Law. So, Moseley created the Modern Periodic Law, which stated that the chemical and physical properties to the elements are periodic functions of their atomic numbers. During WW II, Moseley was killed in action. As new elements were discovered through the early 1900's and 1920's they were added to the Periodic Table.

AtomsAtoms A t o m s nd he he Peri dic Peri dic Table Table How do they relate?

“It’s elementary, my dear Watson”. Au Gold Let’s look at all the “stuff” inside each of the boxes of the Periodic Table & see what can be learned about the element found there.

. Au The Chemical Symbol Gold is the Anglo- Saxon name given to the metal and it comes from the Latin word “Aurum” which means gold. Gold

Au The Atomic Number The atomic number for Gold is 79. This number not only denotes the elements’ position in the Periodic Table, but it also indicates the number of protons and electrons found within the atom. Gold 79 All elements as listed in the P.T. are considered neutral & have No Charge.

Au The Atomic Mass The atomic mass is an average of all known isotopes of that element found to exist. Gold This average is called a weighted average and is based on the number of isotopes present and their percent abundance.

The Atomic Mass (avg.) Au Gold To determine the Avg. atomic mass let’s use the following example: Let’s say there are 5 isotopes of Gold with the following masses and abundances: Au-197 (50%) Au-195 (28%) Au-194(10%) Au-193(9%) Au-199(3%) Au-197 would have the greatest effect on the average because it is more prevalent than Au-199. That is why the average atomic mass is called a weighted average.

Au The Atomic Mass The Atomic Mass, is also known as the Average Atomic Mass. For gold it is Gold Mass # = Avg. Atomic Mass rounded The number of neutrons within the atom’s nucleus can be determined by subtracting the atomic number from the mass number. 197 amu

The Arrangement of the Periodic Table

The Periodic Table is organized into horizontal rows and vertical columns. Each horizontal row is called a period. There are seven periods, numbered 1 to 7. And each vertical column is called a group or family. There are 18 groups, numbered 1 to 18. Each element’s box contains numbers and a symbol describing the element in full detail.

The arrangement of the Periodic Table The arrangement of the Periodic Table Family Family Period Period A vertical column A vertical column A horizontal row. A horizontal row.

The arrangement of the Periodic Table Family Family A vertical column A vertical column Periodic Law states that when elements are arranged in order of increasing atomic number their physical and chemical properties show a periodic pattern. Families are elements that have similar properties.

The arrangement of the Periodic Table Period Period A horizontal row. Periods are horizontal rows in the periodic table. As you move from left to right in the table, non-metallic properties and atomic mass increases for each element.

Please get out your professionally printed copy and use it as a reference as we begin to analyze the information contained and the trends found within the Periodic Table. I’m going to pass out to you the words to a song called The Elements. This song was written by Tom Lehrer &describes the elements found in the Periodic Table at the time the song Try to sing or say the element names along with the song, If you think you can keep up!

The Families of the Periodic Table

110 U un 111 U uu 112 U ub The Alkali Metals

110 U un 111 U uu 112 U ub The Alkaline Earth Metals

110 U un 111 U uu 112 U ub The Boron Family

110 U un 111 U uu 112 U ub The Carbon Family

110 U un 111 U uu 112 U ub The Nitrogen Family

110 U un 111 U uu 112 U ub The Oxygen Family

110 U un 111 U uu 112 U ub The Halogens

110 U un 111 U uu 112 U ub The Inert or “Noble” Gases

110 U un 111 U uu 112 U ub The Lanthanide Series

110 U un 111 U uu 112 U ub The Actinide Series Transition Metals

110 U un 111 U uu 112 U ub Metals Nonmetals

Using the blank Periodic Table, which will be handed out to you, we will make a color coded chart showing the different Families, Trends, and other valuable information found there. This information will help you to draw better conclusions during future labs & activities we will do during the remainder of the year.

The following information should be placed on your table: The Alkali Metals The Alkaline Earth Metals The Boron Family The Carbon Family The Nitrogen Family The Oxygen Family The Halogens The Inert or Nobel Gases Number Families 1-18 Give Families 1A-8A an additional number above the family column. Lanthanide Series Actinide Series The Transition Metals The Metalloids, metals & nonmetals

Your finished table should resemble this one Non-metals Metals Metalloids (semi-metals) A2A 3A4A 5A6A 7A 8A