Classification of Elements: The Periodic Table Chapter 6 Classification of Elements: The Periodic Table

How were the Elements Organized and Arranged into the First Periodic Table? Dmitri Mendeleev – Russian chemist from the Mid 1800’s He took all of the info that was collected about the 63 known elements and wrote in on cards The properties that he wrote down were both physical (atomic mass, color, density, melting point) and chemical (reactivity and atomic bonding) The bonding data is called valence number – this means how many electrons an atom will lose, gain or share when bonding with another atom of a different element. (you will learn more about this in the next chapter…)

How were the Elements Organized and Arranged into the First Periodic Table? Dmitri Mendeleev

The Pattern Medeleev discovered… He arranged all of the cards by increasing atomic mass. After arranging the cards in this order, he noticed a pattern emerging…. All of the valence numbers for each seven elements in a row looked like this… 1 2 3 4 3 2 1

The Pattern Medeleev discovered… The elements kept making this pattern over and over – every 7 elements would increase in valence number, then decrease again. Medeleev noticed that when the cards were arranged in this pattern, the elements created columns. All of the elements in a column had the same valence number and very similar physical and chemical properties!

How the Periodic Table got its name… Meldeleev determined that the elements recurred at regular intervals. He wrote, “the properties of the elements were periodic functions of their atomic masses.” The word periodic means repeating according to a pattern. This is why magazines and newspapers are called “periodicals” – they are printed and published in regular intervals or cycles.

Medeleev’s work allowed him to predict undiscovered elements Medeleev predicted what element #32 would be like…

Medeleev’s work allowed him to predict undiscovered elements

Unfortunately, Medeleev’s work was not 100% accurate…. Remember, Mendeleev used atomic mass to arrange his periodic table… As you know now, the modern Periodic Table is arranged by atomic number!!! In Mendeleev’s table some of the elements appeared to be misplaced because their properties didn’t match the rest of the elements in the column.

Henry Moseley – a young scientist - fixed the problem! 50 years after Mendeleev designed his table, Henry Moseley, a young British scientist determined each Element’s atomic number (# of protons) By using atomic number instead of atomic mass, every element falls into place with similar physical and chemical properties without any exceptions!

Henry Moseley – a young scientist - fixed the problem! Moseley’s discovery of the Periodic Law was the way that the modern Periodic Table was created. Periodic Law – (def) the physical and chemical properties of the elements are periodic functions of their atomic numbers.

Henry Moseley – not your average science geek Henry Moseley completed all of his research by the time he was 27 years old. He was offered a safe job but turned it down to enlist in the British Army to fight in WWI. He was killed by a sniper in Gallipoli, Turkey in August 1915. Many people believe that he would have won the Nobel Prize for his work had he lived. However, it is not awarded to deceased people. It was because of his death that Britain and other world powers decided not to let their scientists enlist in combat anymore.

The Periodic Table – How is it Organized? Vertical Columns are numbered There are 18 main columns of elements. Columns are called groups or families. Elements within a group have similar but not identical properties. Ex – Lithium, Sodium and Potassium are all in column 1 and are all soft, white, shiny metals that are highly reactive (combine easily with other elements to form compounds)

The Periodic Table – How is it Organized? Horizontal rows are called a period. Elements in the same periods are not alike the way that families are alike. The properties of the elements change greatly when moving across a row. The pattern formed by a row is this: Left hand side – extremely reactive solid Right hand side – particularly inactive gas

The Periodic Table Element Key – “What’s in the Box?” The atomic # is THE SAME # AS the # of protons in an atom! The atomic # is only equal to the the number of electrons if the atom is not an ion!!! This is the average atomic mass of all of the isotopes in the UNIVERSE!!!

The Periodic Table – The 3 Major Types of Elements The elements on the periodic table fall into 3 main categories: Metals Nonmetals Metalloids

Metals The majority of the elements are metals. The elements to the left of the dark zigzag line are either metals or metalloids. (except for Hydrogen) Physical Properties: Metallic luster (shiny), good conductors of electricity and heat, high density, high melting points, ductile (can be made into thin wires), malleable (can be made into thin sheets) Chemical Properties Usually give up their valence electrons when bonding, corrosion occurs when the element reacts with water or oxygen.

Nonmetals Fewer of the elements are nonmetals. The elements to the right of the dark zigzag line are nonmetals. Physical and chemical properties are the opposite of metals!!! Physical Properties: No luster (no shine), dull in appearance, poor conductors of heat and electricity, cannot be made into wire or thin sheets (nonductile/nonmalleable), lower density, lower melting point. Chemical Properties Usually gain valence electrons when bonding.

Metalloids Elements that are on either side of the dark zigzag line are metalloids. They have properties of both metals and nonmetals. Metalloid means “metallike”. Solids that can be shiny or dull. Conduct heat and electricity better than nonmetals, but not as well as metals. They are ductile and malleable.

Why the Periodic Table “Makes Sense” based on the Efforts of Mendeleev & Moseley! The work of Mendeleev and Moseley both noted the vertical columns with similar physical and chemical properties. These columns are named Groups or Families. The following are a set of common reactive elements found in Family 1. Note – each of these elements’ atoms contain only 1 electron in their outer shells.

Organization of Periodic Table (Cont’d) The rows of elements are named Periods as shown on Mendeleev’s early Periodic Table. There are a total of seven periods on the Periodic Table.

Organization of Periodic Table (Cont’d) Can you identify the following elements based on your knowledge of periods and rows? Period 3, Family 13 ____ Period 1, Family 2 ____ Period 3, Family 18 ____ Period 4, Family 8 ____

Organization of Periodic Table (Cont’d) Important: Always refer to the Periodic Table KEY to help you in understanding the characteristics of each element. Can you identify any other characteristics or patterns in the Periodic Table based on the Key?

Patterns within the Families (Groups) of the Periodic Table Every element in a family has: The same number of valence electrons Similar physical properties – density, luster, color

Patterns within the Periods of the Periodic Table Every element in a period has: The same number of electron shells As you move across a period from left to right: The elements become less reactive Atomic size decreases Elements become less metallic