Chapter 6

Cl ifi ti f Classification of Elements: Elements:

The Periodic TableThe Periodic Table

How were the Elements Organized

gand Arranged into the First

Periodic Table? Dmitri Mendeleev – Russian chemist from the Mid

1800’sH k ll f h i f h ll d b h 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 The properties that he wrote down were both physical (atomic mass, color, density, melting point) and chemical (reactivity and atomic bonding)Th b di d t i ll d l b thi 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 gdifferent element. (you will learn more about this in the next chapter…)

How were the Elements Organized d d h F P d

gand Arranged into the First Periodic

Table?

Dmitri M d lMendeleev

Th P M d l di dThe Pattern Medeleev discovered…

He arranged all of the cards by increasing atomic mass.atomic mass.

After arranging the cards in this order, he noticed a pattern emerging….

All of the valences – the numbers of outer shell electrons - for each seven elements in a row looked like thisrow looked like this…

1 2 3 4 3 2 11 2 3 4 3 2 1

Th P M d l di dThe Pattern Medeleev discovered…

The elements kept making this pattern over and over – every 7 elements would increase in and over every 7 elements would increase in valence number, then decrease again.

Medeleev noticed that when the cards were 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 How the Periodic Table got its name…

Meldeleev determined that the elements recurred at regular intervalsrecurred at regular intervals.

He wrote, “the properties of the elements were periodic functions of their atomic were periodic functions of their atomic masses.”

The word periodic means repeating 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 Medeleev s work allowed him to predict undiscovered elements

Medeleev predicted whatpredicted what element #32 would be liklike…

Medeleev’s work allowed him to Medeleev s work allowed him to predict undiscovered elements

Unfortunately Medeleev’s work Unfortunately, Medeleev s work was not 100% accurate….

Remember, Mendeleev used atomic mass to arrange his periodic tablearrange his periodic table… As you know now, the modern Periodic

Table is arranged by atomic number!!!Table is arranged by atomic number!!! In Mendeleev’s table some of the elements

appeared to be misplaced because theirappeared to be misplaced because their properties didn’t match the rest of the elements in the column.e e e s e co u .

Henry Moseley – a young Henry Moseley a young scientist - fixed the problem!

50 years after Mendeleev designed his table, Henry g , yMoseley, a young British scientist determined each Element’s atomic number Element s atomic number (# of protons)

By using atomic number i t d f t i instead of atomic mass, every element falls into place with similar physical p p yand chemical properties without any exceptions!

Henry Moseley – a young Henry Moseley – a young scientist - fixed the problem!

Moseley’s discovery of the Periodic Lawwas the way that the modern Periodic was the way that the modern Periodic Table was created. P ri dic L (d f) th ph sic l nd Periodic Law – (def) the physical and chemical properties of the elements are periodic functions of their atomic are periodic functions of their atomic numbers.

Henry Moseley – not your 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 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 He was killed by a sniper in Gallipoli, Turkey in August 1915.

Many people believe that he would have won the y p pNobel Prize for his work had he lived. However, it is not awarded to deceased people.

It was because of his death that Britain and 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 –The Periodic Table –How is it Organized?

Vertical Columns are numbered There are 18 main columns of elements There are 18 main columns of elements. Columns are called groups or families.

El t ithi h i il b t t Elements within a group have similar but not identical properties.

Ex Lithium Sodium and Potassium are all in Ex – Lithium, Sodium and Potassium are all in column 1 and are all soft, white, shiny metals that are highly reactive (combine easily with that are highly reactive (combine easily with other elements to form compounds)

The Periodic Table –The Periodic Table –How is it Organized?

Horizontal rows are called a period. Elements in the same periods are not alike the Elements in the same periods are not alike the

way that families are alike. The properties of the elements change greatlyThe 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 –The Periodic Table Element Key –“What’s in the Box?”

The atomic # is THE SAME # AS the # of protons

The atomic # is l l h

the # of protonsin an atom!

only equal to the the number of electrons if the atom is not an ion!!!This is the average atomic mass of all atomic mass of all of the isotopes in the UNIVERSE!!!

The Periodic Table –The Periodic Table The 3 Major Types of Elements

The elements on the periodic table fall into 3 main categories:into 3 main categories: Metals

N l Nonmetals Metalloids

M lMetals

The majority of the elements are metals. The elements to the left of the dark zigzag line

are either metals or metalloids (except for are either metals or metalloids. (except for Hydrogen)

Physical Properties:y p 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 i t thi h t )into thin sheets)

Chemical Properties Usually give up their valence electrons when bonding, sua y g up th r a nc ctrons wh n on ng,

corrosion occurs when the element reacts with wateror oxygen.

N lNonmetals

Fewer of the elements are nonmetals. The elements to the right of the dark zigzag

l l g g g

line are nonmetals. Physical and chemical properties are the

opposite of metals!!!opposite of metals!!! Physical Properties:

No luster (no shine), dull in appearance, poor d f h d l b d

pp pconductors 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.

M ll idMetalloids

Elements that are on either side of the dark zigzag line are metalloids.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 They are ductile and malleable.

Why the Periodic Table “Makes Sense” based on the

Eff f Efforts of Mendeleev & Moseley!

The work of Mendeleev and Moseley both noted the vertical columns with i il h i l d h i l similar physical and chemical

properties. These columns are named Groups or These columns are named Groups or

Families. The following are a set of common The following are a set of common

reactive elements found in Family 1. Note – each of these elements’ Note each of these elements

atoms contain only 1 electron in their outer shells.

Organization of Periodic Table Organization of Periodic Table (Cont’d)

The rows of elements are named elements are named Periods as shown on Mendeleev’s early Mendeleev s early Periodic Table. Th t t l There are a total

of seven periods on th P i di T blthe Periodic Table.

Organization of Periodic Table Organization of Periodic Table (Cont’d)

Can you identify the following elements based on your knowledge of periods and rows?y g p

Period 3, Family 13 ____

Period 1, Family 2 ____

Period 3 Family 18 Period 3, Family 18 ____

Period 4, Family 8 ____, y ____

Organization of Periodic Table Organization of Periodic Table (Cont’d)

Important: Always refer to the Periodic T bl KEY t h l Table KEY to help you in understanding the characteristics of each characteristics of each element.

Can you identify any Can you identify any other characteristics or patterns in the P i di T bl b d Periodic Table based on the Key?

Patterns within the Families Patterns within the Families (Groups) of the Periodic Table

Every element in a family has:Th s m n mb f l n l t ns The same number of valence electrons

Similar physical properties – density, luster, color color

Patterns within the Periods of the

E

Patterns within the Periods of the Periodic Table

Every element in a period has:period has: The same

number of number of electron shells

•As you move across a period from left to •As you move across a period from left to right:

The elements become less reactiveThe elements become less reactive Atomic size decreases Elements become less metallic