The Periodic Table

Chapter 12

Why is the Periodic Table important to me?

• The periodic table is the most useful tool to a chemist.

• It organizes lots of information about all the known elements.

Pre-Periodic Table Chemistry …

• …was a mess!!!• No organization of

elements.• Imagine going to a grocery

store with no organization!!• Difficult to find information.• Chemistry didn’t make

sense.

Elements

• Science has come along way since Aristotle’s theory of Air, Water, Fire, and Earth.

• Scientists have identified 90 naturally occurring elements, and created about 28 others.

The History of the Modern Periodic Table

During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table.

Johann Dobereiner

1780 - 1849

Model of triads

In 1829, he classified some elements into groups of three, which he called triads.The elements in a triad had similar chemical properties and orderly physical properties.

(ex. Cl, Br, I andCa, Sr, Ba)

John Newlands

1838 - 1898

Law of Octaves

In 1863, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element.

John Newlands

1838 - 1898 Law of Octaves

Newlands' claim to see a repeating pattern was met with savage ridicule on its announcement. His classification of the elements, he was told, was as arbitrary as putting them in alphabetical order and his paper was rejected for publication by the Chemical Society.

John Newlands

1838 - 1898 Law of Octaves

His law of octaves failed beyond the element calcium. WHY?

Would his law of octaves work today with the first 20 elements?

Dmitri Mendeleev

1834 - 1907

In 1869 he published a table of the elements organized by increasing atomic mass.

Lothar Meyer

1830 - 1895

At the same time, he published his own table of the elements organized by increasing atomic mass.

• Both Mendeleev and Meyer arranged the elements in order of increasing atomic mass.

• Both left vacant spaces where unknown elements should fit.

So why is Mendeleev called the “father of the modern periodic table” and not Meyer, or both?

• stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong. (He corrected the atomic masses of Be, In, and U)

• was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown.

Mendeleev...

After the discovery of these unknown elements between 1874 and 1885, and the fact that Mendeleev’s predictions for Sc, Ga, and Ge were amazingly close to the actual values, his table was generally accepted.

However, in spite of Mendeleev’s great achievement, problems arose when new elements were discovered and more accurate atomic weights determined. By looking at our modern periodic table, can you identify what problems might have caused chemists a headache?

Ar and KCo and NiTe and I

Th and Pa

Henry Moseley

1887 - 1915

In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number.*“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.”

Henry Moseley

His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting in Gallipoli by a sniper’s bullet, at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.

Glenn T. SeaborgAfter co-discovering 10 new elements, in 1944 he moved 14 elements out of the main body of the periodic table to their current location below the Lanthanide series. These became knownas the Actinide series.

1912 - 1999

Glenn T. SeaborgHe is the only person to have an element named after him while still alive.

1912 - 1999

"This is the greatest honor ever bestowed upon me - even better, I think, thanwinning the Nobel Prize."

Periodic Table• The periodic table organizes the elements in a particular way. A

great deal of information about an element can be gathered from its position in the period table.

• For example, you can predict with reasonably good accuracy the physical and chemical properties of the element. You can also predict what other elements a particular element will react with chemically.

• Understanding the organization and plan of the periodic table will help you obtain basic information about each of the 118 known elements.

The Current Periodic Table

• Mendeleev wasn’t too far off.• Now the elements are put in rows by increasing

ATOMIC NUMBER!!• The horizontal rows are called periods and are

labeled from 1 to 7.• The vertical columns are called groups are

labeled from 1 to 18.

Groups…Here’s Where the Periodic Table Gets Useful!!

• Elements in the same group have similar chemical and physical properties!!

• (Mendeleev did that on purpose.)

Why??• They have the same

number of valence electrons.

• They will form the same kinds of ions.

Periodic LawWhen elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.

Properties of Non-Metals

• Non-metals are poor conductors of heat and electricity.

• Non-metals are not ductile or malleable.

• Solid non-metals are brittle and break easily.

• They are dull.• Many non-metals are gases.

Sulfur

Properties of Metalloids/Semiconductors

• Metalloids (metal-like) have properties of both metals and non-metals.

• They are solids that can be shiny or dull.

• They conduct heat and electricity better than non-metals but not as well as metals.

• They are ductile and malleable.

Silicon

Families Periods• Columns of elements are called

groups or families. • Elements in each family have

similar but not identical properties.• For example, lithium (Li), sodium

(Na), potassium (K), and other members of family IA are all soft, white, shiny metals.

• All elements in a family have the same number of valence electrons.

• Each horizontal row of elements is called a period.

• The elements in a period are not alike in properties.

• In fact, the properties change greatly across even given row.

• The first element in a period is always an extremely active solid. The last element in a period, is always an inactive gas.

Families on the Periodic Table

• Columns are also grouped into families.

• Families may be one column, or several columns put together.

• Families have names rather than numbers. (Just like your family has a common last name.)

Hydrogen

• Hydrogen belongs to a family of its own.

• Hydrogen is a diatomic, reactive gas.

• Hydrogen was involved in the explosion of the Hindenberg.

• Hydrogen is promising as an alternative fuel source for automobiles

Hydrogen

• It’s a gas at room temperature.• It has one proton and one electron in its one and

only energy level.• Hydrogen only needs 2 electrons to fill up its

valence shell.

Alkali Metals

• 1st column on the periodic table (Group 1) not including hydrogen.

• Very reactive metals, always combined with something else in nature (like in salt).

• Soft enough to cut with a butter knife

Alkali Metals

• Atoms of the alkali metals have a single electron in their outermost level, in other words, 1 valence electron.

• They are shiny, have the consistency of clay, and are easily cut with a knife.

Alkali Metals

• They are the most reactive metals.

• They react violently with water.

• Alkali metals are never found as free elements in nature. They are always bonded with another element.

Alkaline Earth Metals

• Second column on the periodic table. (Group 2)

• Reactive metals that are always combined with nonmetals in nature.

• Several of these elements are important mineral nutrients (such as Mg and Ca

Alkaline Earth Metals

• They are never found uncombined in nature.• They have two valence electrons.• Alkaline earth metals include magnesium and calcium,

among others.

Transition Metals

• Elements in groups 3-12• Less reactive harder

metals• Includes metals used in

jewelry and construction.• Metals used “as metal.”

Transition Metals

• Transition Elements include those elements in the B families.

• These are the metals you are probably most familiar: copper, tin, zinc, iron, nickel, gold, and silver.

• They are good conductors of heat and electricity.

Transition Elements

• Transition elements have properties similar to one another and to other metals, but their properties do not fit in with those of any other family.

• Many transition metals combine chemically with oxygen to form compounds called oxides.

Boron Family

• Elements in group 13• Aluminum metal was

once rare and expensive, not a “disposable metal.”

Boron Family

• The Boron Family is named after the first element in the family.

• Atoms in this family have 3 valence electrons.

• This family includes a metalloid (boron), and the rest are metals.

• This family includes the most abundant metal in the earth’s crust (aluminum).

Carbon Family • Elements in group 14• Contains elements

important to life and computers.

• Carbon is the basis for an entire branch of chemistry.

• Silicon and Germanium are important semiconductors.

Carbon Family

• Atoms of this family have 4 valence electrons.

• This family includes a non-metal (carbon), metalloids, and metals.

• The element carbon is called the “basis of life.” There is an entire branch of chemistry devoted to carbon compounds called organic chemistry.

Nitrogen Family• Elements in group 15• Nitrogen and phosphorus

are both important in living things.

• Most of the world’s nitrogen is not available to living things.

• The red stuff on the tip of matches is phosphorus.

Oxygen Family or Chalcogens

• Elements in group 16• Oxygen is necessary for

respiration.• Many things that stink,

contain sulfur (rotten eggs, garlic, skunks,etc.)

Oxygen Family

• Atoms of this family have 6 valence electrons.

• Most elements in this family share electrons when forming compounds.

• Oxygen is the most abundant element in the earth’s crust. It is extremely active and combines with almost all elements.

Halogens

• Elements in group 17• Very reactive, volatile,

diatomic, nonmetals• Always found combined

with other element in nature .

• Used as disinfectants and to strengthen teeth.

Halogen Family

• The elements in this family are fluorine, chlorine, bromine, iodine, and astatine.

• Halogens have 7 valence electrons, which explains why they are the most active non-metals. They are never found free in nature. Halogen atoms only need

to gain 1 electron to fill their outermost energy level.They react with alkali metals to form salts.

The Noble Gases

The Noble Gases

• Elements in group 18• VERY unreactive,

monatomic gases• Used in lighted “neon”

signs• Used in blimps to fix the

Hindenberg problem.• Have a full valence shell.

Noble Gases

• Noble Gases are colorless gases that are extremely un-reactive. • One important property of the noble gases is their inactivity. They are inactive

because their outermost energy level is full. • Because they do not readily combine with other elements to form compounds, the

noble gases are called inert.• The family of noble gases includes helium, neon, argon, krypton, xenon, and radon. • All the noble gases are found in small amounts in the earth's atmosphere.

Rare Earth Elements

• The thirty rare earth elements are composed of the lanthanide and actinide series.

• One element of the lanthanide series and most of the elements in the actinide series are called trans-uranium, which means synthetic or man-made.

The Octet RuleOctet Rule: Atoms tend to gain, lose or share

electrons so as to have 8 electrons in their outer electron shell, a stable arrangement.

To determine if an atom has a stable arrangement, we will modify our electron arrangement drawings to include only the outer electrons. This is called the Lewis Dot Structure and some examples follow:

           

                                                

             

We begin by imagining a box around the symbol, and add one electron to each side (exception: He). If there are more than 4 electrons, the next time around the box, they pair up, see N for example.

First, we use the atomic number. For N, that is _______. Therefore the number of valence electrons is ______. We should also note which family N is in. In that family all members have ________ outer electrons.

Stability and the Octet Rule

N•

•

•

••

5 6 7 full

More Lewis Dot Examples

P 5 6 7 full•

••

••

Cl•

••

••

••

What does P need for a stable, noble-gas-like arrangement?

What does Cl need?

Stability and the Octet Rule• Recall the patterns in the periodic chart, how do you

know how many valence electrons an element has?

• As it turns out, atoms bond together for a very simple reason: to gain stability.

• Are there more stable or unstable elements then?

** Because they already have a full valence energy level. **

The noble gases are stable meaning they seldom form bonds with other atoms. Why not?

Stop and Think

Distinguish between these two terms as applied to atoms:

• Stable• Neutral

How does an atom of Cl get stable?

Once it’s stable it is no longer neutral. Let’s see why.

Becoming stable• Cl, atomic number 17. That means it has 17 positive

charges–protons–in the nucleus and by inference, 17 negative charges, electrons.

• But, if it takes on an additional electron to achieve a stable arrangement, the balance of positive and negative charges changes.

• There would now be the same 17 protons, but 18 electrons, giving the atom a -1 charge.

• It is thus stable but NOT neutral.

•-1

An atom with a charge is called an ion.