The Periodic Table

Unit 3

Chapter 4

pp 114-131

Ok, so now what?

Recall: Element cannot be broken down any further.

In the late 1800’s, we had “discovered” about 60 elements.

We had no idea of the structure of atoms. Many scientists attempted to put order to the

rapidly expanding list of elements.

Off to the Newlands…

Arranged known elements in a table by atomic mass in 1863.

Noticed a repeating pattern every 8th element in 1865.

Law of Octaves – chemical properties repeat every 8 elements.

Was laughed at by peers.John Newlands

(1837-1898)

Newland’s Flaw

Knew nothing of subatomic particles His table mixed some obviously different elements

(like oxygen and iron)

The Mad Russian

Produced a more orderly table independent of Newlands’ work in 1869 (also used atomic mass).

Left blanks for yet-undiscovered elements.

Predicted properties of Ga, Sc, and Ge (disc. 1875, 1877, & 1886).

Credited with the Periodic Table.

Dmitri Mendeleev(1834-1907)

Russian Roulette

Mendeleev’s table had a few problems.

Based on atomic mass, had to switch a few elements (e.g. Tellurium and Iodine) to keep reactivities in order.

Many believed he predicted too many elements (we had 63 already!!!).

Still, this is what we used for half a century.

45 Years Later…

Rearranged table according to electronic charge in 1914. Became the # of protons after 1918.

Noticed his new table had spots for #’s 43, 61, 72, & 75.

Produced the modern periodic table we know today.

Enlisted in the army’s Royal Engineers when WWI broke out.

Henry Moseley(1887 – 1915)

Moseley’s New Order

Gave experimental meaning to atomic number.

Gave reason for Tellurium and Iodine being switched.

Moseley’s technique easily separated rare earth metals. Plagued chemists for years and years.

Predicted how many elements remained between others.

(e.g. 13 elements between La and Lu)

Moseley’s Lost Nobel

Many thought he should have won Nobel Prize. It’s only given to the living…he was shot in the head

by a sniper in Gallipoli. Bohr (1962): "You see actually the Rutherford work

[the nuclear atom] was not taken seriously. We cannot understand today, but it was not taken seriously at all. There was no mention of it any place. The great change came from Moseley."

British barred scientists from enlisting for combat.

294118Uuo

Elements Everywhere

Based on increasing number of protons, we now have a complete periodic table.

Will not find any lower elements, can only go up (118 so far).

Create new elements by smashing smaller atoms together:

4820

Ca 249 98Cf

3 Neutrons

Periodicity

In order by atomic number (# of Protons) H has 1 p+, U has 92

Arranged in Rows and Columns Rows = Periods

Pd 3 = Na, Mg, Al, Si, P, S, Cl, Ar Columns = Groups or Families

Group 1 = H, Li, Na, K, Rb, Cs, Fr Have similar properties (e.g. Form hydroxides: LiOH, NaOH, KOH, etc)

Division of Labor

Different types of elements are found on different parts of the table: Metals to the left (majority of the elements). Nonmetals to the right (18 elements). Metalloids found on a “staircase” dividing metals

and nonmetals (7 elements). Lanthanoids & Actinoids (metals) added to bottom

to make table manageable.

Metals

Lustrous (shiny) Malleable (can be pounded into

thin sheets) Ductile (can be pulled into

wires) Conductive

Heat and electricity

Form solid oxides when burned. Tend to react with acids to form

Hydrogen gas.

Nonmetals

Wide range of properties Tend to:

Be Dull Be Brittle (when solid) Be Insulators Form gaseous oxides Not react with acids Have lower melting & boiling

points.

Bromine

Metalloids

Also called “semi-metals” or “staircase elements.”

Combination of properties of metals and nonmetals.

Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, & Polonium

Many exhibit semi-conducting behavior.

Groups/Families

Alkali Metals Alkali Earth Metals Halogens Noble Gases Transition Metals Inner Transition Metals

Lanthanoids (Rare Earths) Actinoids

s-Block Elements

At least 1 e- in s orbital (nsx) Groups 1 & 2

Alkali Metals Alkaline Earth Metals

Reactivity increases as you go down All are metals, except H & He Helium is technically an s-block, but placed

with Noble Gases b/c of reactivity

p-Block Elements

At least 1 e- in p orbital (npx) Groups 13-18 Nonmetals at top, gradually transitioning into

metals All nonmetals and metalloids are p-block

elements (excl H & He) Some metals (Al, Ga, In, Sn, Tl, Pb, Bi)

d-Block Elements

At least 1 e- in d orbital (ndx) Groups 3-12

Transition Metals Very little similarities w/in group All are metals Most form multiple ions (charged atoms)

f-Block Elements

At least 1 e- in f orbital (nfx) Oddballs

Lanthanoids start with #57, La Actinoids start with #89, Ac

The groups are NOT similar up & down All are metals Lanthanoids (4f) are natural, most Actinoids

(5f) are man-made

Representative Elements

Exhibit nearly perfect periodicity. All members of these groups behave as

expected. Groups on the outside of the table:

Alkali Metals (Group 1) Alkaline Earth Metals (Group 2) Halogens (Group 17) Noble Gases (Group 18)

Alkali Metals

Group 1 (excluding hydrogen) [ns1] Soft, lustrous, oxidize when exposed to air. Difficult to isolate – never found in nature. React (violently) with water to form a base. React with chlorine to form a salt with a 1-to-1 ratio:

LiCl NaCl KCl RbCl CsCl (also FrCl)

Alkaline Earth Metals

Group 2 [ns2] Harder & Denser than Alkali Metals. Lustrous, oxidize slowly when exposed to air. React with water or steam to form a base. React with chlorine to form a salt with a 1-to-2 ratio:

BeCl2 MgCl2 CaCl2 SrCl2 BaCl2 RaCl2

Halogens

Group 17 [np5] Nonmetals Gases (F, Cl), liquid (Br), and solids (I, At) Name means “salt former.” React with sodium to form a salt with a 1-to-1 ratio:

NaF NaCl NaBr NaI NaAt

Noble Gases

Group 18 [np6] Unreactive Gases – colorless, odorless. Some of the last natural elements to be discovered. Once called “Inert Gases.” Monatomic in Nature

Non-representatives

Other families have similarities, but do not behave exactly as expected Groups 13-16, start with Boron – Oxygen More differences than similarities

Others are lumped together for other reasons Transition Metals Lanthanoids Actinoids

Transition Metals

Groups 3 to 12 [ndx] Central portion of the PT. Behavior and appearance vary. Variable oxidation state (charge). Different oxidation states can produce different

colors. Often used to make pigments.

Co+2 Cr+6 Cr+6 Ni+2 Cu+2 Mn+7

Lanthanoids

1st Row on Bottom of table [4fx] AKA Lanthanides & Rare Earths Not so rare (Ce 25th most abundant) So similar, very difficult to separate –

remember Moseley? Most deflect UV – used in sunglasses Shiny, silvery white, soft, react violently with

most nonmetals, tarnish in air

Actinoids

2nd Row on Bottom of table [5fx] AKA Actinides All are radioactive Not as similar as the Lanthanoids Only Th and U are common in nature Most are man-made

Nuclear fallout Particle colliders

State of the Union

Reacted State: When elements are combined with other

elements to form compounds Most common state

Elemental State: When elements are uncombined Most elements are Monatomic (one atom) Some are always Diatomic (two atoms) A few are Polyatomic (>2 atoms)

Diatomics

7 elements always form diatomic molecules when they are isolated in their elemental state…ALWAYS!

Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, & Iodine

These, you gotta memorize! Luckily, Mr. Brinclhof is here to help!

Br2 I2 N2 Cl2 H2 O2 F2

Another Way

The rule of “7” Diatomics form a “7” on

the Periodic Table excluding H

C N O F

Si P S Cl

Ge As Se Br

Sn Sb Te I

H

2 2 2

2

2

2

2

The Oddballs

Sulfur is normally found as S8

Selenium also forms Se8

Phosphorus forms P4

Allotrope

When an element can be found in more than one form

Several elements have different allotropes, but most often cited is Carbon

Carbon has 3 common allotropes Amorphous – Random arrangement of C atoms Graphite – Hexagonal arrangement in sheets

Conducts electricity! Diamond – 3-D network solid

Allotropes of C

Amorphous C

Diamond(Network Solid)

Graphite(Sheets)

Trends in the Periodic Table

Several trends appear once we have the elements in order Atomic Radius Ionization Energy Electronegativity Reactivity

Ray “D” Eye

Atomic Radii DECREASE from left to right

They INCREASE from top to bottom

Na is bigger than Ar

(223 pm) (88 pm)

I is bigger than F(132 pm) (57 pm)

Na Mg Al Si P S Cl Ar

I

Br

Cl

F

Fluorine says, “Mine!”

Electronegativity is a measure of how badly an element wants to gain an electron

It INCREASES from left to right It DECREASES from top to bottom

Li

0.98

Be

1.57

B

2.04

C

2.55

N

3.04

O

3.44

F

3.98

Ne

--

Cl

3.16

Br

2.96

I

2.66

F has Codependency Issues

Ionization Energy is the amount of energy required to remove an electron. It INCREASES from left to right

It DECREASES from top to bottom

Na needs less NRG than Cl(496 kj/mol) (1256 kj/mol)

F needs more NRG than I(1681 kj/mol) (1008 kj/mol)

Major Trends in a Nutshell

Atomic Radius Decreases

Electronegativity Increases

Ionization Energy Increases

Fr

F

We usually ignore the Noble Gases

Reactivity

Most reactive Metals are farther down and to the left

Most reactive Nonmetals are higher and to the right

Tidbits

Hydrogen by far most abundant (4 out of every 5 atoms in universe)

Atoms in the Elemental state tend to be more dangerous/poisonous than those in the Reacted state – Exceptions: Cu & Pb

Oddo-Harkins Rule: even #’d elements more common than odd ones (protons apparently like to be paired up).