The Periodic Table

Unit 5

Chapter 5

Ok, so now what?

Recall that elements 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 (which were discovered in 1875, 1877, & 1886).

Credited with developing the Periodic Table.

Dmitri Mendeleev(1834-1907)

Russian Roulette

Mendeleev’s table had a few problems.

Based on atomic weight, he had to switch a few elements (e.g. Tellurium and Iodine) to keep the 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 Periodic Table

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.

Used to predict 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."

Moseley’s promising career was cut short. Because of this, the British barred scientists from

enlisting for combat.

The Modern Periodic Table

A chart of the elements showing the repeating pattern of their properties.

Elements are arranged in rows and columns by increasing atomic number.

The atomic number increases by 1 between each element.

Rows & Columns

A vertical column is called a group or family because…

Elements in columns have similar properties.

A horizontal row of elements is called a Period because…

Properties repeat periodically

Xe

Ar

B C N O F

Kr

Ne

He

Period 2(Not similar at all)

Group 18The Noble Gases

Li Be

Rn

Info on the Table

Periodic Tables include the chemical symbols of the elements.

These are 1 or 2 letter abbreviations for the elements.

The table is arranged by atomic number

This is the number of protons in the nucleus.

HeHeHeliumHelium

22

More Stuff

The tables also include the atomic weight. This is the average mass of an atom of the

element.

HeHeHeliumHelium

22

4.0026024.002602

The Atomic Weightvaries dependingupon where youfind your sample!

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).

We can create new elements by smashing smaller atoms together:

4820

Ca 249 98Cf

3 Neutrons

Division of Labor

Different types of elements are found on different parts of the Periodic Table:

Metals to the left (majority of the elements). Nonmetals to the right (10 elements). Noble Gases (Group 18) Metalloids found on a “staircase” dividing

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

bottom to make table manageable.

Metals are

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 have a

Wide range of properties They tend to: Be Dull Brittle (when solid) & Insulators They form gaseous oxides Do not react much 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.

Semiconductors

Conduct electricity better than insulators, but worse than conductors.

Conductivity usually increases with an increase in temperature.

Semiconductors are used extensively in computers, most notably Silicon.

Properties can be modified by adding impurities – this is called “doping.”

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 (or lack of)

p-Block Elements

At least 1 e- in p orbital (npx) Groups 13-18 The nonmetals are at the top and they

gradually transition into metals All nonmetals and metalloids are p-block

elements (excl H & He) Only a few p-Block metals (Al, Ga, In, Sn, Tl,

Pb, Bi)

d-Block Elements

At least 1 e- in d orbital (ndx) Groups 3-12 Called the Transition Metals Very little similarities within the group All are metals & Most form ions with multiple charges.

f-Block Elements

At least 1 e- in f orbital (nfx) These are the oddballs

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

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

Actinoids (5f) are man-made

Why are they there?!?

The f-block elements are placed at the bottom of the periodic table to make the table manageable.

They should fit in between the s-block and d-block elements, but

That would make the table too long:

s p

fd

H He