Chemistry 11Unit 8 – Atoms and the Period Table

Part III – Periodic Table

1. A short history of the periodic table

Periodic table is an arrangement of chemical

elements organized in terms of their atomic

numbers, electron configurations and properties.

Such a table (or list) did not appear at the

beginning; it is instead a collective work of several

generations of chemists.

The development of the periodic table was in line

with the development of chemical elements (or

inorganic chemistry).

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(1) Antoine Lavoisier (1743-1794)

He was called the father of modern

chemistry.

He published the first ever textbook in

chemistry, “Elementary Treatise of

Chemistry” in 1789.

In his book, he classified hydrogen,

nitrogen, oxygen, phosphorus, sulfur,

zinc and mercury as either metal or

non-metal.

The classification was trivial and

lacked completeness.

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(2) Johann Wolfgang Döbereiner (1780-1849)

He proposed one of the earliest ways

of classifying elements in 1829.

He grouped elements into groups of

three called triads. These elements

possess analogous chemical

properties. For example:

chlorine / bromine / iodine

calcium / strontium / barium

sulfur / selenium / tellurium

lithium / sodium / potassium

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(3) Alexandre-Emile Béguyer de

Chancourtois (1820-1886)

He arranged all known elements

at that time in order of atomic

weights in 1862.

He created a spiral table, telluric

helix, in which species with

similar properties are lined up

vertically.

Not well recognized as it was

given in terms of geology.

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(4) John Newlands (1837-1898)

He was the first to assign atomic numbers to elements in 1864.

He proposed the law of octaves: in many cases elements different by multiple of 8 in mass number show similar properties.

He introduced the concept of periodicity in chemistry.

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His model could not make any prediction, and needed modification whenever new element was discovered.

(5) William Odling (1829-1921)

He published his table in 1864.

He put elements into 7 groups

in order of atomic weights.

He left vacancies for elements

yet to be discovered.

He solved the tellurium-iodine

problem, and was able to

place thallium, lead, mercury

and platinum in correct groups.

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(6) Lothar Meyer (1830-1895)

He was the first to group elements according to their

valence rather than atomic weights.

Two versions of periodic tables were published:

horizontal form (1862, 1864) and vertical form (1870)

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(7) Dmitri Ivanovich Mendeleev (1834-1907)

He arranged all the known elements in

orders of both atomic weights and

valence in 1869.

Elements show periodic patterns of

properties.

He predicted the existence of

undiscovered elements at that moment

such as germanium and gallium.

He suggested that certain properties of

elements can be foretold by their atomic

masses.

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The periodic tables published by Mendeleev:10

(In 1869) (In 1871)

After Mendeleev had proposed his periodic table,

many scientists continued to contribute to its further

modifications. Most notably:

(1) Henry Moseley (1887-1915)

He discovered the physical meaning

of atomic number as the number of

protons in the nucleus of an atom.

He therefore re-sequenced the

periodic table in order of nuclear

charges.

(We have studied his story before)

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(2) William Ramsay (1852-1916), William Strutt (1842-1919)

and Friedrich Ernst Dorn (1848-1916)

They discovered and isolated a

series of gases from minerals

and air which showed

extremely low level of reactivity

during 1894-1898.

Mendeleev added these

elements into group 0 in the

periodic table in 1902.

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(3) Charles Janet (1849-1932)

He proposed an innovative “left-step” periodic table

in 1929.

His table agrees perfectly with quantum theory.

But his table was only up to element 120.

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(4) Glenn T. Seaborg (1912-1999)

He discovered 10 trans-uranium

elements (atomic number: 94-

102, 106) plus many isotopes by

means of nuclear chemistry and

physics.

In order to incorporate these

elements into the periodic table,

he developed the actinide

concept and introduced the

actinide series.

Element 106 (seaborgium) was

named after him in 1997.

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The most up-to-date periodic table (2016 version):15

2. Features of modern periodic table

Chemical elements in the periodic table can be

grouped into several ways.

(1) Groups / Families

A group or family is the set of elements in a given

column going up and down the table.

Elements in one group have the same electron

configurations in their valence shell, hence showing

more significant periodic trends than periods and

blocks.

Groups are numbered from 1 to 18, left to right.

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(2) Periods

A horizontal row of elements in a periodic table

forms a period.

Elements in a period do not usually show trends and

similarities in properties.

For transition and rare earth elements, however,

trends across periods become much more

significant.

For example, lanthanide elements have similar

chemical and physical properties, making them very

difficult to be isolated and purified.

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(3) Blocks

A block of the periodic table refers to a set of

elements in adjacent groups.

Elements within a block have the highest-energy

electrons in the same type of orbitals.

The elements in the periodic table are divided into 4

blocks:

(1) s-block: group 1 and group 2

(2) p-block: groups 13 to 18

(3) d-block: transition metals

(4) f-block: lanthanide and actinide series

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(4) Metals / Metalloids / Non-metals

According to their physical and chemical properties,

elements can be classified into metals, metalloids

and non-metals.

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(i) Metals

Metals share the following

properties:

❖ Lustrous

❖ Opaque

❖ Good electrical and heat

conductors

❖ Malleable and ductile

❖ Solid at room temperature

❖ Reactive to acids

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(ii) Non-metals

Non-metals share the following properties:

❖Mainly gases or solids at room temperature

❖Solid non-metals are brittle

❖Poor heat and electrical conductors

❖Various appearance (dull, opaque, translucent, etc)

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(iii) Metalloids

Metalloids possess properties from both metalsand non-metals (e.g. lustrous but brittle)

Seven metalloids: boron, silicon, germanium, arsenic, antimony, tellurium, polonium

Some of them are semi-conductors, whose electrical conductivity increases with temperature. This is opposite to metals whose conductivity decreaseswith temperature.

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The variation of the metallic behaviors of elements

can be summarized into two trends:

(1) Left to right: decreasing metallic character

(2) top to bottom: increasing metallic character

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The periodic table contains 18 columns categorized

into 4 groups: main group elements, transition elements,

rare earth elements, and synthetic elements.

(1) Main group elements consist of the two columns on

the left and six columns on the right of the table.

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Group # Trivial name IUPAC name (old) IUPAC name (new)

1 Alkali metals IA 1

2 Alkaline earth metals IIA 2

13 Icosagens IIIA 13

14 Crystallogens IVA 14

15 Pnictogens VA 15

16 Chalcogens VIA 16

17 Halogens VIIA 17

18 Noble gases VIIIA 18

Alkali metals

All silvery metals

Low melting points

Very soft

Extremely reactive

in air and water

They are reducing

in nature

In reactions they

form +1 ions.

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Metal M.P. Metals M.P.

Lithium 181°C Rubidium 39°C

Sodium 98°C Cesium 29°C

Potassium 64°C Francium 27°C

Alkaline earth metals

Shiny, silvery-white, and soft

They are reactive in water, forming strongly basic

hydroxides

They form +2 ions in reactions.

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Crystallogens

This group shows a big variation of physical and

chemical properties from carbon to lead.

They are able to exist in +2 or +4 oxidation states.

All members except lead have allotropes (e.g.

graph/diamonds for C, grey/white tin)

Catenation: element can make chains with itself.

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Element Length of catenation

Carbon ∞

Silicon 11-12

Germanium 9-10

Tin 2

Lead 2

Pnictogens

These elements can either gain three electrons or lose

five electrons to form mainly covalent compounds.

They are in general less reactive than group 16

neighbors.

These elements are quite distinctive, and demonstrate

not much connection.

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Chalcogens

These elements are relatively

reactive, forming ions with –2

charges.

They form volatile compounds

with hydrogen.

Their oxides are mainly acidic;

they hydrolyze to form acids.

The chemistry of polonium is

not very well known, because

of its high radioactivity, but

similar to tellurium.

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Halogens

The only group that contains elements in 3 states.

They are extremely reactive, and form a variety of

salts when reacting with metals.

Fluorine is the most reactive element; it even reacts

with glass and noble gases.

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Noble gases

Also called inert gases, as

they virtually do not react

with any elements in the

periodic table.

They are all gases with low

boiling points.

They show different colors

under electric discharge.

Indeed they do react; first

compound was made by Neil

Bartlett at UBC in 1962.

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(2) Transition elements refer to the groups (3 to 12)

sandwiched by the s- and p-block elements.

They are so named because their physical and

chemical properties are somewhat between those

exhibited by s-block and p-block elements.

Their chemistry is very abundant:

(i) versatile oxidation states and charges

(ii) amphoteric when reacting with acids and bases

(iii) forming both ionic and covalent bonds

(iv) very colorful solutions containing transition metal

ions

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(3) Rare earth elements is made of a set of 17 chemical

elements (15 lanthanides plus scandium and yttrium).

The first rare earth, yttrium, was found from a mineral

Ytterbite by Carl Axel Arrhenius in 1787.

They are actually not rare (e.g. cerium has a similar

abundance as copper), but they are geologically

dispersed and not concentrated enough to be

economically or technologically exploitable.

They usually co-exist in nature, and are very difficult

to separate from one another due in part to their

similar chemical properties (related to their f-subshell

electron configurations).

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They all form +3 ions

preferentially in solutions

and compounds.

These elements are widely

used as:

(1) catalytic converters

(2) refining catalysts

(3) superconductors

(4) ultra-strong magnets

(5) lasers

(6) medical fluorophores

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(4) Synthetic elements are the elements that do not

occur naturally on Earth. They are created artificially

using nuclear techniques.

Usually, this term is used for trans-uranium elements

having the atomic numbers of 95 or higher.

The following elements are often obtained by

synthesis although they exist in nature in trace

amounts: Tc, Pm, Po, At, Fr, Ac, Pa, Np, Pu

They are all radioactive and undergo decays to

transform into lighter elements.

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Applications of synthetic elements: cancer therapy, atomic bombs, atomic energy.37

Americium Curium Berkelium Californium

Einsteinium Mendelevium Fermium Lawrencium

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