Elements in Ancient and Medieval Times

Dalton’s elements (1809)

Periodic Table of Elements - History

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 Doebereiner

In 1829, J. Doebereiner classified some elements into groups of three, which he called triads. The elements in a triad had similar chemical properties and orderly physical properties (MODEL OF TRIADS): [Cl2, Br2, I2], [P, As, Sb], [Li, Na, K] and [Ca, Sr, Ba].

John Newlands

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

Telluric Helix of Screw (A. de Chancourtois) (1862)

A. de Chancourtois

Periodic Table of Elements - History

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

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

Dmitri Mendeleev

Lothar Meyer

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?

Original Periodic Table of the Elements

Mendeleev 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).

He used the table to predict the physical properties of three elements that were yet unknown (Sc, Ge, Ga, Tc).

When properties of these elements turned out to be very close to the predicted ones by Mendeleev, his table was widely accepted.

Periodic Table of Elements - History

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?

Periodic Table of Elements - History

Henry Moseley (1913) rearranged the elements in order of increasing atomic number.

Henry Moseley

Ar and K

Co and Ni

Te and I

Th and Pa

Modern Periodic Table of the Elements

Different modern versions of Periodic Table

Round Table of ElementsFractal Table of Elements

Different modern versions of Periodic Table

Energetic blocks in Periodic Table

1s

2s

2p

3s 3p

4s

3d

Physical properties of elements in the Periodic Table

88 metals

17 nonmetals

7 metalloids

Ionization energy

The ionization energy (EI) of an atom or molecule is the minimum

energy required to remove (to infinity) an electron from the atom or molecule isolated in free space and in its ground electronic state.

Electronegativity in Periodic Table

Electronegativity, symbol χ (the Greek letter chi), is a chemical property that describes the ability of an atom to attract electrons towards itself.

Ed(AB) – dissociation energy (eV)

• Van der Waals radius: half the minimum distance between the nuclei of two atoms of the element that are not bound to the same molecule.

• Ionic radius: the radius of the ions deduced from the spacing of atomic nuclei in crystalline salts that include that ion. The length of the ionic bond should equal the sum of their ionic radii.

• Covalent radius: the radius of the atoms of an element when covalently bound to other atoms, as deduced the separation between the atomic nuclei in molecules. The length of a covalent bond should equal the sum of their covalent radii.

• Metallic radius: the radius of atoms of an element when joined to other atoms by metallic bonds.

Atomic radius

Cations are smaller than corresponding atoms.

Anions are larger than corresponding atoms.II/

Due to increased attractionLarger nuclear charge

II/

Factors affecting the atomic radius:

-500

0

500

1000

1500

20002500

3000

3500

4000

4500

H B F Al. Cl

Sc

Mn

Cu

As

Rb

Nb

Rh In I

Tmelt.[ºC]

Melting point

Melting point for a solid is the temperature at which the solid and liquid phases exist in equilibrium.