C3.01 The Periodic Table- classifying the elements

The periodic table was invented by Mendeelev in 1869.

In the periodic table:

The elements are arranged in order of icreasing proton number (atomic number)
The vertical columns of elements with similar properties are called groups
The horizontal rows are called periods
The main distinction in the table is between metal and non- metal

METAL AND NON-METAL

METAL: an element that conducts electricity and is malleable and ductile.

NON-METAL: an element that does not conduct electricity well and is neither malleable nor ductile.

METALLOIDS

The elements close to the line which divide metals from non-metals show properties that lie between these extremes. Often, we refer to these elements as METALLOIDS or SEMI-METALS. In particular, there are eight of these metalloids.

SOME PROPERTIES:

They might look like metals, but are brittle like non-metals.
They are neither conductors nor insulators, but make excellent semiconductors.

Boron

Silicon

Germanium

Arsenic

Antimony

Tellurium

Polonium

Astatine

GROUPS AND PERIODS IN THE PERIODIC TABLE

Main-group elements: Group from I to VIII
The elements in the same group have similar chemical and physical properties. Some of them have also a specific name and number
Transition elements: Group I and II, the first row of these elements occur in Period 4 (Iron, zinc, copper...)
Nobel gases, in Group VIII, are the least reactive elements
Halogens (Group VII) and Alkali metals (Group I) are the most reactive elements

ELECTRON ARRANGEMENT AND THE PERIODIC TABLE

Nowadays we know exactly the properties of an element with its position in the Table and the electron arrangement.
Elements in the same group have the same number of outer electrons, By the way, as we move across a period in the table a shell of electrons is being filled.
There is a clear relationship between electrons arrangement and position in the Period Table: the elements in Group II have two outer electrons, in Group III they have three outer electrons... and so on. So, for the main-group elements, the number of the group is the number of electrons in the outer shell.

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