The table consists of periods and families.

The mere location of a chemical element in the periodic table may already indicate several specific characteristics of that element.

The periods

Elements are distributed in the table in ascending order from left to right in horizontal rows according to number atomic (Z) of each element, which is above its symbol.

Look at the table above. In the table there are seven horizontal lines, which are called periods.

Periods indicate the number of electronic layers or levels the atom has. For example, potassium (K) is located in the fourth period, and cesium (Cs) in the sixth period. This means that in electronic distribution potassium has four layers or electronic levels and cesium has six.

Palladium (Pd) is an exception: although it is in the fifth horizontal line, it has only four electronic layers or levels.

Elements of the same period have the same number of electronic layers, which in turn coincides with the period number. For example:

PeriodNo. of layersLayers
1 1 K
2 2 K L
3 3 K L M
4 4 K L M N
5 5 K L M N O
6 6 K L M N O P
7 7 K L M N O P Q

The families

Note that in the periodic table there are 18 vertical rows or columns. They represent families or groups of chemical elements.

Above the columns are numbers (1, 2, 3 etc.).

Each column represents a family; for example:

  • 1 is the family of alkali metals;
  • 2 is the family donates earth alkaline;
  • 18 is the family of noble gases.

Each chemical family groups its elements according to similarity in properties. For example, family 11 is composed of the chemical elements copper (Cu), silver (Ag) and gold (Au). They are part of the group of metals and have common characteristics: metallic luster, malleability, ductility, are good conductors of heat and electricity.

So with these other elements, the same family have similarities in their properties.

The number of some families indicates how many electrons the chemical element has in the last layer of its electrosphere. Here are some examples.

  • Sodium (Na) is in family 1, ie it has an electron in the last layer of its electrosphere.
  • Magnesium (MG) is in family 2, ie it has an electron in the last layer of its electrosphere.
  • Aluminum (Al) is in family 3, because this element has three electrons in the last layer of its electrosphere.

The chemical elements in families 1 and 2 have the number of electrons in the last shell equal to the number of the family to which they belong.

For families 13 through 18, the number of electrons in the last layer is obtained by subtracting 10 from the family number. In other families this rule cannot be applied.

Helium, despite being in family 18, has only two electrons in the last shell, because this element has only two electrons.

Family # Of electrons in last layer
1 1
2 2
13 3
14 4
15 5
16 6
17 7
18 8