Periodic Trends!

Periodic Law

When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.

There are many trends in the periodic table, but you must know the reasoning behind 3 of them

Atomic Radius:

Gives us an idea of the size of an atom

The trend:A.R. increases as you move down a

groupA.R. decreases as you move across a

period from left to right

Why?

As atomic # increases, the number of protons and electrons increases

To accommodate the electrons, there must be more energy levels. This is why A.R. increases as you move down a group.

As you go across a period, an atom is not gaining energy levels The atom is still gaining protons and electrons, though, so the

atom becomes more and more dense This causes the electrons to be drawn closer to the positive

nucleus. This is why A.R. decreases as you move across a

period.

Ionization Energy

The energy required to remove an electron from the valence shell of an atom

The trend:

I.E. decreases as you go down a group

I.E. increases as you go across a period from left to right

Draw the arrows for the trend on the periodic table sheet!

Why?

As you go down a group, the atomic radius increases

This means that the valence electrons in a large atom are further away from the nucleus, than the valence electrons in a small atom

If the valence electrons are far away from the positive nucleus, it will take less energy to remove them. Large atoms tend to be lower down in a group. This is why I.E. decreases as you go down a group.

As you go across a period, atomic radius decreases

This means the electrons will be held closer and closer to the positive nucleus as you go across the period

This means that atoms of elements to the right of the periodic table will have valence electrons that are harder to remove. This is why I.E. increases as you go across a period.

Electronegativitythe tendency of an atom to attract

electrons to itself when it is chemically combined with other elements

The trend:

E.N. decreases as you go down a group

E.N. increases as you go across a period left to right

Draw the arrows for the trend on the periodic table sheet!

Why?

As you go down a group, the atomic radius increases

This means that in elements lower down in the group, the additional electrons will not feel a strong attraction to the nucleus, which is already surrounded by electrons. This is why E.N. decreases as you go down a group.

As you go across a period, the atomic radius decreases

This means that in elements further to the right, additional electrons will feel a stronger attraction to the nucleus than in elements further to the left. This is why E.N. increases as you go across a period.