Trends in the Periodic Table 1.7

Mendeleev’s original periodic table arranged elements in order of increasing _____

Atomic mass

The modern periodic table arranges elements in order of increasing ___

Atomic number

According to the periodic law

The chemical and physical properties of the elements repeat in a regular, periodic pattern when they are arranged according to atomic number

Trends in the periodic table

The periodic trends that result from organizing elements by their atomic number, are linked to the way electrons occupy and fill energy levels

1. Atomic radius

2. Ionization energy

3. Electron affinity

Atomic radius

• the distance from the center of an atom (nucleus) to the outermost (valence) electrons.

• usually expressed in pm (picometres, or one trillionth of a metre).

• Increases on the periodic table (right to left and top to bottom)

Atomic radius across a row

• The valence electrons are in the same energy level, so the number of protons in the nucleus matters.

• As you go right to left across a row, the number of protons decreases.

• As a result, the attraction between the positively charged nucleus and the negatively charged electrons is weaker.

• Therefore, the valence electrons are further away from the nucleus, so the atomic radius is larger

atomic radius within a group

• As you move down a group, more energy levels are added.

• Each additional energy level is a greater distance from the nucleus.

• This occurs because the electrons of the inner levels shield the outer electrons from the full charge of the nucleus.

• As a result, the outer electrons are not as strongly attracted by the nucleus

• resulting in a larger atomic radius

Ionization energy

• the quantity of energy required to remove an electron from an atom or ion in the gaseous

• Increases on the periodic table (Left to right and up in a group)

Ionization energy across a row

As atomic radius decreases, the pull on the outermost electrons

increases and thus it is harder to remove them (it takes more

energy to do so)

Ionization Energy – Within a Group

The atomic radius decreases from bottom to top in a group. As

atomic radius decreases, the pull on the outermost electrons

increases and thus it is harder to remove them (it takes more

energy to do so).

Electron affinity

• the energy change that occurs when an electron is added to a neutral atom in the gaseous state

• Electron affinity increases on the periodic table (Left to right across a row and up in a group)

Trends summary