Periodic Trends• Periodic Table is arranged by:– Atomic number – Groups• Verticle column of the periodic table• Elements in the same group have similar physical &

chemical properties• Each group number will give you the number of valance

electrons

Periodic Trends

Periodic Trends

– Periods• Horizontal row of the periodic table • Physical and chemical properties change gradually

across a period• Period will indicate number of energy levels around the

nucleus

Periodic Trends

Periodic Trends

• Atomic Radius– Distance from the nucleus to the outer most

electron– Because we don’t know exactly where the

electrons are we say it is ½ the distance between 2 bonded atoms of the same element

Periodic Trends • Atomic radius will increase as we go down a

group– Number of energy levels increases – Outer electron is further from the nucleus which

means radius will increase • Atomic radius will decrease we go across a

period– Elements will have the same energy level but will

have an increased number of protons (atomic #)– More protons (+) attracts the electrons (-) in the

energy level bringing it closer to the nucleus and therefore decreasing the atomic radius

Periodic Trends

Periodic Trends

• Ionic Radius– Like atomic radius, it will increase in size as we go

down a group because of increase in electron shells

– However, across a period ionic radius will decrease (group 1-3) then increase (group 5) and decreases again (group 6-7)

Periodic Trends• An example showing the relative ion sizes from Period

3 are shown below: Na+ Mg2+ Al3+ P3- S2- Cl-

• The cations decrease in size because because there are fewer electrons than protons and therefore a strong pull towards the nucleus

• The anions are larger in size because there are more electrons than protons but because the atomic number increases (# of protons) and the electrons stay the same the radius will increase

Periodic Trends

• The size of an atom always decreases when being converted to a positive ion because it loses an electron and therefore there is less electron repulsion

• The size of an atom always increases when being converted to a negative ion because there is an increase in repulsion between electrons

Periodic Trends• Electronegativity– Measures the attraction an atom has for a shared pair

of electrons when it is covalently bonded

– Electronegativity decreases as you down a group• Due to shielding effect where electrons in a lower level

(closer to the nucleus) shield the positive charge from the nucleus and therefore the shells are not bound as tightly

– Electronegativity increases as you move across a period• Due to increase in protons (atomic #)

Periodic Trends• Ionization Energy– Amount of energy required to remove the outermost

electrons– Related to electronegativity

– Ionization energy decreases as you go down a group• Due to shielding effect which makes it easier to remove outer

electrons that have many atoms (near the bottom of the periodic table)

– Ionization energy increases as you move across a period• Due to increased nuclear charge which holds the electrons more

strongly