1. 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
Increasing number of atomic number (number of protons)
Sometimes labeled 1-17 (just subract 10 from)

2. Periodic Trends

3. 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
Period 3 has 3 energy levels for electrons

4. Periodic Trends

5. 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

6. 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

7. Periodic Trends

8. 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)

9. Periodic Trends Na+ Mg2+ Al3+ P3- S2- Cl-
An example showing the relative ion sizes from Period 3 are shown below:
Na+ Mg Al P S 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

10. 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

11. 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 #)

12. 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