1. Trends in the Periodic Table
Chemistry 11
Ms. McGrath

2. Atomic Radius – Group Trends
As we move from left to right across a period the atomic radius of the atoms decrease
This is not what we expect…Why? As we go from left to right each additional electron is going into the same energy level. These electrons are the same distance away from the nucleus. At the same time, as we move from left to right, the protons are being added to the nucleus thus increasing the nuclear charge. As this happens electrons are being drawn to the nucleus and the size decreases.

3. Atomic Radius – Group Trends
As we move from the top of a group to the bottom, the atomic radii increase
This happens because, as we move from top to bottom the electrons are being placed into higher energy levels that place the electrons farther from the nucleus. Even though the nuclear charge is also increasing it is less effective at attracting electrons which are farther away from the nucleus.

4. What is Ionization Energy?
The energy required to remove an electron completely from an atom
(aka: the first ionization energy)

5. What is Ionization Energy?
Note: particles having the same energy level populations (the same number of electrons) as its closest noble gas are referred to isoelectronic

6. Ionization Energy – Period Trends
The ionization energy generally increases as we move from left to right across a period
This is due to the positive nuclear charge increasing as we move from left to right, it is more difficult to remove electrons when the nuclear charge is greater

7. Ionization Energy – Group Trends
The ionization energy generally increases as we move up a group
The outermost electrons of the smallest atoms of a group are closer to the nucleus and are more tightly held than the outer electrons of a larger atom

8. What is Electronegativity?
A quantitative measure of the electron-attraction ability of the atoms in a molecule
The bigger the electronegativity, the greater is the tendency of an atom to attract a shared pair of electrons

9. Electronegativity - Trends
The variation of electronegativity parallels the variation of ionization energies
As we move left (the metals) to the right (the non-metals) the electronegativity increases
As we go from top to bottom in a group, the electronegativity decreases

10. Bond Type and Electronegativity (pages 176 and 177)
For your notes define:
nonpolar covalent bond
polar covalent bond
bond dipole

11. Bond Type and Electronegativity
The differences of electronegativity between two atoms determine the types of bond between the two atoms.
If ∆EN is >1.7 – 3.3 the bond is mostly ionic
If ∆EN is >0.5 – 1.7 the bond is polar covalent
If ∆EN is >0 – 0.5 the bond is slightly polar covalent
If ∆EN is 0 the bond non-polar covalent
See page 177

12. Review Questions Give an example of each type of bond.
How do electronegativity values help predict whether a bond is pure covalent, polar covalent or ionic?
What is a double covalent bond? What is a triple covalent bond? Use an example for each to explain your answer.
Draw the Lewis structure for H2S and C2HBr.