1. Periodic Trends

2. Describe factors that affect electron position around a nucleus.
Include: nuclear charge, distance, shielding.
Explain periodic trends using above factors.
Include: atomic / ionic radii, ionization energy, electronegativity.

3. The force on an electron will affect its position around the atom
The force on an electron will affect its position around the atom. The force depends on 3 factors:
Nuclear charge - more protons, more attraction.
Distance – further apart two charges are, lower their force of attraction (Coulomb’s Law).
Shielding Effect - Inner electrons shield the force of the nucleus from outer electrons.

4. ATOMIC RADIUS
Size of atoms tends to vary from substance to substance due to different interaction.
Measured as half the distance between two nuclei when two like atoms are bonded together.

5. Decrease Across
same quantum level (same size / n value)
increase in nuclear charge ( pulls orbitals closer)
Increase Down
new quantum level (larger size / n value)
increased shielding (decreased force on outer e-)

6. Na:
11 p+
11 e-
Cl:
17 e-
17 p+

7. IONIC RADIUS
Ion size differs from atom size.

8. *Same* basic trend as atomic radius.

9. Positive ions - smaller radii
increased proton - electron balance (lost e-)
more nuclear charge on remaining e-
sometimes loss of a quantum level.
Negative ions - bigger radii
decreased proton - electron balance (gain e-)
Less nuclear charge on remaining e-
repulsion of additional e- causes expansion.

10. + - Na Cl

11. A(g) + energy → A+(g) + e−
Ionization Energy
Energy required to remove an electron from an atom forming an ion – energy depends on force on e-.
A(g) + energy → A+(g) + e−
There are multiple ionization energy values for each element – one for each electron being removed.
A+(g) + energy → A+2(g) + e−

12. Increases Across
increased nuclear charge (increasing p+ number)
same quantum level
Decreases Down
new quantum levels (increased distance)
increased shielding (decreases force on outer e-)

13. + Na Cl

14. Na Cs

15. IE increases with each electron removed
Increased proton-electron ratio (small change)
Less shielding (small change)
Lower quantum level – closer (BIG change)

16. Electronegativity
Attraction an atom has for bonding electrons.
bigger the number, the harder they pull
Periodic Trend:
EN increases across the table and decreases down.

17. Na: Cl: WEAKER nuclear charge. STRONGER nuclear charge.
Less attraction - large radius.
STRONGER nuclear charge.
More attraction - small radius.
Na:
Cl:
Lower ionization energy.
Lower Electronegativity.
HIGHER ionization energy.
HIGHER Electronegativity.

18. - + Large enough difference – ionic bonds form.
The greater the electronegativity difference the more polar the bond. δ- δ+ H C H Cl H
Polar covalent
non-polar covalent
Large enough difference – ionic bonds form. - +

19. EN Difference
Bond Type
Percent Ionic
less than 0.4
non-polar covalent
0% − 5%
0.4 − 1.9
polar covalent
5% − 60%
greater than 1.9
ionic
> 60%

21. CAN YOU / HAVE YOU?
Describe factors that affect electron position around a nucleus.
Include: nuclear charge, distance, shielding.
Explain periodic trends using above factors.
Include: atomic / ionic radii, ionization energy, electronegativity.