February 20, 2014
Wikispaces ISU
Jigmay Lungkara
Effective Nuclear Charge (ENC) and Shielding
*The force of attraction between positively charged protons and the negatively charged
electrons is the force that holds atoms together.
The electron shielding effect: is the effect where core electrons block valence electrons from
the nuclear charge of the nucleus, the canceling of the positive nuclear charge is called Shielding
Effect.
Effective Nuclear charge: is the net force experienced by an electron in an atom due to the
positively charged nucleas.
Equation for effective nuclear charge:
Zeff = Z - S
Z= # of protons in the nucleus
S=inner-shell electrons
or: ENC=Number of Protons - Number of inner electrons.
Example of ENC:
Effective Nuclear Charge (ENC) And Shielding
Equation: Zeff = Z - S
Element
# of
electrons
# of
valence
electrons
# of
protons
# of inner
electrons
ENC
Na
11
Mg
12
Al
13
Si
14
P
15
S
16
Cl
17
Ar
18
1
2
2
4
5
6
7
8
11
12
13
14
15
16
17
18
10
10
10
10
10
10
10
10
1
2
2
4
5
6
7
8
Reactivity of Non-metals
Reactivity - how easily a substance reacts with another.
*Metals lose electrons (Ionization Energy).
*Non-metals gain electron (Electron Affinity)
Ionization energy- The quality of energy required to remove an electron from an atom or ion in
a gaseous state. (Pg# 38)
General ionization equation: X(g) + energy = X+(g) + eElectron affinity: the energy change that occurs when an electron is added to a neutral atom in
the gaseous state. (pg# 40) General electron affinity equation: X(g) + e- = X-(g) + energy
Diagram on textbook page #41
AGENDA


Handouts: Properties of atom, and Trends in the periodic table summary sheet

Text: pg 36-41- Trends parameters and definitions
HW: finish all work sheets, pg 47 1-18; question # 1-19, 31; pg 48 # 47,55-57,6569
Websites recommended

http://www.youtube.com/watch?v=IvSmfgxCSNQ
 https://www.boundless.com/chemistry/periodic-properties/electronconfiguration/the-shielding-effect-and-effective-nuclear-charge/