The document discusses key concepts in general chemistry including: 1) Effective nuclear charge increases left to right and down a period, lowering electron energy due to stronger electrostatic attraction but increasing it due to greater electron-electron repulsion. 2) Magnesium has an electron configuration of [Ne]3s2, with 2 valence electrons and an effective nuclear charge of +2. 3) Atomic radius generally decreases left to right and increases down a period, while ionic radius follows the opposite trends due to shielding effects.

1. KEY
GENERAL CHEMISTRY-II (1411)
S.I. # 29
1. Define effective nuclear charge:
A. Zeff represents the average electrical environment created by the nucleus and
the other electrons in the number of core electrons – 7.9
2. What is the trend of effective nuclear charge across the periodic table?
A. Nuclear charge increases left  right and results in an increase in Zeff.
7.9
3. How does the electrostatic attraction for the nucleus effect the energy of an
electron?
A. This lowers the energy of the electron. 7.10
4. How does electron-electron repulsion effect the energy of an electron?
A. This increases the energy of the electron 7.10
5. a. What is the electron configuration of Magnesium?
1s22s22p63s2 or [Ne] 3s2
b. How many valence electrons does Magnesium have? 2
c. What is the energy level of Magnesium?
The s-orbital has an energy level of l=0
d. What is the effective nuclear charge of Magnesium?
12(valence electrons) – 10(v.e. of previous noble gas) = +2 charge
e. Explain how it differs from the nuclear charge of Carbon.
Carbon = 1s22s22p2, energy level = l = 1 (p-orbital),
6 v.e. – 2 v.e. prev. noble gas = +4 charge
It has a higher energy level and nuclear charge as predicted by the
periodic trend. Section 7.2 pg 265
6. How do the sizes of atoms change as we move
a. from left to right across a row in the periodic table,
atomic radius decreases LR
b. from top to bottom in a group
increases from Top  Bottom
c. Arrange the following in order of increasing atomic radius: F, P, S,
As.

2. KEY
F < S < P < As 7.21
7. Arrange the following atoms in order of increasing atomic radius. Si, S, Ge, Se.
S < Si < Se < Ge atomic radius increases to the left and down a column. 7.22b
8. Why does the size of ions increase down a column in the periodic table?
A. the n value of the valence electrons increases and are farther from the nucleus.
Valence electrons also experience greater shielding by core electrons. 7.25c
9. a. List the atoms in order of increasing size: S, Cl and K
Cl < S < K
b. List the ions in order of increasing size.
K+ < Cl- < S2-
c. Explain any differences in the orders of atomic and ionic sizes.
K has the largest Z value, but the n-value of the outer electron is larger
than the n-value of valence electrons in S and Cl so K atoms are largest.
7.32
10. Write the equations that show the processes for
a. the first two ionization energies of tin and
1.Sn(g)  Sn+(g) + 1e-
2. Sn+  Sn2+(g) + 1e-
b. the fourth ionization energy of titanium
1. Ti3+(g)  Ti4+(g) + 1e-