Homework 31

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Q 4.5, 5.48

Q 4.50

Question: Elements can be identified by their electron configuration and referencing it to the periodic table. Identify each element below based on their electron configurations.

A. [Ne]3s²3p²

B. [Ne]3s²3p⁶

C. [Kr]5s¹

C. [Kr]5s²4d¹⁰5p³

Solution:

Strategy:

Identify the noble gas and the row in which it lies within the periodic table. This represents the inner electron configuration which is represented by [noble gas symbol].
Move down one row below the aforementioned period to then use the outer electron configuration, namely the configuration after [noble gas symbol], to identify the element.
Move across the row, moving from left to right, assigning the electrons within the outer electron configuration to the appropriate orbitals, s, p, d, and f orbitals, to identify the element. For example, an element with [He]2s²2p⁴ will have 2 electrons in the 2s orbital and 4 electrons in the 2p orbitals and as you move across period 2, it will correspond to oxygen (O).

A. Si

B. Ar

C. Rb

D. Sb

Q 5.48

Question: Write four different ionic compounds that can be formed using the following elements:

Sodium, Chlorine, Aluminium and Sulfur.

Solution:

Strategy:

Identify which elements are the metals and which are the nonmetals that will be arranged to form the ionic compounds.
Ionic compounds always contain positive and negative ions; therefore identify the positive charge of each metal identified in the above step and the negative charge of each nonmetal identified in the above step using the periodic table for reference. http://chemwiki.ucdavis.edu/Reference/Periodic_Table_of_the_Elements
Combine each metal with each nonmetal to form the initial foundation for the ionic compound. The sum of the positive charges must equal the sum of the negative charges within the compound which means that the number of each ion may have to be adjusted to achieve the balance of ions. If so, then the formula of the ionic compound will always reflect the smallest whole number ratio of ions. For example: 2:1, 2:3, etc.

NaCl

Na₂S

AlCl₃

Al₂S₃