Tutor profile: Alicia G.
Subject: Inorganic Chemistry
Define the term "diagonal relationship" and give two examples of Be and Al exhibiting such a relationship.
The diagonal relationship is a periodic trend describing similar properties between an element in the upper-left corner of the periodic table and the element to its lower right: lithium and magnesium; beryllium and aluminum; and boron and silicon. As an example, Be and Al are both amphoteric and form parallel anions with concentrated hydroxide ion. Additionally, both Be and Al form carbides containing the C^4- ion.
How can you tell whether a reaction is spontaneous or non-spontaneous at room temperature?
To tell whether a reaction is spontaneous or non-spontaneous at room temperature, you need to find the Gibbs' Free Energy, which takes into account the balance between entropy and enthalpy. Entropy is a measure of the disorder; reactions which create more disorder - have a positive entropy - tend to be favored (spontaneous). Enthalpy is a measure of the energy of a system, which prefers to have a minimum value, so that reactions with negative enthalpy tend to be favored (spontaneous). Gibbs Free Energy - the energy available to do useful work - calculates the balance between these two, sometimes opposing factors and taking into account the temperature of the reaction. If Gibbs Free Energy is negative at a given temperature, the reaction will be spontaneous at that temperature. If it is positive, then the reaction will be non-spontaneous at that temperature.
Subject: Basic Chemistry
How do the charges of the monatomic ions of the elements change as you go across a row of the periodic table, and why do they follow this trend?
As you go across the periodic table from left to right, the charges of the metals increase by one, corresponding to the group number. For the nonmetals, the charges are negative and correspond to 8 minus the group number, increasing by one from left to right. Ions form by losing or gaining electrons in order to reach the noble gas configuration of 8 electrons in the valence shell. Metals will lose electrons since they have fewer electrons in their valence shells, giving a positive ion (cation). Nonmetals will gain electrons to give a negative ion (anion). The number needed to be gained or lost is simply how many columns away that element is from the nearest noble gas.
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