Acid Base Behavior Of Element Oxides

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What is the acid base behavior of element oxides? Information and examples about acid base behavior of some common oxides

Acid Base Behavior Of Element Oxides

The trend in acid-base behavior of element oxides. red = acidic; blue = basic)

Acid Base Behavior Of Element Oxides; Metals are also distinguished from nonmetals by the acid-base behavior of their oxides in water:

• Most main-group metals transfer electrons to oxygen, so their oxides are ionic. In water, these oxides act as bases, producing OH ions and reacting with acids. Calcium oxide is an example.

• Nonmetals share electrons with oxygen, so non-metal oxides are covalent. In water, they act as acids, producing H+ ions and reacting with bases. Tetraphosphorus decaoxide is an example.

Figure on the right classifies the acid-base behavior of some common oxides, focusing once again on the elements in Group 5A, dinitrogen pentaoxide, N2O5, forms nitric acid:

\displaystyle {{N}_{2}}{{O}_{5(s)}}+{{H}_{2}}{{O}_{\left( l \right)}}\to 2HN{{O}_{3\left( aq \right)}}

Tetraphosphorus decaoxide, P4O10, forms the weaker acid H3PO4:

\displaystyle {{P}_{4}}{{O}_{10(s)}}+6{{H}_{2}}{{O}_{\left( l \right)}}\to 4{{H}_{3}}P{{O}_{4(aq)}}

The oxide of the metalloid arsenic is weakly acidic, whereas that of the metalloid antimony is weakly basic. Bismuth, the most metallic of the group, forms a basic oxide that is insoluble in water but that forms a salt and water with acid:

\displaystyle B{{i}_{2}}{{O}_{3(s)}}+6HN{{O}_{3(aq)}}\to 2Bi{{\left( N{{O}_{3}} \right)}_{3(aq)}}+3{{H}_{2}}{{O}_{(l)}}

Note that as the elements become less metallic across a period, their oxides become more acidic. In Period 3, sodium and magnesium form the strongly basic oxides Na2O and MgO.

Some metals and many metalloids form oxides that are amphoteric: they can act as acids or as bases in water. Metallic aluminum forms amphoteric aluminum oxide (Al2O3), which reacts with acid or with base:

\displaystyle A{{l}_{2}}{{O}_{3(s)}}+6HC{{l}_{(aq)}}\to 2AlC{{l}_{3(aq)}}+3{{H}_{2}}{{O}_{(l)}}

\displaystyle A{{l}_{2}}{{O}_{3(s)}}+2NaO{{H}_{(aq)}}+3{{H}_{2}}{{O}_{(l)}}\to 2NaAl{{(OH)}_{4(aq)}}

Silicon dioxide is weakly acidic, forming a salt and water with base:

\displaystyle Si{{O}_{2(s)}}+2NaO{{H}_{(aq)}}\to N{{a}_{2}}Si{{O}_{3(aq)}}+{{H}_{2}}{{O}_{(l)}}

The common oxides of phosphorus, sulfur, and chlorine form acids of increasing strength: H3PO4, H2SO4, and HClO4.

So the metallic properties decreases from left to right across a period, and increases from top to bottom within a group Most of the periodic properties of elements are summarized in below.

Comparison of Periodic Properties in Periodic Table

1 Within period from left to right 1 Down a group from top to bottom
1. Atomic number increases. 1. Atomic number increases.
2. Mass number increases. 2. Mass number increases.
3. Atomic volume decreases. 3. Atomic volume increases.
4. lonazation energy increases. 4. lonazation energy decreases.
5. Electron affinity increases. 5. Electron affinity decreases.
6. Electron losing tendency decreases. 6. Electron losing tendency increases.
7. Metallic character decreases. 7. Metallic character increases.
8. Nonmetallic character increases. 8. Nonmetallic character decreases.
9. Acidic character of oxides increases. 9. Acidic character of oxides decreases.
10. Number of valence electrons increases. 10. Number of valence electrons does not change.

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