# What is an 'acidic' oxide?

My book says that:

Oxides in higher oxidation states of elements of group 14 are generally more acidic than those in lower oxidation states.The dioxides $\ce{CO2}$, $\ce{SiO2}$ and $\ce{GeO2}$ are acidic whereas $\ce{SnO2}$ and $\ce{PbO2}$ are amphoteric in nature. Among monoxides, $\ce{CO}$ is neutral, $\ce{GeO}$ is distinctly acidic whereas $\ce{SnO}$ and $\ce{PbO}$ are amphoteric.

1. First and foremost:
How can an oxide be acidic? Is it because of their reactions with other compounds? I know about Arrhenius, Lewis and Bronsted acids and bases but still can't seem to connect!

2. Secondly, why does the book say "Oxides in higher oxidation states of elements of group 14 are generally more acidic than those in lower oxidation states"? Is there a logical reason behind this?

3. Is the trend mentioned in the second question followed by all groups of the periodic table and not just for group 14?

By 'all groups', I am referring to s and p block elements. I don't know much about the chemistry of the d and f block elements - I will study them in a few weeks time, but I reckon they should also follow this trend.

• The word "acidic" in "acidic oxide" means that the hydrated form of the said oxide is an acid. It does not mean that the oxide itself is an acid either by Arrhenius, by Bronsted, or by Lewis. – Ivan Neretin Nov 13 '15 at 11:32
• – Mithoron Nov 13 '15 at 12:23
• Book is wrong about GeO unless it/you meant GeO2. en.m.wikipedia.org/wiki/Germanium_monoxide is reported as amphoteric. – Oscar Lanzi Dec 3 '17 at 22:09
• @Ivan you may be right but usually an acidic oxide is, or as it reacts it generates, a Lewis acid. – Oscar Lanzi Dec 3 '17 at 22:17

1. Oxides are acidic or basic based on their reaction with a base or an acid. Here, in group 14 elements, $\ce{CO2}$ is acidic ie; it reacts with a base. When the oxides are amphoteric, they react with both acids and bases.