Azoto vs. nitrogénio vs. nitrogénio
The words azoto, nitrogénio, and nitrogênio all refer to the same chemical element (Atomic Number 7). The differences are strictly regional and orthographic. Azoto is a traditional term used in European Portuguese (Portugal), nitrogénio is an alternative European spelling, and nitrogênio is the standard spelling in Brazilian Portuguese.
Azoto
B2This is the most common term for nitrogen in European Portuguese (used in Portugal and African Lusophone countries). It stems from the French word azote. While scientific contexts in Portugal accept nitrogénio, usage of azoto remains widespread in textbooks, industry, and daily life.
O ar atmosférico é composto principalmente por azoto.
(Atmospheric air is composed mainly of nitrogen.)
Os mergulhadores devem ter cuidado com a narcose por azoto.
(Divers must be careful with nitrogen narcosis.)
O azoto líquido é frequentemente usado na conservação de alimentos.
(Liquid nitrogen is often used in food preservation.)
Esta fábrica produz fertilizantes à base de azoto para a agricultura.
(This factory produces nitrogen-based fertilizers for agriculture.)
Nitrogénio
B2This spelling features an acute accent (é) and is used in European Portuguese. It serves as a synonym for azoto. It is becoming more frequent in academic and scientific writing in Portugal to align with international nomenclature, but the pronunciation differs from the Brazilian version.
Na tabela periódica, o símbolo do nitrogénio é N.
(In the periodic table, the symbol for nitrogen is N.)
O ciclo do nitrogénio é vital para a sobrevivência dos ecossistemas.
(The nitrogen cycle is vital for the survival of ecosystems.)
Medimos a concentração de dióxido de nitrogénio na cidade.
(We measured the concentration of nitrogen dioxide in the city.)
As bases do ADN contêm átomos de nitrogénio.
(DNA bases contain nitrogen atoms.)
Nitrogénio
B2This is the exclusive term used in Brazilian Portuguese. It is spelled with a circumflex accent (ê) because the vowel sound is closed in the Brazilian accent. In Brazil, the word azoto is archaic and almost never used.
Alguns motoristas preferem encher os pneus com nitrogênio.
(Some drivers prefer to fill their tires with nitrogen.)
O médico usou nitrogênio líquido para remover a verruga.
(The doctor used liquid nitrogen to remove the wart.)
O nitrogênio é fundamental para a síntese de proteínas.
(Nitrogen is fundamental for protein synthesis.)
Houve um vazamento de gás nitrogênio no laboratório.
(There was a nitrogen gas leak in the laboratory.)
Summary
Use nitrogênio (with a circumflex) if you are speaking or writing for a Brazilian audience. Use azoto commonly in Portugal for general contexts, or nitrogénio (with an acute accent) for scientific contexts in Portugal. Do not use azoto in Brazil, as it likely will not be understood.