CAS is the Chemical Abstracts Service. In the CAS system the letters A and B were designated to main group elements (A) and transition elements (B). Though the IUPAC numeration is the official, the CAS numeration is what is still used in classrooms and laboratories.
Mostrar CAS: O CAS é a Chemical Abstracts Service. No sistema CAS designáronse as letras A e B para o grupo principal de elementos (A) e para os elementos de transición (B). Apesar de que a numeración IUPAC é a oficial, a do CAS aínda é usada en aulas e laboratorios.