\(\left\{{}\begin{matrix}P+N+E=18\\P=E\\P\le N\le1,5P\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}2P+N=18\\P\le N\le1,5P\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}N=18-2P\\P\le18-2P\le1,5P\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}N=18-2P\\3P\le18\le3,5P\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}N=18-2P\\6\ge P\ge5,143\end{matrix}\right.\\ \Leftrightarrow\left\{{}\begin{matrix}P=E=6\\N=18-2P=6\end{matrix}\right.\\ A=P+N=6+6=12\left(đ.v.C\right)\)
Tên nguyên tố: Cacbon
Khối lượng nguyên tử:
\(m=6.m_N+6.m_P+6.m_E\\ =6.\left(9,1094.10^{-31}+1,6726.10^{-27}+1,6748.10^{-27}\right)\\ \approx2,00899.10^{-26}\left(kg\right)\)
Ta có : \(Z\le N\le1,5Z\)
=> \(3Z\le2Z+N\le3,5Z\)
=> \(5,14\le Z\le6\)
=> Z=6= P=E
=> X là Cacbon (C)
=> N=18-6.2=6
mC =6. 9,109.10-31 + 6.1,6726.10-27 + 6.1,6748.10-27 = 2.10-26kg
