chem: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/chem - from package: groff

You may install the required package with command apt-get install {package}

Error in other languages:
chem: bevel nie gevind nie
chem: comandă negăsită
chem: comando não encontrado
chem: commande introuvable
chem: command not found
chem: käsku ei ole
chem: không tìm thấy lệnh
chem: komanda nerasta
chem: Kommando nicht gefunden.
chem: kommandot finns inte
chem: komut yok
chem: nie znaleziono polecenia
chem: níor aimsíodh an t-ordú
chem: no se encontró la orden
chem: no s'ha trobat l'ordre
chem: opdracht niet gevonden
chem: parancs nem található
chem: perintah tidak ditemukan
chem: príkaz nenájdený
chem: příkaz nenalezen
chem: команда не найдена
chem: командата не е открита
chem: 命令找不到
chem: コマンドが見つかりません