I actually use Fedora, so the
.desktop and other file paths may probably be different in Ubuntu.
OBS: This is similar to other answers, but it differs because by following the instructions below you will you have an app-like experience instead of a regular chrome window.
Anyway, the idea is essentially the same: You can create a file named
chome-whataspp.desktop on your
.local/share/applications/ directory that launches chrome in the app mode (a separate window, with no tabs and that act as a desktop app. Even the tray icon will show as the whatsapp logo istead of chrome's icon).
OBS: You'll need to download a png Whatsapp logo (not for the tray, which is loaded from the web page, but for the launcher). This is easy to find one with a transparent background in google images.
Icon=<path to a png logo file, (e.g. /home/<user>/Icons/WhatsApp.png)>
Icon[C]=<path to a png logo file, (e.g. /home/<user>/Icons/WhatsApp.png)>
Comment[C]=WhatsApp (chrome in app mode)
Comment=Direct link to WhatsApp web in chrome app mode