We define the Anderson hamiltonian on the two dimensional torus $\mathbb R^2/\mathbb Z^2$. This operator is formally defined as $\mathscr H:= -Δ+ ξ$ where $Δ$ is the Laplacian operator and where $ξ$ belongs to a general class of singular potential which includes the Gaussian white noise distribution. We use the notion of paracontrolled distribution as introduced by Gubinelli, Imkeller and Perkowski in [14]. We are able to define the Schrödinger operator $\mathscr H$ as an unbounded self-adjoint operator on $L^2(\mathbb T^2)$ and we prove that its real spectrum is discrete with no accumulation points for a general class of singular potential $ξ$. We also establish that the spectrum is a continuous function of a sort of enhancement $Ξ(ξ)$ of the potential $ξ$. As an application, we prove that a correctly renormalized smooth approximations $\mathscr H_\varepsilon:= -Δ+ ξ_\varepsilon+c_\varepsilon$ (where $ξ_\varepsilon$ is a smooth mollification of the Gaussian white noise $ξ$ and $c_\varepsilon$ an explicit diverging renormalization constant) converge in the sense of the resolvent towards the singular operator $\mathscr H$. In the case of a Gaussian white noise $ξ$, we obtain exponential tail bounds for the minimal eigenvalue (sometimes called ground state) of the operator $\mathscr H$ as well as its order of magnitude $\log L$ when the operator is considered on a large box $\mathbb T_L:= \mathbb R^2/(L\mathbb Z)^2$ with $L\to \infty$.