The vibration of the water molecule is composed of three normal modes. Two modes are stretching the molecule along the covalently bound O and H. The third is bending the entire molecule in the σ_v^xz reflection plane that is spanned by the three atoms, basically changing the angle α(H-O-H). The stretching mode ν₁(A₁) and the bending mode ν₂(A₁) are symmetric with respect to the σ_v^yz reflection plane, while the stretching mode ν₃(B₂) is antisymmetric. Water is in the C_2v point group with the symmetry elements: C₂ axis (black), σ_v^xz plane (cyan) and σ_v^yz plane (yellow). [check symotter-gallery]