code: def get_period(atom_z: int) -> int:
      """get the period of the given atom z
  
      Examples
      --------
      >>> from deepchem.utils import get_period
      >>> atom_number = 13
      >>> get_period(atom_number)
      3
  
      Parameters
      ----------
      atom_z: int
          Atomic Number of the Element.
  
      Returns
      -------
      period: int
          Period of the Element.
  
      References
      ----------
      Kasim, Muhammad F., and Sam M. Vinko. "Learning the exchange-correlation
      functional from nature with fully differentiable density functional
      theory." Physical Review Letters 127.12 (2021): 126403.
      https://github.com/diffqc/dqc/blob/master/dqc/utils/periodictable.py
  
      """
      period: int = 0
  
      if atom_z <= 2:
          period = 1
      elif atom_z <= 10:
          period = 2
      elif atom_z <= 18:
          period = 3
      elif atom_z <= 36:
          period = 4
      elif atom_z <= 54:
          period = 5
      elif atom_z <= 86:
          period = 6
      elif atom_z <= 118:
          period = 7
      else:
          raise RuntimeError("Unimplemented atomz: %d" % atom_z)
  
      return period
  
imports: from typing import Union
  import numpy
  import torch
label_desc: Use image node_id 3 for calling a global function with example usage: get_period(atom_z) and returns: period