Final answer:
The pattern of Bohr model structures of the first 18 elements follows a specific order of electron filling. Columns in the periodic table are called groups, and the rows are called periods. Elements in the same group exhibit similar chemical characteristics.
Step-by-step explanation:
The pattern of the Bohr model structures of the first 18 elements can be described by understanding the filling order of electrons in the atom. The Bohr model provides a simplified representation of electron distribution in orbitals around the nucleus. In the fourth row and beyond, the order of electron filling deviates from the expected pattern due to electron interactions. The columns in the periodic table are called groups and the rows are called periods. Elements with similar chemistry are grouped together in vertical columns, and each row represents the number of electron shells the elements have.