Orbital overlap was an idea first introduced by Linus Pauling to explain the molecular bond angles observed through experimentation and is the basis for the concept of orbital hybridisation. s orbitals are spherical and have no directionality while p orbitals are oriented 90° to one another. A theory was needed therefore to explain why molecules such as methane (CH4) had observed bond angles of 109.5°.[1] Pauling's theory was that bonds are created by the overlap of adjacent atomic orbitals of two atoms. The greater the overlap of the two orbitals, the stronger the bond. The resulting bond is known as an sp hybrid and it exhibits strength greater than that of an s or p orbital.[2]