Describe what it means if a chemical or physical property is periodic

The car hoist allows the car to be driven onto the platform, after which the rear wheels are raised. if the loading from both rear wheels is 1380 lb, determine the force in the hydraulic cylinder ab. neglect the weight of the platform itself. member bcd is a right-angle bell crank pinned to the ramp at c. the force is positive if in tension, negative if in compression.

Will you chech and finish these for me, because i am stumped with them.

What structural formula represents 4 electrons shared between two atoms?