According to the chemical composition of the layers of the Earth's internal structure, the order we see it with the outermost portion (least dense portion) first is

From Outermost portion,

The Crust( Continental and Oceanic)

The Mantle( Upper and Lower)

The Core ( Inner and outer)

Explanation:

The order which  we see it  the chemical composition  of the Earth's internal structure from  the outermost portion  is

A) The Crust--- The crust is the outermost, thinnest and  least dense layer of the  Earth's internal structure  and comprises of two types ; The continental ( consists of igneous, sedimentary and metamorphic rocks around the mountain regions  and the oceanic crust ( commonly basalt  around the ocean basin.The common  elements found here  are oxygen, silicon, aluminum, iron, and calcium. Thickness ranges from about 32 km to  8 km.

B) The Mantle:  This is the second layer of the internal structure consisting of the Upper and Lower mantle of which the Upper is made up of tectonic plates and responsible for the  formation of volcanoes, mountains, or earthquakes. After the Upper mantle , there is a transition zone which separates the two zones before reaching the lower mantle which is responsible for rising of the convection currents to carry heat from the internal part  of the earth to rise to the surface due to its extremely high temperature and pressure. Here ,the common elements consists of iron-magnesium-silicate. Density ranges from about 3400 kg/m3 to about  4400 kg/m3 and thickness from about 400 km to about 2,400km.

C) The Core: This is the center of the earth and the hottest part too. it comprises of the outer core(in liquid state, due to its lower pressure  with abundance of  iron and nickel, and inner core( In solid state, due to its extremely high pressure  and temperature with elements   iron and nickel together with other metals such as gold, platinum, palladium, silver, and tungsten). Its density ranges from  9,900kg/m3-  13,000 kg/m3.

a time line cause it goes from 685 to 978