1st energy level can hold 2 electrons
2nd energy level can hold 8 electrons
3rd energy level can hold 8 or 18 electrons
Control rods are used<span> in </span>nuclear<span> reactors to </span>control<span> the fission rate of uranium and plutonium. They are composed of chemical elements such as boron, silver, indium and cadmium that are capable of absorbing many neutrons without themselves fissioning.</span>
Fossil C is the youngest. Layers further down were placed earlier than others. Because C is on the top layer, it must be the youngest (unless a disaster mixed up all the layers!).
What the question there is nun
Silicon dioxide is SiO2. Silicon has 4 valence electrons, while each oxygen has 6 valence electrons. This can be shown as
** * *
** O * * Si * * O **
* * **
At points where there is one valence electron, represented by a lone *, the electrons will be 'shared' between the atoms. This will make silicon dioxide appear as
** *--------------- *
** O *--* Si * ------ * O **
*------- * **
, as the lines with no arrows indicate that each electron moves between the atoms, and does not stay with one forever.
