What is the electron shielding effect? What is the trend for it? How and why does it happen?

The density of water is 1 g/cm cubed and in order for the pebble to sink its density has to be greater than the density of water and in order for the twig to float its density has to be less than the density of water

For lesson: cameras, plant presses, newspaper, paper towels, clip boards, pencils, calculators, field guides, metric measuring tapes, paper, transect squares, colored pencils, ph meters, light meters, computers, etc.for extension: baggies for soil samples collecting, distilled water, hand shovels, beakers, boiled rice, microscopes, well microscope slides or regular microscope slides with cover slips

Firstly, the planetary model of the atom  failed  to explain why individual atoms produce discrete  line spectra. in fact, according to rutherford's model, each individual atom should produce a  continuous  line spectrum. the second flaw to his model was the fact that electrons orbit the nucleus in a circular fashion.