The answer is 0.62g. Solution: From year 1960 to year 2030, it has been 2030-1960 = 70 years
The half-life of the radioactive element is 28 years, then the sample will go through 70 years * (1 half-life/28 years) = 2.5 half-lives
Starting with a 3.5 gram sample, we will have 3.5*(1/2) after one half-life passes 3.5*(1/2) * (1/2) = 3.5*(1/4) after two half-lives pass 3.5*(1/4) * (1/2) = 3.5*(1/8) after three half-lives pass and so on
Therefore, we can write the remaining amount of the sample after the number n of half-lives have passed as mass of sample = initial mass of sample/2^n
The mass of the remaining sample for n = 2.5half-lives can be now calculated as mass of sample = 3.5 grams / 2^2.5 = 0.62 g
Electrons travel around the nucleus in circular orbits and moves from one orbit to another orbit when they absorb energy or lose energy. The Bohr atom is the model currently accepted for electrons in atoms because this model provides the right information about presence of electrons around the orbits. Scientists know the energies of electrons as well as the areas (orbitals) where the electrons are probably located with the help of new technology.
A cation is a positively charged ion, while an anion is a negatively charged ion. Contrary to how it sounds, when an atom loses electrons, it's charge becomes more positive. Since the calcium atom lost 2 electrons, it is a positive (+2) ion.
