Answer to Question #60333 in General Chemistry for Hafsa

Question

1. If an element has 12 protons and 17 neutrons, how many electrons must it have?

2. Why are the atomic masses of elements usually decimal numbers? Provide an answer using 3 – 4 sentences in your own words.


3. In 3 – 4 sentences and in your own words describe how Mendeleev’s periodic table differs from Moseley’s.

Answer 1

1. The answer is 12 because every atom or molecule must be neutral, so number of protons must be equal to number of electrons in atom.
2. As we know, one atom has a lot of nuclides(isotopes). Isotopes are the variants of particular chemical element which differ in neutron number, although all isotopes of a given element have the same number of protons in each atom, so different isotopes of one element have different masses. The mass in periodic table is an average value of mass of the all stable isotopes.
3. Mendeleev believed that the main characteristic of the element is its mass. The elements in his table were arranged in ascending order by mass. Because of this, in some places, the frequency was not carried out, for example iodine has less mass than tellurium, but on the properties it is halogen. Henry Moseley showed that the main characteristic of the element is its charge, then the periodic law was reformulated and elements arranged in order of increasing nuclear charge.