Classification of Elements & Periodicity in Properties Test 3

The rows of the periodic table are called periods, while the columns of the table are called groups.

The Russian scientist Dmitri Mendeleev proposed a periodic table similar to the one we use today in 1869. He arranged the elements according to "periodic law", where element properties could be predicted based on recurring similarities between elements (periodicity).

The modern periodic table orders elements by increasing atomic number, which is the number of protons in the atom of the element. Mendeleev did not know about the parts of the atom, so he used the next best thing -- atomic weight.

Even though each atom has more electrons as you move from left to right across the periodic table, the atomic radius decreases. The reason is that you're also adding more protons, which exert a stronger attractive force on the electrons, drawing them in a tiny bit closer. Ionic radius also decreases, although not for the exact same reason.

As you move down a periodic table group, electronegativity decreases because the distance between the atomic nucleus and the valence electrons increases.

There are several ways to tell metals and nonmetals apart. Nonmetalsdon't have a metallic appearance. Unlike metals, they typically have lower melting and boiling points and tend not to conduct heat or electricity very well.

 About 75% of the elements on the periodic table are metals. The only groups that are not metals are the noble gases, halogens, and the group actually called nonmetals.

Helium is the smallest atom. The energy level of the electrons determine the atom's volume. Electrons have a negative charge and the nucleus is positive since it is made up of protons and neutrons. Helium and Hydrogen have one and two electrons. This means they are in the the first energy sub level which is 1S (It can hold up to two electrons) So if that's all we were to consider, both atoms would be the same size. However, since Helium has more protons and electrons, the electrons have a greater attraction to the nucleus, thus decreasing its volume. So it is wrong to just look at atomic number. Hydrogen is not the smallest atom, it is the second smallest and Helium is the smallest.

In order for an atom to have a high electron affinity, it needs to be in a position to accept electrons. The alkaline earth metals (like calcium and magnesium) have filled s subshells, so they are stable. If anything, the alkaline earths prefer to lose electrons and exist as cations.

The correct answer is B
Halogens have maximum negative electron gain enthalpy in the corresponding periods. This is due to the fact that the atoms of these elements have only one electron less than stable noble gas configurations. Electrons gain enthalpy of the elements of the group becomes less negative down the group. However, the negative electron gain enthalpy of fluorine.