AP BIOLOGY

Detailed explanation-1: -Atoms tend to be stable and nonreactive if they have 6 valence electrons. In the periodic table, the number of valence electrons in each element decreases from left to right across each period.

Detailed explanation-2: -Group 16 elements with six valence electrons are almost as reactive for the same reason. Atoms of group 18 elements have eight valence electrons (or two in the case of helium). These elements already have a full outer energy level, so they are very stable.

Detailed explanation-3: -The valence electrons of an atom are those electrons that have the highest energy. Valence electrons are involved in chemical bonding. The number of valence electrons in each atom helps determine the chemical properties of that element. Electron Dot Diagram – includes the symbol for the element surrounded by dots.

Detailed explanation-4: -An atom is most stable if its outermost energy level contains as many electrons as it can hold. For example, helium has two electrons, both in the first energy level. This energy level can hold only two electrons, so helium’s only energy level is full. This makes helium a very stable element.

Detailed explanation-5: -In this table, you can see that helium has a full valence shell, with two electrons in its first and only, 1n, shell. Similarly, neon has a complete outer 2n shell containing eight electrons. These electron configurations make helium and neon very stable.