The outer energy level for this atom is n = 3, and it has two electrons in this energy level. Therefore, magnesium has two valence electrons. It holds six electrons, so sulfur has six valence electrons.

2 Answers. Most transition metals have 2 valence electrons. Valence electrons are the sum total of all the electrons in the highest energy level (principal quantum number n). Most transition metals have an electron configuration that is ns2(n−1)d , so those ns2 electrons are the valence electrons.

The transition metals are a group of elements in the periodic table. They make up the largest section of the periodic table located at the center of the table including columns 3 through 12.

Magnesium loses two electrons to form Mg2+, and oxygen gains two electrons to form O2−.

If atoms gain electrons, they become negative ions, or anions. Consider the example of fluorine (see figure below). A fluorine atom has nine protons and nine electrons, so it is electrically neutral. If a fluorine atom gains an electron, it becomes a fluoride ion with an electric charge of -1.

Groups 5,6,7 contain non-metals and they gain electrons (e-) to make stable ions.

Electrons and the Periodic Table

Fluorine has an atomic number of 9 and so therefore in a neutral state, one atom of fluorine has 9 protons and 9 electrons. So if our ‘mystery’ element has 10 electrons, it must also have 10 protons. The number of protons in an atom is given by its Atomic Number in the periodic table.

Fluorine is in Group 7. It has seven electrons in its outer shell. It gains an electron from another atom in reactions, forming a fluoride ion, F -. Note that the atom is called fluorine, but the ion is called fluoride.