Question

How do you find out if an element has one or more than one valence electron, and what are some examples for each case?

Answer 1

To determine the number of valence electrons in an element, you need to examine its electron configuration. The electron configuration describes the distribution of electrons in the atom's energy levels or orbitals. The valence electrons are specifically the electrons in the outermost energy level.

Here are a few guidelines to determine the number of valence electrons:

1. For main group elements (s and p block elements), the number of valence electrons is equal to the group number. For example:

   • Group 1 elements (such as hydrogen, lithium, sodium) have one valence electron.
   • Group 2 elements (such as beryllium, magnesium, calcium) have two valence electrons.
   • Group 13 elements (such as boron, aluminum, gallium) have three valence electrons.
   • Group 14 elements (such as carbon, silicon, germanium) have four valence electrons.
   • Group 15 elements (such as nitrogen, phosphorus, arsenic) have five valence electrons.
   • Group 16 elements (such as oxygen, sulfur, selenium) have six valence electrons.
   • Group 17 elements (such as fluorine, chlorine, bromine) have seven valence electrons.
   • Group 18 elements (such as helium, neon, argon) have eight valence electrons (except helium, which has only two valence electrons).

2. For transition metals and inner transition metals, determining the number of valence electrons can be more complex as they involve the filling of d and f orbitals. The valence electrons for these elements are usually counted from the outermost s and d or s, d, and f orbitals.

Here are some examples:

• Sodium (Na) is in Group 1. Therefore, it has one valence electron.
• Oxygen (O) is in Group 16. Hence, it has six valence electrons.
• Aluminum (Al) is in Group 13, so it has three valence electrons.
• Chlorine (Cl) is in Group 17, giving it seven valence electrons.
• Calcium (Ca) is in Group 2, indicating it has two valence electrons.
• Iron (Fe) is a transition metal, and its valence electrons are counted from both the 4s and 3d orbitals. Iron can have two or three valence electrons, depending on its oxidation state in a particular compound.

Remember that the periodic table is a helpful tool for identifying the group number and determining the number of valence electrons for main group elements. For transition metals and inner transition metals, additional information about the electron configuration and oxidation states is needed to determine the exact number of valence electrons.