Question

Give the number of valence electrons in the following elements and identify the element’s reactivity (chemically stable or unstable).

1) Magnesium, Mg

2) Cesium, Cs

3) Neon, Ne

4) Carbon, C

5) Krypton, Kr

EXAMPLE Response for one element: Calcium, Ca has 2 valence electrons and is chemically unstable.

Answer 1

Answer:

Element  Valence electrons   Stability

1)  Mg                    2                  Unstable

2) Cs                      1                  Highly unstable

3) Ne                     8                  Stable

4) C                        4                  Stable

5) Kr                       8                  Stable

Explanation:

Elements with eight valence electrons (the noble gases) are stable because they already have a complete valence shell.

Elements with one valence electron (the alkali metals) are highly unstable because they can easily lose one electron to reach a stable configuration.

Elements with two valence electrons (the alkaline earth metals) are unstable because they need to lose only two electrons to reach a stable configuration.

Carbon would have to either lose or gain four valence electrons to form an ionic compound. Instead, the atoms join to form stable ring systems with covalent bonds.