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.

All these elements are chemically stable by themselves. It is only in the presence of other elements that they are chemically reactive.

Atom   Group  Valence electrons Reactivity

1) Mg        2                     2                Fairly reactive

2) Cs        1                      1                 Highly reactive

3) Ne      18                     8                Completely unreactive

4) C        14                      4                Relatively unreactive

5) Kr       18                      8                Almost completely unreactive

Cs is the most reactive element because it needs to lose only one valence electron to get a stable octet.

Mg is less reactive than Cs because it must lose two valence electrons to get a stable octet.

C is relatively unreactive because it must either lose or gain four valence electrons to get a stable octet.

Ne is completely unreactive because it already has a stable octet.

Kr also has a stable octet, but its valence electrons are so far from the nucleus that some highly reactive elements will react with it.

c. is the answer

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