# What would you expect the combining ratio to be for alkali metals to be with a halogen? With oxygen?

Mar 10, 2017

The combining ratio for alkali metals and halogens is $1 : 1$.

The combining ratio for alkali metals and oxygen is $2 : 1$.

#### Explanation:

Alkali metals form ${1}^{+}$ ions. Halogens form ${1}^{-}$ ions. Oxygen forms ${2}^{-}$ ions.

Ionic compounds are neutral, so the total positive charge has to equal the total negative charge.

Alkali metals plus halogens: potassium and chlorine

${\text{K"^+ + "Cl}}^{-}$$\rightarrow$$\text{KCl}$

The combining ratio for alkali metals and halogens is $1 : 1$.

Alkali metals plus oxygen: potassium and oxygen

${\text{2K"^+ + "O}}^{- 2}$$\rightarrow$$\text{K"_2"O}$

The combining ratio for alkali metals and oxygen is $2 : 1$.

Mar 10, 2017

Alkali metals all have a single valence electron, and halogens have a single missing one, so they would combine in a 1:1 ratio.

Oxygen requires two more valence electrons to complete its shell, so it would combine in a 2:1 ratio.

#### Explanation:

Elements combine (react) to form more stable compounds based on their electronic structure – specifically the valence electrons.

Groups 1, 2, and 17 (halogens) have only one more stable configuration, and Group 16 have a primary configuration, but may also have additional ones. The “transition metals” have a variety of possible stable electronic configurations with other elements. https://www.webelements.com/