For a mineral . `liAl (SiO_3)_2`, what is the charge on `SiO_3` unit ? What is the arrangement fo oxugen atoms around the silicon atom ?

Explanation

Positive charge on ` Li` group `1` elecment `= + 1`
Positive charge on `Al`, group ` 13` element `= + 3`
Total psitive charge on cations `underline ulbar(= +4)`
Since `Al (SiO_3)` units should by `-4` or each `SiO_3` unit must carry two units of negative charge and should be repessented as `(SiO_3)^(2-)` . From this formula . it appears there are only three ocygen atoms per silicon atom, But actually all silicates consiste of `SiO_4^(-4)` unit . Therefore, in the given silicate, two of the oxygen atom per silicate unit are shared bewteen two silicate group , thus giving rise to linear chain silicate .
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