There is a whole video describing the grammar but its in Japanese .
How would you explain the difference between:
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The expression になる is mainly used to express a "natural" change, while the となる expression is used to express a change to a final stage.
First example: 彼がリーダーになった: He became a leader (naturally). 彼がリーダーとなった: He became a leader (he finally made it, maybe struggling, maybe he had to face a lot of challenges, etc.).
Second example: 夜になったら、雨が雪になった: When the night came, rain turned into snow (If I am in a snowy area, this is naturally expected). 夜になったら、雨が雪となった: When the night came, rain turned into snow (If I am NOT in a snowy area, this might not expected).
Hope it helps.