AD n°6 sur la santé - Les sciences à La Salle

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1G(*2%&'!1&!.&*!+9+%&)*H!I99&!'G&JK4/%&!&)!L4(%%&!K(4!%29&!?LH%29M<EH!!
Les!valeurs!des!masses!molaires!atomiques!des!éléments!figurent!dans!la!classification!
périodique!des!éléments.!!
Pour!calculer!la!masse!molaire!atomique!d'un!élément,!il!faut!prendre!en!compte!
l'ensemble!de!ses!isotopes.!Les!proportions!d'isotopes!sont!celles!que!l'on!rencontre!
dans!la!nature.!!
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Elle!est!égale!à!la!'2%%&!des!%(''&'!%29(/4&'!(*2%/>3&'!de!tous!les!atomes!présents!
dans!la!molécule.!!
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Détailler!avec!précision!votre!raisonnement.!
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