Question

Определите валентность атомов химических элементов по формулам вещества: NH4? H2S?SiH4?HBr?Ca3N2?CaCl2?Назовите 2 вещества,формулы которых записаны в задании последними

Answer 1

Валентности по порядку :
H - 1 (всегда) 
N - 4 
S - 2 
Si - 4 
Br - 1 
Ca - 2
N - 3
Ca - 2 
Cl - 1 
Валентность обозначается римскими цифрами !!!
Второе задание не понял , прости 

Answer 2

Valency of Chemical Elements

NH4: The formula NH4 represents the ammonium ion, which has a valency of +1. The ammonium ion is a positively charged polyatomic ion composed of one nitrogen atom and four hydrogen atoms. The nitrogen atom has a valency of -3, and the four hydrogen atoms each have a valency of +1, resulting in a total charge of +1 for the ion.

H2S: The formula H2S represents hydrogen sulfide. In this compound, hydrogen has a valency of +1, and sulfur has a valency of -2. Therefore, in hydrogen sulfide, two hydrogen atoms combine with one sulfur atom to form the compound.

SiH4: The formula SiH4 represents silane, which is a colorless, flammable gas with a strong repulsive odor. In silane, silicon has a valency of +4, and each hydrogen atom has a valency of +1. Therefore, in silane, four hydrogen atoms combine with one silicon atom to form the compound.

HBr: The formula HBr represents hydrogen bromide. In this compound, hydrogen has a valency of +1, and bromine has a valency of -1. Therefore, in hydrogen bromide, one hydrogen atom combines with one bromine atom to form the compound.

Ca3N2: The formula Ca3N2 represents calcium nitride. In this compound, calcium has a valency of +2, and nitrogen has a valency of -3. Therefore, three calcium atoms combine with two nitrogen atoms to form the compound.

CaCl2: The formula CaCl2 represents calcium chloride. In this compound, calcium has a valency of +2, and chlorine has a valency of -1. Therefore, one calcium atom combines with two chlorine atoms to form the compound.

The two compounds whose formulas are listed last in the question are Ca3N2 (calcium nitride) and CaCl2 (calcium chloride).

I hope this helps! If you have further questions, feel free to ask.