fill in the missing words\na) there are valence electrons in an h₂co molecule.\nb) there are valence…

Explanation:

Step1: Determine valence - electrons of each atom

Hydrogen ($H$) has 1 valence electron, carbon ($C$) has 4 valence electrons, oxygen ($O$) has 6 valence electrons, sulfur ($S$) has 6 valence electrons, fluorine ($F$) has 7 valence electrons, nitrogen ($N$) has 5 valence electrons.

Step2: Calculate for $H_2CO$

For $H_2CO$, there are 2 $H$ atoms, 1 $C$ atom and 1 $O$ atom. So the number of valence electrons is $2\times1 + 4+6=12$.

Step3: Calculate for $SF_6$

For $SF_6$, there is 1 $S$ atom and 6 $F$ atoms. So the number of valence electrons is $6 + 6\times7=48$.

Step4: Calculate for $CN^-$

For $CN^-$, there is 1 $C$ atom and 1 $N$ atom. The negative charge means an extra electron. So the number of valence electrons is $4 + 5+1 = 10$.

Step5: Calculate for $NH_4^+$

For $NH_4^+$, there is 1 $N$ atom and 4 $H$ atoms. The positive charge means one less electron. So the number of valence electrons is $5+4\times1 - 1=8$.

Answer:

a) 12 b) 48 c) 10 d) 8