Answer:
Two electrons fit in the first shell out from the nucleus and eight fit in the second. Every element with more protons than the two of Helium needs to work on shells outside the first one. one you get to ten, you have filled the first two shells.
In a water molecule, oxygen forms one covalent bond with EACH of TWO hydrogen atoms. As a result, the oxygen atom has a stable arrangement of 8 valence electrons. Each hydrogen atom forms only one bond because it needs only two electrons to be stable.
 
        
             
        
        
        
Answer:
207g
Explanation:
Given compound: 
             Ca(ClO₃)₂
The equivalent mass can be derived by summing the molar masses of each atom
   Molar mass of Ca = 40
                             Cl  = 35.5 
                             O  = 16 
 Now solve; 
  Molar mass  = 40 + 2(35.5 + 3(16)) = 207g
 
        
             
        
        
        
Answer:
 1.73 atm
Explanation:
Given data:
Initial volume of helium = 5.00 L
Final volume of helium = 12.0 L
Final pressure = 0.720 atm
Initial pressure = ?
Solution:
"The volume of given amount of gas is inversely proportional to its pressure by keeping the temperature and number of moles constant"
Mathematical expression:
P₁V₁ = P₂V₂
P₁ = Initial pressure
V₁ = initial volume
P₂ = final pressure
V₂ = final volume  
Now we will put the values in formula,
P₁V₁ = P₂V₂
P₁ × 5.00 L = 0.720 atm × 12.0 L
P₁ = 8.64 atm. L/5 L
P₁ = 1.73 atm
 
        
             
        
        
        
It is called rust and it forms when water soaks into the metal forming a chemical reaction.