In centre of atoms there is nucleus and in nucleus,there are protons(positively charged) and neutrons(neutral).mass of protons are 1.00782 amu and mass of neutrons are 1.00836 amu.Due to positivity of protons,it is positively charged.

Yes,ionic compound is formed

When water is heated,it contracts up to 4degree Celsius,so it's density increases and above 4degree Celsius,it expands,so it's density decreases. When hot water is cooled,it contracts up to 4degree Celsius and below 4degree Celsius it expands.So,water has maximum density at 4degree Celsius and it's density decreases below and above density at 4degree.