reactivity series

• Which factor determines the reactivity of a metal?

  How easily the atoms of that element lose their outer electrons
• When metals react, do the atoms become positive or negative ions?

  they become positive because Metals lose electrons, and as electrons are negative, this will give them a positive charge. 
• The general word equation for the reaction between a metal and an acid is: Metal + Acid → Salt + Hydrogen
• Sodium reacts with water to produce sodium hydroxide and a gas.

  the gas is hydrogen because metal + water = salt and hydrogen