why does the reactivity of elements increase going down Group 1 from lithium to rubidium but decreases going down Group 7 from fluorine to iodine?

     The reactivity of group 7 elements decreases down the group because, as you go down the group: The atoms get larger. The outer shell gets further from the nucleus. The attraction between the nucleus and electrons gets weaker, so an electron is less easily gained.

Explanation:

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles

quartz

explanation: