The periodic law and periodic system
Answers are for parents and teachers.
1
Write the electron formula of potassium (Z = 19) and give its period and group.
1s²2s²2p⁶3s²3p⁶4s¹; period 4, main group I.
2
Why is calcium a stronger metal than magnesium?
Ca has more shells and a larger radius, so its two outer electrons are held more weakly and leave more easily.
3
How many protons, neutrons and electrons are in a ²⁷Al atom (Z = 13)?
13 protons, 14 neutrons (27 – 13), 13 electrons.
4
Chlorine or sulfur: which is more nonmetallic and why?
Chlorine; they are in the same period, and chlorine has a larger nuclear charge, a smaller radius and a stronger tendency to gain electrons.
5
Why do noble gases react with great difficulty?
Their outer shell is complete (ns²np⁶; two electrons in helium), so it is very stable.