1. How Are Electrons Arranged?
Electrons are not evenly spread.
The exist in layers known as shells.
The arrangement of electrons in these shells is often called the electron configuration.
1st Shell
2nd Shell
3rd Shell
4th Shell

2. How Many Electrons per Shell?
Each shell has a maximum number of electrons that it can hold.
The maximum
1st Shell: 2 electrons
2nd Shell: 8 electrons
3rd Shell: 18 electrons

3. Which Shells Do Electrons go into?
Opposites attract.
Protons are + and electrons are – charged.
Electrons will occupy the shells nearest the nucleus unless these shells are already full.
1st Shell: Fills this first
2nd Shell: Fill this next
3rd Shell: And so on

4. Working Out Electron Arrangements
How many electrons do the element atoms have? (This will equal the atomic number).
Keeping track of the total used, feed them into the shells working outwards until you have used them all up.
Drawing neat diagrams helps you keep track!
1st Shell: Fills this first
2nd Shell: Fill this next

5. Electron Arrangements
A drag and drop activity

6. Key Points
Shells are labelled by giving each a principle quantum number, n. For the first shell n = 1, for the second shell n = 2…
The number of electrons in the outer shell determines the group number.
The quantum number of the shell determines the period to which an element belongs.

7. Which of the following is not a subatomic particle?
Proton.
Isotope.
Neutron.
Electron.

8. The element Cobalt has a relative atomic mass of 59 and an atomic number of 27. Which of these is a true statement about each neutral cobalt atom?
It contains 59 neutrons.
It contains 27 electrons.
It contains 32 protons.
It contains equal numbers of neutrons and electrons.

9. contains more protons than neutrons.
The Periodic Table displays iron as shown below. This indicates that Fe atoms:
contain 56 neutrons.
contain 30 electrons.
contain 26 protons.
contains more protons than neutrons. 56 Fe 26

10. Which of the following is true: Both isotopes contain 35 protons.
Bromine consists of a mixture of two isotopes: Bromine-79 and Bromine-81
Which of the following is true:
Both isotopes contain 35 protons.
Bromine 79 contains 46 neutrons.
Bromine 81 contains 44 neutrons.
Bromine-81 is more reactive than bromine-79. 80 Br 35

11. Natural boron consists of approx. 20% boron-10 and 80% boron-11.
What will the relative atomic mass of natural boron will be?
10.0
11.0
10.5
10.8 ? B 5

12. Which answer best describes the shell arrangement of the electrons in a sodium atom?
2,8,1.
2,2,7.
2,8,8,3.
2,8,8,1. 23 Na 11

13. Which answer best describes the shell arrangement of the electrons in an oxygen atom?
2,8,6.
2,8,8.
2,8.
2,6. 16 O 8

14. Which of these elements will have electron shells that are either full or empty (i.e. not partially full)? 14 N 7 A 40 Ar 18 B 40 Ca 20 C 27 Al 13 D

15. Which answer best describes the shell arrangement of the electrons in an oxide ion O2-?
2,8,6.
2,8,8.
2,8.
2,6. 16 O 8