03 Electronic Configuration (Update).pdf

Chemistry

1. Year 8 Science -Chemistry
03 Electronic Configuration

2. Learning Objectives
Explain what electronic configuration is.
Write the electronic configuration for the first twenty elements.
Draw the electronic configuration for the first twenty elements.
Define ionsas an atom or group of atoms that carries a positive
or negative electric charge because of having lost or gained one
or more electrons.

3. RECAP
-Atoms contain smaller particles (Subatomic particles)
Protons
Positive charge (+)
Neutrons
Neutral (no charge)
Electrons
Negative charge (-)

4. RECAP -Differences between subatomic particles
Name of
subatomic
Particle
Charge Mass
Location in
atom
Proton +1 About 1Nucleus
Neutron 0 About 1Nucleus
Electron -1 Close to 0
Orbiting
nucleus
•Protons and
neutrons are
almost equal
in their
masses.
•Electrons are
almost
massless.

5. RECAP -Atomic Structure
In our most basic atomic model, each subatomic particle has a
unique home:
Electrons orbit the nucleus in shells
The outermost shell is called the
valence shell
Neutrons and Protons are found in the
central component called the Nucleus

6. RECAP
The Periodic Table -Organisation
Horizontal Rows = Periods
Numbered 1 to 7
The period number for an element tells you how many electron shells
it has in its atoms.
E.g.Calcium is in Period 4so it has 4 electron shells.
Vertical columns = Groups
Numbered 1 to 18
Same number of outermost shell electrons (valence electrons), hence
similar chemical properties

7. Elements can bond together
-Electrons are involved
If electrons between elements are shared
Covalentbonds are formed
They form covalent molecules
If electrons between elements are given and received
Ionicbonds are formed
They form ionic crystals(in solid form)
Write notes!
We will revisit these ideas towards the end of the unit.

8. Drawing Electron Shells
Niels Bohr used experiments to determine that not all the electrons were found in the
same spot.
Instead, each electron was found in a unique “shell” / energy level
These “shells” orbit the nucleus because the negative charge on the electron is attracted to the
positive charge on the Nucleus.
Bohr also developed rules to show how many electrons could be in each shell.

9. Drawing Electron Shells
-Remember this slide?
Drawing an accurate picture of an atom
using a diagram is difficult because
electrons cannot be observed like most
particles.
Their exact location within the atom is
never known —they tend to behave like a
‘cloud’ of negative charge.

10. Drawing Electron Shells
Shell number
(from the nucleus
outwards)
1 234
Maximum
number of
electrons
28
8
(18)
2
(32)
•You will only be required to draw shell diagrams for the first 20 elements of the periodic table (up to Calcium)
•Shells 3 and 4 can actually hold more electrons (numbers in brackets) due to a concept known as “subshells”
(VCE Chemistry!!!) – you only need to remember 8 and 2 for now.
Write notes!

11. Electron Shell Diagrams-https://youtu.be/hSkJzE2Vz_w
Writedown keyideasasyouwatchthisvideo.
Write notes!

12. Electron Shell Diagrams
Simplified model of an atom
Nucleus of the atom is drawn in the middle
Electrons arranged in a series of energy levels around
the nucleus
Calledshellsand are drawn as concentric rings around
the nucleus.
Electrons in the inner shells are more strongly
attracted to the nucleus than those in the outer
shells
Electron configuration is determined from the atomic
number of the element, which is the same as the
number of protonsin the nucleus of each atom in
aneutralatom

13. Steps to follow when drawing electron shell diagrams
Write out the number of protons and neutrons in the nucleus by using both the
atomic and mass numbers on the periodic table.
e.g.2p 2n for Helium (write them one on top of the other)
Find out which period the element is in–the period number tells you the
number of shells it has
Draw the shells as concentric circles
Find out the total number of electrons(same as the atomic number for a
neutral atom)
Fill up the electrons in the shells, starting with the first shell
Always fill electrons up in a “cross” patterni.e.up, down, left, right
Once you reach the maximum number of electrons in one shell, start adding electrons
to the next shell
Count the total number of electrons you have drawnand make sure it matches
the atomic number
Refer to this slide when you are doing the worksheet “05 – Drawing Bohr Diagrams”.

14. Steps to follow when drawing electron shell diagrams

15. Extension –Why do we not go up to 18
electrons immediately in the 3
rd
shell?
The third shell can hold up to 18 electrons but there are
only eight elements in the third period. This is because the
outer shell of an atom can never hold more than eight
electrons as the atom would then become unstable.
While the third shell is yet to be filled completely,
electrons begin to fill the fourth shell in both potassium
and calcium atoms. This stabilisesthe atoms because the
third shell is no longer the outer shell.
The filling of the third shell resumes in the block of
elements from scandium to zinc (the transition metals).
Once the third shell is full, the fourth shell continues to fill
from gallium to xenon.
Electronic configuration for
Potassium is 2,8,8,1

16. Extension –
Why do we not
go up to 18
electrons
immediately in
the 3
rd
shell?
Calcium as an
example

17. Extension: Electron Sub-Shell Configuration
Read and follow:
https://chemistry.stackexchange.com/quest
ions/31189/what-is-spdf-
configuration#:~:text=These%20subshells
%20are%20called%20as,so%20its%20called
%20as%201s.
Using the Aufbau Principle, write the sub-
shell notation for the first 10 elements
https://youtu.be/UDmrRWeFWwU

18. You do:
Worksheet–05DrawingBohrDiagrams
(You will need your Periodic Table)

19. Flame Tests
(Teacher Demo)
If enough energy is supplied to an atom, electrons can
move from one shell (or energy level) to another
(higher) energy level.
This may occur when atoms are heated by a flame.
When electrons move between energy levels, they either
absorb or emit an amount of energy related to the
difference in energy between the energy levels.
Electrons returning to a lower energy level emit this
energy in the form of light.
The size of the difference in energy levels
determines the colourof the light.
Thus, flame colourscan be used to identify
elements.
This Photo by Unknown Author is licensed under CC BY-SA-NC

20. FlameTests (Teacher Demo)
Different elements have different electronic configurations
•Therefore, their electrons will have their own unique way
of moving up and down energy levels.

21. You do:
Practical–03 Flame Test Teacher Demo Practical Worksheet
Focus on how we write:
Hypothesis
Method
Results and Observations
Conclusion

22. Ions-https://youtu.be/900dXBWgx3Y
Write down key ideas as you watch this video.
Write notes!

23. Ions have more or less electrons
Group 1, 2, 3 elements (metals)
Tend to lose electrons
Gain positive charge of +1, +2, +3
Group 15, 16, 17 elements (non-metals)
Tend to gain electrons
Gain negative charge of -3, -2, -1
When the
elements gain
or lose
electrons, they
are known as
IONS
Write notes!

24. Special names for ions
Positiveions are known as
CATIONS
Negativeions are known as
ANIONS
Remember the names as “Cats and Ants”
Write notes!

25. The Octet (or Duplet) Rule
The tendency of atoms to prefer to have 8 (or 2, in the case of HydrogenandHelium)
electrons in the valence shell.
Atoms with less than 8 (or 2) electrons tend to react to form more stable compounds.
1.Would Magnesium be stable
in this state?
2.What does it need to do to
adhere to the octet rule?
Write notes!

26. What do you notice about the outer shell of the two
ions?
The outermost electron shell (also known as the valence shell) is completely filled!
This is the most stable arrangement of electrons.
Their electronic configuration looks like that of a Noble gas (Group 18).
Write notes!
Note that the sodium atom becomes a sodium ionand that the chlorine atom becomes a
chlorideion. (When non-metals form ions, a suffix is added, in this case “ide”.)

27. How do we know when elements gain or lose
electrons?
We look at the number
of valence electrons
they have.
Write notes!

28. How do we know an ion’s eventual charge?
Determine whether it is easier to
lose or gain electrons.
E.g.for Sodium (Group 1), it is
easier to lose 1 than to gain 7.
Find the difference between the
final number of protons (positive
charge) and electrons (negative
charge).
E.g.for Sodium, it will have 10
electrons but 11 protons –one
extra positive charge!
Write notes!

30. You do:
Worksheet–06 Ion Formation Practice
(You will need your Periodic Table)

31. Reference
Answers for “06
Ion Formation
Practice”
Worksheet

32. You do:
SQ10 Chapter 4.3
Textbook Questions 1 to 5
Remember to use the studying technique that suits you best:
Think about your answer, then look at the model answer and write this directly into your notebook OR
Write your own answer, then amend it using the model answer.