03 Electronic Configuration (Update).pdf
- 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 ions as 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 1 Nucleus Neutron 0 About 1 Nucleus 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 4 so 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 Covalent bonds are formed They form covalent molecules If electrons between elements are given and received Ionic bonds 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 2 3 4 Maximum number of electrons 2 8 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 Write down key ideas as you watch this video. 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 Called shells and 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 protons in the nucleus of each atom in a neutral atom
- 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” pattern i.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 drawn and 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 3rd 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 stabilises the 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 3rd 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 – 05 Drawing Bohr Diagrams (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 colour of the light. Thus, flame colours can be used to identify elements. This Photo by Unknown Author is licensed under CC BY-SA-NC
- 20. Flame Tests (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 Positive ions are known as CATIONS Negative ions 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 Hydrogen and Helium) 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 ion and that the chlorine atom becomes a chloride ion. (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.