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Access to Science: Chemistry

Access to Science: Chemistry

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Access to Science: Chemistry

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  1. Have a go at the element word search, use your periodic tables to help you! Access to Science: Chemistry Week 2 electronic configuration, basic and advanced. Are you ready to learn? Lab notebook out and a pen No food out, drinks away Phones on silent and in your bag Bags and coats under bench or at the back.

  2. An atom is the basic unit of matter, the stuff all around us. • A substance that contains only one sort of atoms is called an element. • Atoms contain 3 fundamental particles: protons and neutrons in the nucleus and electrons orbiting the nucleus. • The proton is positively charged • The neutron is neutral • The electron is negatively charged. • Only the protons and neutrons have significant mass and are responsible for the physical properties of an element. • The electrons are responsible for the chemical properties. Recap...

  3. There are about 100 naturally occurring elements, these are pure substances. • All atoms of a particular element contain the same number of protons and electrons. This number is called the Atomic number for that element and is found on the periodic table. • We can work out the Mass number by adding together the number of protons and neutrons in a given atom of an element.. • To give a more precise mass number, we work out the isotopic abundance, an average of the percentage of atoms with different mass numbers of that element. • This number is called the Relative Atomic Mass. • We can find the Relative Atomic Mass (Ar) of an element by using a machine called a mass spectrometer. What do we remember? News!

  4. Rationale for this session: Elements, compounds and mixtures, end on combining power of the elements to form compounds. Atomic structure – Bohr’s model Go onto A’level material – expand Bohr model to the quantum mechanical model Stop and Go signs, to help me know you understand

  5. Recall electronic structure – Bohr model • Expand knowledge of electronic structure to spdf configuration Learning aims for the session

  6. Theorised that electrons existed at quantized energy levels, not just whizzing around the nucleus. Neils Bohr’s atomic model

  7. Atoms arranged with protons and neutrons in the small nucleus at the centre of the atom • Electrons arranged in numbered shells or they can be thought of as a set (quantised) energy levels. • Still orbiting the nucleus like the planetary solar system, but at set distance of certain energy. • Lowest energy level nearest the nucleus, electrons like existing in regions of lowest energy. • 1st energy level containing maximum 2 electrons • 2nd energy level containing maximum 8 electrons • 3rd energy level containing 8 electrons Activity P6 ee Electronic structure e e B: 5 p+ 6n0 e e.g. boron: 5 protons, 6 neutrons and 5 electrons e e e

  8. When we want to write this out instead of drawing it, we can use short notation: For example : neon Atomic number 10, so 10 protons and 10 electrons in the neutral atoms. We begin by filling the innermost shell with 2 electrons, this has the lowest energy level. This leaves 8 remaining electrons, which go into the next shell, this has the next lowest energy level. We can write this in short notation as Ne 2,8 Activity P 7 Electrons in shells / energy levels

  9. Neils Bohr theorised: • Energy levels (shells) were present in an atom. • Atom likened to a solar system of orbiting electrons in these defined shells • Each shell/ level had set energy • BUT ......this model worked for only hydrogen, but there were inconsistencies when looking at other elements. • He found not all the electrons within a shell had the same amount of energy as thought, but they still had definite amounts of energy. It’s about to get complicated!

  10. It took the work of Heisenberg and Schrödinger to come up with ways of describing more fully the precise energy levels of electrons within atoms. • This gave rise to the particle-wave model. • Their findings were based on mathematical formulations and predicted that there was an uncertainty about where electrons were actually found and their model helped to state the most likely place to find electrons. • What they said was: Bohr’s energy levels had distinct areas within them – sub-shells or sub-levels. • Think of it as an electrons address: the street is the energy level, the house is the sub-level. Quantum theory – wave-particle model

  11. In the innermost (lowest energy) shell - 1 sub-shell named s which could hold only 2 electrons, as before. • In the next shell, shell 2, we can have 2 sub levels of differing energy called s and p. • S will hold 2 electrons and p, 6 electrons • In the third shell, there are 3 sub levels of differing energy call s, p and d. • S again only holds 2 electrons, p, 6 electrons and d will hold 10 electrons. (note the change from Bohr’s model.) • In the fourth shell there are 4 sub-levels: s, p, d, f • These hold 2 electrons in s, 6 electrons in p, 10 electrons in d and 14 electrons in f. • Have a go at filling up the table on page 8 Sub-shell (orbitals) summary...

  12. activity Worksheet P8

  13. activity f d p d s p s p s s The s level always fills before the p level The 4s level always fills before the 3 d level as this has a bit lower energy The same happens with 5s and 4d etc. Rising energy - increasing distance from the nucleus Showing the electrons in terms of their energy... n = 1 2 3 4 Energy levels (s, p, d and f)

  14. Our sub-shells: 1s, hold 2 electrons • 2s 2p holds a total of 8 • 3s 3p holds a total of 8 • 4s 3d 4p holds a total of 18 • For H = 1e where’s it going to go Don’t forget 2 electrons in s, 6 in p, 10 in d and 14 in f Activity on P9 : first find out the atomic number to tell you how many electrons the atom has, then begin adding them to each sub-level, writing them as 1s22s22p6 etc.

  15. Here’s the periodic table, it’s arranged in order of increasing atomic number, which means each element from left to right has another electron in its outer shell. Think of the period numbers down the side as the shells numbers. How many sub shells in the lowest energy shell, the one nearest the nucleus? What we end up with is....

  16. We have looked at how the electrons are arranged and how it is the electrons that give an element it’s chemical properties.... Electrons and chemical change.

  17. Elements and compounds are pure substances. • A compound is something pure that is formed from a chemical reaction with more than one element. The elements are chemically bonded together. • Let’s look! Elements, compound and mixtures.

  18. 1st practical: elements, compounds and mixtures!

  19. Recall electronic structure – Bohr model • Expand knowledge of electronic structure to spdf configuration Learning outcomes

  20. Review the powerpoint on the website • • Build an A3 sized poster in your lab notebook, containing all the items on the sheet, this will help when you come to write up your assignments. Homework