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In an atom, the electrons are arranged in shells around the nucleus. The electrons fill the shells from the nearest shell to the nucleus, outwards. Electron shells can only hold limited numbers of electrons. 21/11/2018 nrt

Electron Orbitals The first shell can hold 2 electrons 2 The second shell can hold 8 electrons 2,8 The third shell can hold up to 18 electrons 2,8,18 21/11/2018 nrt

Li Be B C N O F Ne Na Mg Al Si P S Cl Ar If we examine the elements in the two short periods of the periodic table we can see a pattern in their atomic number... Li 3 Be 4 B 5 C 6 N 7 O 8 F 9 Ne 10 11 Na 12 Mg 13 Al 14 Si 15 P 16 S Cl 17 18 Ar The number of electrons in an atom is the same as the atomic number of the element. 21/11/2018 nrt

1st Short Period - Electronic Structure The numbers below each atom are the electron configurations of the atoms, e.g. the electron configuration of a Carbon atom is 2,4. This means that a Carbon atom has two electrons in the first shell and four electrons in the second shell. Remember: The atomic number is the same as the number of electrons. 21/11/2018 nrt

2nd Short Period - Electronic Structure The electron configuration of a Sulphur atom is 2,8,6. This means that a Sulphur atom has two electrons in the first shell... ...eight electrons in the second shell... ...and six in the third. Remember: The atomic number is the same as the number of electrons. 21/11/2018 nrt

The electron shells fill as we move across and down the periodic table. 21/11/2018 nrt

The 2nd short period shows the pattern in electronic structure of atoms as you move across the table and helps to show how the structure affects the physical and chemical properties of the elements. At the left hand end of the period the atoms have only a few electrons in their outer shell. At the right hand end of the period the atoms have almost full or full outer shells of electrons. 21/11/2018 nrt

The elements change gradually in nature as we cross the period from left to right. The elements on the left are metallic elements, and the elements to the right are non-metallic. The electronic structures dictate that elements with a few electrons in their outer shells can most easily lose electrons to form positive ions... ...and that elements with a few spaces in their outer shells can most easily gain electrons to form negative ions. 21/11/2018 nrt

Sodium is a reactive metal Argon is an unreactive gas 21/11/2018 nrt

Group 1 - Electronic Structure Li 3 In group 1 the essential nature of all the elements is identical, but the presence of an increasing number of full shells inside the outer shell does affect the properties. As we descend the group, the metals become more reactive. Lithium reacts with cold water on contact and slowly dissolves to form a solution of Lithium hydroxide. Caesium reacts explosively on contact with cold water to form a solution of Caesium hydroxide. 2,1 In group 1 of the periodic table we can see that all of the elements have one electron in their outer shell. This similarity in electron structure explains the fact that the elements in group 1 have similar chemical properties. In most of their chemical reactions, the atoms release this electron and become positively charged ions. Na 11 2,8,1 K 19 2,8,8,1 Rb 37 2,8,18,8,1 Cs 55 2,8,18,18,8,1 21/11/2018 nrt

Group 7 - Electronic Structure In group 7 the essential nature of all the elements, the Halogens, is identical, but the presence of an increasing number of full shells inside the outer shell does affect the properties. The elements all form diatomic molecules, e.g. F2, Cl2. As we descend the group, the Halogens become less reactive. In group 7 of the periodic table we can see that all of the elements have an outer shell with one empty space. This similarity in electron structure explains the fact that the elements in group 7 have similar chemical properties. They are non-metallic coloured elements with many similar chemical properties. F 9 2,7 Cl 17 2,8,7 Br 35 2,8,18,7 I 53 2,8,18,18,7 21/11/2018 nrt

The elements in group seven all form diatomic molecules, e.g. F2, Cl2. They are all colourful non-metals. 21/11/2018 nrt

Group 0 - Electronic Structure In group 0 of the periodic table we can see that all of the elements have full outer shells of electrons. This similarity in electron structure explains the fact that the elements in group 0 have similar chemical properties. The elements are very stable and unreactive. They are found most commonly in nature as single atoms. In group 0 the essential nature of all the elements is identical, but the presence of an increasing number of full shells inside the outer shell does affect the properties. As we descend the group the gases become heavier and ‘more’ reactive. Helium and Xenon have no known natural compounds. However, Xenon can be induced to react with Fluorine under extreme conditions. He 2 2 Ne 10 2,8 Ar 18 2,8,8 Kr 36 2,8,18,8 Xe 54 2,8,18,18,8 21/11/2018 nrt

A Space Filling Model of Xenon Tetrafluoride 21/11/2018 nrt

If the electrons in an atom were particles! ...and if we could freeze the atom at a moment in time! ...and if we had a microscope that could see the atom! ...is this what a lithium atom would look like? 21/11/2018 nrt

OR ... If the electrons in an atom were particles! …and in very rapid motion around the nucleus, so rapid that they appear as a blur... ...is this what a Xenon atom would look like? What do you think? 21/11/2018 nrt