Atomic Structure & Periodic Table Atoms introduction Electronic structure brings you back here. end THE PARTICLES IN THE ATOM Number of protons and Small central electrons nucleuswill always be equal the of an in aninatom nucleus element. So overall, they have no In shells around electrical the atom charge. mass charge proton 1 +1 neutron 1 0 electron -1 Atoms of different elements have different numbers of protons proton number Any atomThe with Nitrogen proton 6 protons atoms number in have the of nucleus neon 7 protons is 10. must be carbon. The mass The proton number is sometimes called the atomic number is the total number. number of It is the number of protons present in neutrons in an atom. the nucleus of an atom. mass number (protons + neutrons) Proton number 14 6 C protons & So this atom of carbon has : 6 protons (14 – 6) = 8 neutrons. 6 electrons to make the atom electrically neutral ISOTOPES. These are atoms of the same element with different numbers of neutrons Chlorine has two different isotopes 35 17 Cl 37 17 Cl 17 protons 17 electrons (35 – 17) = 18 neutrons 17 protons 17 electrons (37 – 17) = 20 neutrons same number of protons same element. different numbers of neutrons ELECTRONS occupy particular energy levels (“shells”) around the nucleus of the atom. The electrons in an atom will always occupy the lowest available energy levels. The innermost shells closest to the nucleus will fill up first, as atoms contain more electrons. If an atom has more than 10 electrons, electrons start to fill the third shell out. 2 max 8 max 8 max the second shell can contain eight electrons, Once the third maximum. shell has eight electrons, the fourth shell starts If an atom has more to fillthan 2 electrons, electrons start to fill this next shell out. So more than 18 electrons in the the atom, lowest means energy thelevel fourth can shell begins contain to only be occupied two electrons. by electrons. shell full x xx 16 8 x O xx x The In the electronic shells :structure 8 electrons is 2(x) :6 x shell full shell full x shell full x x x x x x x x xx x x x x x x In the nucleus : 8 protons 8 neutrons xx 39 19 K In the nucleus : 19 protons 20 neutrons In the shells : 19 electrons The electronic structure is 2 : 8 : (x) 8:1 THE PERIODIC TABLE. Group Group 7 0 The elements in this table are the “building NON-METALS blocks” of all materialsGroup Group Group Group Group Group METALS H He 3 4 5 6 1 2 Li Be Na Mg K Ca Elements in this central block are known as TRANSITION METALS. Cr Fe C N O Al Ne Cl Ar Ni Cu Zn The 100 chemical elements can be arranged in order of their increasing atomic numbers in horizontal rows. -- watch appear in order of increasing of This listthem is arranged so that elementsnumbers with similar chemical protons in the nuclei of their properties come in atoms. vertical columns together. These are GROUPS. Properties are similar but there is a gradual change in the properties of a group as you go from the top to the bottom PERIODIC TABLE WITH THE FIRST 20 ELEMENTS. 1 H 1 3 THE ATOMIC (PROTON) NUMBER IS ABOVE EACH SYMBOL 2 THE ELECTRONIC STRUCTURE IS BELOW EACH SYMBOL 2 4 5 6 7 8 9 10 He Li Be B C N O F Ne 2:1 11 2:2 12 2:3 13 2:4 14 2:5 15 2:6 16 2:7 17 2 :8 18 Na Mg Al Si P S Cl Ar 2:8:1 2:8:3 2:8:4 2:8:5 2:8:6 2:8:7 2:8:8 2:8:2 19 20 K Ca 2:8:8:1 2:8:8:2 The The halogens in group 71 allall have seven electrons in their metals The noble in group gases in have group one 0third all electron have inlevel Here, across the second period, the second Here, across the third period, the energy outermost shells. The other two halogens that come full their outermost electron shells shells. energy level is outer gradually filling with electrons is gradually filling with electrons below fluorine & chlorine are bromine anddon’t iodine. This gives them stability & explains why they react.