20 11 23 Step 1: Sodium Na There are 11 protons + in one atom of sodium The smaller number isthe atomic number.It tells the number ofprotons in the atom( the atom's identity)Sodium11Na23There are 11 protons + in one atom of sodium
21 Na atomic # 11 23 p+ p+ p+ p+ p+ p+ p+ p+ p+ p+ p+ There are 11 protons + in the nucleus of a sodium atom
23 SodiumStep 2:11NaSubtract the number of protons + (11) from the number of particles in the nucleus (23)23 minus 11 =12 neutrons23The larger number is theatomic mass number. It tells the number ofprotons and neutrons together.There are 23 particles, or atomic mass units.11 protons + 12 neutrons = 23 amu’s total
27 Therefore, the number of Step 3:Most atoms areelectrically neutral.Therefore, the number ofelectrons can also bedetermined by theatomic number. Thereare usually the samenumber of electrons asthere are protons.Sodium11Na2311 electrons -11 protons usually means 11 electrons, too
28 Na e- atomic # 11 e- e- no no p+ p+ no no p+ no p+ p+ e- p+ e- no no LKe-e-11 electrons - total
29 atomic #11Na11 electrons - orbit in energy levels, or shells, around the densely packed nucleus of the sodium atom.
30 atomic #11NaBut there are specific numbers of electrons that can fit in each energy level of the atom.
31 Na Only 2 electrons - can fit in the first, or “K” shell atomic # 11 nonop+p+nonop+nop+p+p+nonop+noe-e-p+p+nonop+p+nonoK2 electrons - so far…. (9 more to go)
32 Na 8 electrons - can fit in the second, or “L” shell atomic # 11 e- e- nonop+p+nonop+nop+p+e-p+e-nonop+noe-e-p+p+e-nonop+p+e-nonoMLKe-e-10 electrons - so far……. ( added)… one more to go!
33 Electrons also fit in the valence, or outside shell, which in this case is the “M” shell. atomic #11Nae-e-nonop+p+nonop+nop+p+e-p+e-nonop+noe-e-p+p+e-nonop+p+e-nonoMLKWe only need to add one more electron for sodium, which fits easily in the “M” shell.e-e-11 electrons – total ( )