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Unformatted text preview: symbolized He has 2 electrons and two protons Carbon symbolized C has 6 electrons, 6 protons and 6 neutrons How the elements differ How the elements differ We arrange the elements in a table called The Periodic Table This Table Identifies each element by the number of protons and the mass From the number of protons and mass we can determine the number of neutrons More on Mass Later!! The modern periodic table. The Differences within Elements Differences Isotopes atoms of the same element with different Mass Why?? due to different number of neutrons E.g. Carbon 12 12C vs. Carbon 14 14C The Periodic Table gives the mass as the average of all isotopes present E.G. Carbon is listed as 12.01 Isotopes Isotopes
Mass number 12 C 13 C 14 C Atomic Symbols, Isotopes, Numbers
A Z X The Symbol of the Atom or Isotope X = Atomic symbol of the element A = mass number; A = Z + N Z = atomic number
(the number of protons in the nucleus) N = number of neutrons in the nucleus Isotope = atoms of an element with the same number of protons, but a different number of neutrons Ions – Charged Species Ions – Charged Species Atoms can gain or lose one or more electrons to produce charged species
23 Na 11
Loss of an electr on 23 Na 11 + + 1 el ectr on 35 Cl 17 + 1 el ectr on G ain of an electr on 35 Cl 17 - Atomic Masses Atomic Masses All isotopes have nearly identical chemical behavior The Mass of an atom is measured relative to the mass of an atomic standard The modern atomic mass standard is the carbon 12 atom C12 is defined as exactly 12 atomic mass units or amu’s Atomic Masses Atomic Masses Based on C12 defined as exactly 12 amu’s 1H has a mass of 1.008 amu’s The unit dalton (Da)...
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