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Ions and Isotopes Ions - Charged Atoms The identity of an element is determined by the number of in its nucleus. we change the o Therefore if we change the number of HOWEVER, If we change the number of electrons we do not change the element… instead, we have simply changed the overall charge Atoms can either loose of the atom. or gain electrons. Any time an atom becomes charged, we call it an ion . o If an atom gains electrons, it becomes a negatively charged ion. (anion) o If an atom loses electrons, it becomes a positively charged ion. (cation) Test Yourself! Complete the table below: Number of protons Number of electrons 10 10 0 ALUMINUM 13 10 3+ Y Al3+ Chlorine 17 18 1- y Cl- Nitrogen 7 9 2- y N2- Element Neon Net charge Ion? symbol (Y/N )n Ne How Many Electrons Gained or Lost? Atoms can become stable with a full valence shell of electrons. (last or outer orbit) Therefore, atoms will gain or lose the fewest number electrons possible to achieve a full valence o Metals tend to lose electrons to become positive ions (cations). o Non-metals tend to gain electrons to become negative ions (anions). Example: Magnesium (Mg) is a metal with 2 valence electrons To get a full outer shell it can either gain 6 electrons or lose 2 Therefore, it is more likely to lose electrons and form the cation Bohr Diagrams for Ions Bohr diagrams for ions have two modifications: 1. place square brackets around the whole diagram 2. write the charge in the top right corner, outside the brackets Practice: On a separate sheet of paper, try drawing the Bohr diagrams for K+, Be2+, N2-, and FNow try the H+ ion… neat eh? electrons. ion. example: Oxygen Ion (O2-) Isotopes – Changing the Atomic Mass Remember: There are 3 sub-atomic particles; protons, electrons and neutrons. Change the number of protons and you change the element Change the number of electrons and you create an ion Question: What happens when you change the number of neutrons? Sometimes atoms either gain or lose neutrons. Since neutrons have no charge this does not affect the charge of the atom. Neutrons have about the same mass as protons, so a change in the number of neutrons results in a change in the overall mass of the atom . Any time an atom has a different mass than is listed on the periodic table, we call it an isotope Example: . This means it has gained or lost neutrons 24 a) 12 26 b) 12 Mg Mg p =12 p = 12 e =12 e =12 n =12 n =14 . 12 M Magnesium a periodic These two atoms of Mg have the same number of electrons and protons , but a different number of neutrons . Which one is the isotope? Mg 24 . Practice – Use your periodic table to help complete the table below Name of Element Copper Oxygen Calcium Symbol Cu 29 62 Atomic Number 29 8 20 Relative Atomic Mass Number of Protons Number of Neutrons Number of Electrons Net Charge 63.5 29 33 28 +1 8 7 8 15 41 20 35 35 80 (Y/N) Isotope (Y/N) Y Y n Y Y Y Y n 0 21 Bromine Ion? 18 45 +2 -1 36