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Protons, Neutrons, Electrons We know that atoms are made of protons, electrons, and neutrons. The atomic number of an element is defined as the number of protons an atom of that element has in its nucleus. For a neutral atom, this will also be equal to the number of electrons the atom has. Ion and Isotope. Both have something the same, something different. Both start with the letter “i". Don’t confuse them! Isotopes are atoms of the same element that have identical numbers of protons but different numbers of neutrons. Ions are made when an atom gains or lose electrons. The mass number of an atom is the number of protons plus the number of neutrons in the atoms’s nucleus. The mass number is not found on the periodic table; it must be either given or be calculated. The mass number is used to identify the different isotopes of an element. For example, there are 2 different isotopes for Vanadium-50 and Vanadium-51. We can write this in different ways: Vanadium - 50 or 5023V or 50V 51 Vanadium - 51 or 51 V 23V or Here is a completely-written identification for an atom of Vanadium-51. Note the location of the mass number, the atomic number, and where the ion charge any) are written. You must remember what each of these numbers means, so that you can fully describe the isotope! Mass number 51 23 V Atomic number Ion charge (if none, it’s an atom, not an ion! • Protons: look it up on the periodic table to find its atomic number, which must equal the number of protons. • Neutrons: The number of neutrons is never written you must calculate it! Since mass # = protons + neutrons, and atomic # = protons. See above, 51-23 = 28 neutrons. • Electrons: The charge of the ion identifies the number of electrons compared to the number of protons. In a neutral atom, electrons = protons. When an atom loses electrons, it becomes positively charged (more protons than electrons). You may find this equation helpful: Charge = (number of protons) – (number of electrons) KEY THOUGHT: Unless you are shown it’s an ion you may assume that each line represents a neutral atom. Number of Protons Number of Neutrons Number of Electrons Isotope Symbol Atomic number Mass Number Isotope name 23 23 51 Vanadium-51 51 23 50 23 V a) 23 28 b) 23 27 23 23 50 Vanadium-50 c) 23 28 20 23 51 Vanadium-51 d) 47 62 47 47 109 Silver-109 109 Ag 47 e) 38 50 38 38 88 Strontium-88 88 Sr 38 48 62 46 48 110 Cadium-110 110 48 35 46 35 35 81 Bromine-81 81 Br 35 35 44 36 35 79 Bromine-79 79 Br 35 i) 22 24 18 22 46 Titanium-46 46 Ti+4 22 j) 88 135 88 88 223 Radium-223 223 Ra 88 V +3 f) g) h) 51 23 V Cd +2 1- 182 W2+ k) 74 108 72 74 182 Tungsten-182 74 8 8 8 8 16 Oxygen- 16 16 O 8 m) 8 9 8 8 17 Oxygen- 17 17 O 8 18 O 8 l) n) 8 10 8 8 18 Oxygen-18 p) 53 74 54 53 127 Iodide - 127 127 –1 I