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• Proton = + charge • Neutron = neutral charge • Electron = - charge Ions • Ions are atoms that have lost or gained one or more electrons giving them a positive or negative charge! If an ion gains an electron it has a negative charge. If an ion looses an election it has a positive charge. For example: Na (Sodium), has originally 11 electrons but when an electron is lost it becomes a postive ion. Na + What causes an atom to become an ion? • When an atom loses or gains one or more electrons it acquires a net electrical charge called an ion. • The net charge of an ion is found by subtracting the number of electrons from the number of protons Charge of Ion = number of protons – number of electrons A neutral magnesium atom (atomic number=12) has 12 protons/electrons. If it loses 2 electrons it becomes an ion with a charge of 2+. Number of protons 12 Number of electrons - 10 Charge of Ion 2+ Ion 19. Cu²+ 20. F- Protons Electrons 29 27 9 10 Isotopes • Isotopes are atoms that have the same number of protons but different numbers of neutrons • Most elements in the first two rows of the periodic table have at least 2 isotopes with one being more common than the other • In nature, elements are almost always found as a mixture of isotopes Hmm Isotopes of Hydrogen •For example, the most common isotope of hydrogen has no neutrons at all •There's also a hydrogen isotope called deuterium, with one neutron, and another, tritium, with two neutrons. Most common isotope Neutron Proton Hydrogen Deuterium Tritium • To identify an isotope more specifically, chemists add a number after the elements name. ex. Carbon-11 Carbon-12 Carbon-14 • This number is called the isotope’s mass number and is the sum of the isotope’s number of protons and neutrons. • For example, an atom with 17 protons and 20 neutrons has a mass number of 37. Q. What is the mass of the Nitrogen isotope with 7 protons and 12 neutrons? A. Nitrogen-19 Examples Atom iodine-128 potassium-40 Protons 53 Neutrons 75 Electrons 53 19 21 19 To name an isotope using chemical symbols simply place the atom’s mass number to the upper left of the element symbol. For example 37Cl. #neutrons = atomic mass – atomic number 37 – 17 = 20 neutrons How many protons, neutrons, and electrons are present? 56 26Fe 2+ STEP 1: The atomic number in the lower left corner = 26 protons. The difference between the mass number and the atomic number is 56 – 26 = 30. There are 30 neutrons. STEP 2: The charge on the ion, 2+ shows us that there are 2 more protons than electrons, indicating that there are 24 electrons. Isotope Symbols Mass number (M) 141 Ba 56 Atomic number (Z) 2+ Charge Number of protons = Z Number of neutrons = M – Z charge = Z– Number of electrons