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The Atom Atomic Number Mass Number Isotopes / Weighted averages Ions Read Chapter 4. Subatomic Particles. Particle Symbol Charge Relative Mass Electron e - -1 0 (negligible) Proton p + + 1 1 Neutron n 0 1. Atomic Number. Represents the number of
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The Atom Atomic Number Mass Number Isotopes / Weighted averages Ions Read Chapter 4
Subatomic Particles Particle Symbol Charge Relative Mass Electron e- -1 0 (negligible) Proton p+ + 1 1 Neutron n 0 1
Atomic Number Represents the number of protons in an atom- determines identity LecturePLUS Timberlake
Atomic Number on the Periodic Table 11 Na Atomic Number Symbol All atoms of an element have the same number of protons
Number of Electrons • An atom is neutral • The net charge is zero • Number of protons = Number of electrons • Atomic number = Number of electrons
Ions • An ionic particle’s number of electrons differs from the number protons • Results in a net charge. • More electrons than protons creates a negative charge (anion) • Less electrons than protons creates a positive charge (cation) • How many electrons are in the following particles? • Be+2 Br-1 Ga+4
Mass Number Represents the number of protons and neutrons in an atom LecturePLUS Timberlake
Atomic Symbols • Show the mass number and atomic number mass number 23 Nasodium-23 atomic number11 LecturePLUS Timberlake
More Atomic Symbols 16 31 65 O P Zn 8 15 30 LecturePLUS Timberlake
Isotopes • Atoms with the same number of protons, but different numbers of neutrons. • Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35Cl 37Cl 1717 chlorine - 35 chlorine - 37
Atomic Mass on the Periodic Table? • Look at the atomic mass for chlorine on the periodic table. How many neutrons do you think it has? • The average atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes. LecturePLUS Timberlake
Weighted Average Problems • The isotopes of chlorine are Cl-35 and Cl-37. In nature 76% of all Cl atoms have a mass of 35 amu (Cl-35) and 24% of all Cl atoms have a mass of 37 amu (Cl-37) LecturePLUS Timberlake
More Weighted Averages Notice that the average atomic mass of an element is close to the mass of the most abundant isotope. The average atomic mass of H is 1.00794 amu and it is calculated from H-1, H-2, and H-3. Which is the most common isotope? LecturePLUS Timberlake