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4.3 Distinguishing Among Atoms. Elemental Identities. Elements are different because they contain different numbers of protons (110) Atomic number – Number of protons in the nucleus of an atom (110) Oxygen is the eigthth atom on the periodic table and has 8 protons
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Elemental Identities • Elements are different because they contain different numbers of protons (110) • Atomic number – Number of protons in the nucleus of an atom (110) • Oxygen is the eigthth atom on the periodic table and has 8 protons • Sodium is the 11th atom and has 11 protons
Other Subatomic particles • Atoms are Neutral • Number of protons equals the number of protons • Neutrons – the number of neutrons in an element can vary. The various combinations are called Isotopes
Isotopes Mass number Number of protons + number of neutrons Oxygen has an average atomic mass of approximately 16 amu 8 protons + x neutrons= 16 amu
Isotopes • Periodic table lists the average atomic mass of each element according to their natural abundances. • Lets examine one of the elements and their relative natural abundances
Carbon • Carbon has two noteworthy isotopes • Carbon 12 • 6 protons and 6 neutrons • Atomic mass = 12 amu • Carbon 13 • 6 protons and 7 neutrons • Atomic mass = 13 amu
Carbon • Reported atomic mass = 12.01 amu • Isotopic masses • Carbon 12 = 98.89% • Carbon 13 = 1.11%
Chlorine • Two isotopes • Chlorine 35 = 75.77% • Chlorine 37 = 24.23% • Reported atomic mass =
Building atomic nucleus • Determining the number of protons and average number of neutrons in an element (rounded to whole numbers)