The atom and Isotopes.

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Presentation transcript:

The atom and Isotopes

# protons in an atom = # electrons Atomic Number Atoms are composed of identical protons, neutrons, and electrons How then are atoms of one element different from another element? Elements are different because they contain different numbers of PROTONS The “atomic number” of an element is the number of protons in the nucleus # protons in an atom = # electrons

Atomic Number Atomic number (Z) of an element is the number of protons in the nucleus of each atom of that element. Element # of protons Atomic # (Z) Carbon 6 Phosphorus 15 Gold 79

Mass Number always a whole number NOT on the Periodic Table! mass # = protons + neutrons © Addison-Wesley Publishing Company, Inc. always a whole number NOT on the Periodic Table!

Mass Number Mass number (a) is the number of protons and neutrons in the nucleus of an isotope: Mass # = p+ + n0 Nuclide p+ n0 e- Mass # Oxygen - 10 - 33 42 - 31 15 18 8 8 18 Arsenic 75 33 75 Phosphorus 16 15 31

Symbols Nuclear symbol: Mass # Atomic # Hyphen notation: carbon-12

Symbols 17 37 20 Chlorine-37 atomic #: mass #: # of protons: # of electrons: # of neutrons: 17 37 20

Br Symbols 80 35 Find each of these: number of protons number of neutrons number of electrons Atomic number Mass Number 80 Br 35

Symbols If an element has an atomic number of 34 and a mass number of 78, what is the: number of protons number of neutrons number of electrons complete symbol

Symbols If an element has 91 protons and 140 neutrons what is the Atomic number Mass number number of electrons complete symbol

Symbols If an element has 78 electrons and 117 neutrons what is the Atomic number Mass number number of protons complete symbol

Isotopes Dalton was wrong about all elements of the same type being identical Atoms of the same element can have different numbers of neutrons. Thus, different mass numbers. These are called isotopes.

Isotopes Frederick Soddy (1877-1956) proposed the idea of isotopes in 1912 Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioactive materials.

Isotopes © Addison-Wesley Publishing Company, Inc.

Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons. Protons Electrons Neutrons Nucleus Hydrogen–1 (protium) 1 Hydrogen-2 (deuterium) Hydrogen-3 (tritium) 2

Isotopes Elements occur in nature as mixtures of isotopes. Isotopes are atoms of the same element that differ in the number of neutrons.

Composition of the nucleus Atomic Masses Atomic mass is the average of all the naturally occurring isotopes of that element. Isotope Symbol Composition of the nucleus % in nature Carbon-12 12C 6 protons 6 neutrons 98.89% Carbon-13 13C 7 neutrons 1.109% Carbon-14 14C 8 neutrons 0.001% Carbon = 12.011

Average Atomic Mass Avg. Atomic Mass weighted average of all isotopes on the Periodic Table Avg. Atomic Mass

Average Atomic Mass EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. Avg. Atomic Mass 16.00 amu

Average Atomic Mass EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. Avg. Atomic Mass 35.40 amu