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Atomic Number, Mass Number, Atomic Mass and Isotopes Mrs. Coyle Chemistry.

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Presentation on theme: "Atomic Number, Mass Number, Atomic Mass and Isotopes Mrs. Coyle Chemistry."— Presentation transcript:

1 Atomic Number, Mass Number, Atomic Mass and Isotopes Mrs. Coyle Chemistry

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3 Atomic Number (Z): is the number of protons in the nucleus of the atom. Z=#p

4 The number of protons (atomic number) determine the identity of an element.

5 Atoms have no overall electrical charge so, an atom must have as many electrons as there are protons in its nucleus.

6 The atomic number of an element also equals the number of electrons in a neutral atom of that element.

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8 Ex: Sodium  What is the atomic number of Sodium?  How many protons does sodium have?  How many electrons does sodium have?

9 Mass Number (A): The sum of the protons and neutrons in the nucleus. A=#p + #n

10 Notation

11 Other ways to write elements: ClCl-36 Atomic Number Mass Number

12 Nucleons: protons and neutrons

13 Isotopes of an element have different mass numbers because they have different numbers of neutrons, but they have the same atomic number.

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15 Example: Isotopes of Carbon and Hydrogen protium deuteriumtritium HH H Isotopes of Carbon Isotopes of Hydrogen

16 Atomic Mass Unit is a unit used to compare the masses of atoms and has the symbol u or amu.

17 1 amu or u is approximately equal to the mass of a single proton or neutron.

18 Carbon-12 Chemists have defined the carbon-12 atom as having a mass of 12 atomic mass units.

19 1 u = 1/12 the mass of a Carbon-12 atom.

20 Atomic Mass is the weighted average mass of all the naturally occurring isotopes of that element.

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