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The AtomAtomic Number and Mass

NumberIsotopes

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Atomic Theory

Atoms are building blocks of elements

Similar atoms in each element

Different from atoms of other elements

Two or more different atoms bond in simple ratios to form compounds

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Subatomic Particles

Particle Symbol Charge RelativeMass

Electron e- 1- 0

Proton p+ + 1

Neutron n 0 1

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Location of Subatomic Particles

10-13 cm electrons

protons neutrons

10-8 cm

nucleus

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Atomic Number

Counts the number of

protonsin an atom

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Periodic Table

Represents physical and chemical behavior of elements

Arranges elements by increasing atomic number

Repeats similar properties in columns known as chemical families or groups

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Periodic Table

1 2 3 4 5 6 7 8

11 Na

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Atomic Number on the Periodic Table

11Na

Atomic Number

Symbol

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All atoms of an element have the same number of protons

11Na

11 protons

Sodium

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Learning Check AT 1

State the number of protons for atoms of each of the following:A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons

B. Sulfur 1) 32 protons 2) 16 protons 3) 6 protons

C. Barium1) 137 protons 2) 81 protons 3) 56 protons

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Solution AT 1

State the number of protons for atoms of each of the following:A. Nitrogen 2) 7 protons B. Sulfur

2) 16 protons

C. Barium3) 56 protons

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Number of Electrons

An atom is neutral The net charge is zeroNumber of protons = Number of electronsAtomic number = Number of electrons

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Mass Number

Counts the number of

protons and neutronsin an atom

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Atomic Symbols

Show the mass number and atomic number

Give the symbol of the element

mass number 23 Na sodium-23

atomic number 11

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More Atomic Symbols

16 31 65 O P Zn 8 15 30

8 p+ 15 p+ 30 p+

8 n 16 n 35 n8 e- 15 e- 30 e-

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Masses of AtomsA scale designed for atoms gives their small

atomic masses in atomic mass units (amu)An atom of 12C was assigned an exact mass of

12.00 amuRelative masses of all other atoms was

determined by comparing each to the mass of 12C

An atom twice as heavy has a mass of 24.00 amu. An atom half as heavy is 6.00 amu.

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Atomic Mass

Listed on the periodic tableGives the mass of “average” atom of each

element compared to 12C Average atom based on all the isotopes and their

abundance %Atomic mass is not a whole number

Na22.99

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Learning Check AT6

Using the periodic table, specify the atomic mass of each element (round to the tenths place): A. calcium __________B. aluminum __________C. lead __________D. barium __________E. iron __________

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Solution AT6

Using the periodic table, specify the atomic mass of each element (round to the tenths place):A. calcium _40.1 amu _ B. aluminum _27.0 amu _ C. lead _207.2 amu_D. barium _137.3 amu_E. iron _55.8 amu__