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Review of Atomic Model

How does the modern atomic theory describe the parts that make up the

atom? Atomic Number: Periodic Table

Atomic number : number of protons in the nucleus. This number is found above element on a periodic table.

Atomic Number: Symbol

The atomic number of an element is usually written on lower left corner of symbol.

Protons and Neutrons

Two particles in the nucleus: Protons have a positive charge. Neutrons do not have a charge.

Neutron Number

The following table shows the most common number of neutrons found in an element.

66

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Mass Number

Mass number refers to the total number of protons and neutrons. Example:fluorine: 9 protons 10 neutronsAtomic number is 9. Mass number is 9 + 10 = 19

Mass Number: SymbolThe mass number is written on upper left corner of element.

Electrons

Electrons have a negative charge and move outside the nucleus.The number of electrons is equal to the number of protons in a neutral atom.This lithium atom has3 protons and 3

electrons. Atomic

Mass

Atomic mass is stated in units called atomic mass units (amu). The symbol for 1 amu can be a “u ” or a .The amu is based on 12 C.1 amu is defined as 1/12 the mass of 12 C.

Atomic Mass Periodic Table

The atomic mass is found below the symbol for an element on the periodic table.

Atomic Mass Defined

The mass of 126C is said

to be 12 amu. One atomic mass unit(amu) is defined as being 1/12 the mass of 12 C. Hydrogen has a mass of 1 (1/12 the mass of 12

6C).Helium has a mass of 4 (4/12 the mass of 12

6C).

B

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Masses of Particles

A proton is a “heavy” particle. It mass a mass of 1 .A neutron is also a “heavy” particle. It mass a mass very close to 1 .An electron is very very light. It has a mass of about 1/1837 , so sometimes we say that it has a mass of 0 (even though it does have some mass).

Checklist

1. Use the modern atomic theory to describe the meaning of the terms atomic number, mass number, atomic mass.2. Using the form A X, write the proper symbol for an element.3. Predict the number of protons, electrons, and neutrons knowing the atomic number and mass number of an atom.4. State the charge, location, and mass of the subatomic particles.

uraniumuranium

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