Unit 4 Properties of Atoms and the Periodic Table

Protons and neutrons have been broken down into smaller particles called

• nuclei.

• quarks.

• electrons.

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The positively charged center of an atom is called a(n)

• neutron.

• proton.

• nucleus.

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The particle of an atom that is electrically neutral is called the

• electron.

• nucleus.

• neutron.

This English scientist offered proof that atoms existed in the 19th century.

• Democritus

• John Dalton

• Ernest Rutherford

The model of an atom that is represented by tiny, solid particles like the image shown is the

• Democritus Model.

• Bohr Model.

• Thomson Model.

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The atomic mass of an element is

• the number of protons in each atom.

• the average mass of atoms of that element.

• the number of protons plus the number of neutrons of an atom.

The atomic number of an element is the number of _______ of an atom of that element.

• protons in the nucleus

• protons plus neutrons in the nucleus

• electrons in the nucleus

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The atomic number of manganese is 25; its mass number is 55. How many neutrons

does an atom of manganese have in its nucleus?

• 80

• 30

• 55

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________ are atoms of the same element that have different numbers of neutrons.

• Compounds

• Ions

• Isotopes

The atomic number of Re is 75. The atomic mass of one of its isotopes is 186. How many neutrons are in an atom of this isotope?

• 111

• 186

• 75

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