Atoms and their structure

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Since most of the particles went through, it was mostly empty.

Because the pieces turned so much, the positive pieces were heavy.

Small volume, big mass, big density.

This small dense positive area is the nucleus.

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Other pieces

Proton - positively charged pieces 1840 times heavier than the electron.

Neutron - no charge but the same mass as a proton.

Where are the pieces?

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Subatomic particles

Electron

Proton

Neutron

Name

Symbol

Charge

Relative

mass

Actual

mass (g)

e-

p+

n0

-1

+1

0

1/1840

1

1

9.11 x 10-28

1.67 x 10-24

1.67 x 10-24

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Structure of the Atom

There are two regions.

The nucleus.

With protons and neutrons.

Positive charge.

Almost all the mass.

Electron cloud- most of the volume of an atom.

The region where the electron can be found.

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Size of an atom

Atoms are small.

Measured in picometers, 10-12 meters.

Hydrogen atom, 32 pm radius.

Nucleus tiny compared to atom.

IF the atom was the size of a stadium, the nucleus would be the size of a marble.

Radius of the nucleus is near 10-15m.

Density near 1014 g/cm3.

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Counting the Pieces

Atomic Number = number of protons

# of protons determines kind of atom.

the same as the number of electrons in the neutral atom.

Mass Number = the number of protons + neutrons.

All the things with mass.

NOT on the periodic table

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Isotopes

Dalton was wrong.

Atoms of the same element can have different numbers of neutrons.

different mass numbers.

called isotopes.

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Symbols

Contain the symbol of the element, the mass number and the atomic number.

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Symbols

Contain the symbol of the element, the mass number and the atomic number.

X

Mass

number

Atomic

number

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Naming Isotopes

Put the mass number after the name of the element.

carbon- 12

carbon -14

uranium-235

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