Rutherford and the nucleus

British physicist who, in 1911, proved that atoms had a small, dense, positively charged nucleus.

Rutherford’s Model Protons ( the positively charged sub-

atomic particles ) are concentrated in a small area at the center of the atom.

He called this area the nucleus. An atom is mostly empty space. The nucleus is tiny compared to the

whole atom, but it contains nearly all the atom’s mass.

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Rutherford’s Model of the Atom

Limitation: did not specify exactly where the electrons were

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Bohr and energy levels

Danish scientist who, in 1913, proposed the “Planetary Model” of the atom

The energy levels occupied by electrons are like the orbits of planet at different distances from the sun.

Bohr compares electrons to the planets and nucleus to the sun.

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In 1932, James Chadwick discovered the neutron.

The nucleus contains neutrons. A neutron has about the same

mass as a proton but has no electrical charge.

Jimmy neutron walked into a bar and  asked how much for a drink.  The bartender replied,  "for you, no charge." 

-Jaime - Internet Chemistry Jokes

Chadwick and the neutron4

Quantum Mechanical or Electron Cloud Model

Electrons dart about within an energy level in an ever – changing path.

Their rapid motion creates a “ cloud” of negative electricity around the nucleus.

The electron cloud gives an atom its size and shape.

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Electron Cloud Model

n nucleus

electron cloud

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Seatwork:

In size 4: start identifying the 5 suspects

In your SBP, draw the models of Dalton, Thomson, Rutherford, Bohr and the Quantum model. Label and write a short description about the model.

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Let us see if you got it right.

1. Dalton 2. Rutherford 3. Thomson

4. Bohr 5. Democritus

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Atomic Models

Dalton’s Atomic Model

Rutherford’s Atomic ModelThomson’s Atomic

Model

Electron Cloud Model

Bohr’s Planetary Atomic Model

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A CLOSER LOOK ON ATOMS

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ATOMS

Potential energy and kinetic energy are present in the atom

Atoms are always neutral in charge In an atom, no. of protons = no. of

electrons Atomic number:

Lower in amount than mass number Number of protons in an atom Tells you the identity of the element

Mass number/ Atomic weight/Atomic mass: Higher in amount than atomic munber Number of protons and neutrons in an

atom

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Computation in atoms

# of protons = Atomic number # of electrons = Atomic number # of neutrons = Mass number– Atomic

number Mass number = # of protons + # of neutrons

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Element

Mass Number

Atomic Number

Number of

Protons

Number of

Electrons

Number of

Neutrons

Li

Cu

Cl

Ag

Pb

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