Structure of the Nuclear Atom

What is everything made of?

The Atom

A. The atom is the smallest particle of an element that retains its properties of the element.

What culture was the first to come up with the idea of an atom?

History of the Atom

A. Democritus

1. Democritus (460 B.C. – 370 B.C) was the first to suggest the existence of atoms

2. Democritus believed atoms were indivisible and indestructible

• What are some ideas that he missed?

B. Dalton’s Atomic Theory1. All elements composed of

indivisible particles called atoms

2. Atoms of the same element are identical

3. Atoms of different elements can physically mix together or chemically combine in simple whole-number ratios to form compounds.

4. Chemical reactions occur when atoms are separated, joined, or rearranged.

• How big is an atom?

• What are things we use to see small things? What are some different types?

lll. Size of the Atom

A. The radii of most atoms range from 5 x 10-11m to 2 x 10-10m

B. Individual atoms are observable with instruments such as a scanning tunneling microscope.

Question Time

• What is an atom?• Who is Democritus?• What are the four ideas of Dalton’s

Atomic Theory?• What is the size of most atoms?• What do scientists use to see an

atom?

Does an atom normally have a charge?

What are subatomic particles?

Can atoms have a charge?

lV. Atoms and Their Charges

A. Atoms have no net electrical charge, they are electrically neutral

B. Electric charges are carried by particles of matter (subatomic particles)

C. Electric charges always exist in whole-number multiples. (no fractions )

D. When a given number of negatively charged particles combines with an equal number of positively charged particles, an electrically neutral particle is formed

What are the subatomic particles?

What are their charges?

V. Subatomic Particles

A. There are three kinds of subatomic particles. These particles make up the atom.

1. Electrons (negative)2. Protons (positive)3. Neutrons (neutral)

What do we know about electrons?

B. Electrons1. Electrons are negatively charged

2. One electron carries one unit of negative charge

3. Has a mass of 1/1840 of a hydrogen atom

4. Symbol for and electron is e or e-

What do we know about protons?

C. Protons

1. Protons are positively charged subatomic particles

2. Each proton has a mass about 1840 times that of an electron

3. Symbol for a proton is p or p+

What do we know about neutrons?

D. Neutrons1. Neutrons are subatomic particles with no charge

2. Has a mass equal to that of a proton (1840 times of an election)

3. Symbol for a neutron is n or n0

Question Time

• What charge are atoms?• Are there fraction of charges?• What if there were nine positively charged

particles and eight negatively charged particles, what would the net charge of the atom be?

• What are the three subatomic particles and what are their charges?

• What is the mass of an electron compared to a hydrogen atom?

• What is the mass of a proton compared to a neutron?

Vl. J.J. Thompsons’s Plum Pudding ModelA. When subatomic particles were

discovered, scientist wondered how these particles were put together in an atom.

B. J.J. Thompson thought that electrons were evenly distributed throughout. An atom was filled uniformly with positively charged material called the “plum-pudding” model or “chocolate cookie dough” model

Vll. Rutherford’s Gold Foil Experiment

A. In 1911 Ernest Rutherford wanted to study the structure of the atom as well. The plum-pudding model was the prevailing theory back then

B. In his experiment he used alpha particles, which are helium atoms that have lost their two electrons.

C. Then, directed the alpha particles at a very thin sheet of gold foil. The particles should have passed easily through the gold with a slight deflection due to the positive charge thought to be spread out in the gold atomsWhat do you think happened?

D. The great majority of alpha particles passed straight through the gold atoms, without deflection

E. A small fraction of the alpha particle bounced off the gold foil at large angles.

F. Based on the experimental results Rutherford suggested that the atoms were mostly empty space, but had a dense center called the nucleus.

What does that mean?

G. Gold Foil Experiment Conclusion

1. All the positive charge and all the mass of the atoms was concentrated in a small region called the nucleus

2. “This is almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.” (Actual Quote)

What do we call the center of an atom?

What is in the center?

Vlll. The Nuclear AtomA. The nucleus is the central core of an atom

1. composed of protons and neutrons.

B. The nucleus is much smaller than the atom, yet contains most of its mass

C. The electrons are distributed around the nucleus

1. occupy almost all the volume of the atom 2. Most of the atom is made up of empty

space.

lX. Fun Facts

A. The volume of a hydrogen nucleus is a trillion times smaller than the volume of a hydrogen atom, yet the nucleus contains most of the mass.

B. If the nucleus (proton) of a hydrogen atom were as large as the width of a human thumb, the electron would be on the average about one kilometer away in a great expanse of empty space.

Question Time• What is the plum-pudding model and who

thought of it?• Is the plum-pudding model correct?• What happened in the gold foil experiment?• What did the gold foil experiment prove?• Where is the positive charge located in the

atom?• What contains most of the mass of the

atom?• What occupies most of the volume of the

atom?• What is the atom is mostly made up of?