4-2 Notes Discovering Parts of the Atom Chapter 4, Lesson 2

4-2 Notes Discovering Parts of the Atom

Chapter 4, Lesson 2

So...... a neutron walks into Starbucks and orders a drink.

The barista promptly serves him his drink.

"How much will that be?" asks the neutron.

"For you?" replies the barista, "no charge!"

(get it?)

Thomson - Electrons

• In 1897, English scientist J.J. Thomson discovered electrons while doing an experiment to see how electric currents affected cathode rays.

Thomson - Electrons• A cathode ray is a stream of particles that

can be seen when an electric current passes through a vacuum tube.

• The ray travels from a negatively charged disk at one end to a positively charged disk at the other end.

Thomson - Electrons

• Thomson discovered the cathode rays did not travel in a straight line, but bent towards the positively charged plate.

Thomson - Electrons

• Opposite charges attract, so cathode ray particles must be negative if they are attracted to something positive.

• He named the particles electrons.

Thomson - Electrons

• He also said (like Dalton), that an atom was a solid sphere

• He added that an atom had a positive charge spread evenly throughout, with electrons mixed in to balance the charge.

Rutherford – Nucleus (Protons & Neutrons) (1899)

• Students of Ernest Rutherford shot alpha particles (protons + neutrons) through gold foil.

Rutherford – Nucleus (Protons & Neutrons) (1899)

2 protons bound to 2 neutrons

(a Helium nucleus)

http://upload.wikimedia.org/wikipedia/commons/d/d7/Alphadecay.jpg

• Rutherford thought the path of the alpha particles would bend only slightly because there was not anything big enough to strongly repel them.

Rutherford – Nucleus (Protons & Neutrons)

• Most particles did pass straight through.

• Some particles were strongly bounced to the side.

• One in about 8000 bounced completely backwards.


• Rutherford believed the alpha particles were hitting something with a positive charge and relatively large mass.


• He revised the atomic model: The atom is mostly empty space with the nucleus in the middle.

• He discovered the proton, and predicted the existence of the neutron.

• His model did not accurately explain how electrons are arranged in the atom.


Bohr - Hydrogen Atom (1913)

• A Danish scientist, Niels Bohr, studied the hydrogen atom and then proposed a new model for the arrangement of electrons in an atom.

Bohr studied under bothThomson and Rutherford.

Bohr - Hydrogen Atom

• Bohr thought electrons traveled in circles with a certain diameter.

• Bohr studied hydrogen because it has only one electron.

• When atoms are excited, they absorb and release energy in the form of light.


• A spectral line is a single wavelength of light that can be seen when the light from an excited element is passed through a prism.

• When excited, hydrogen and neon give off unique narrow bands of light on the spectrum.


• An energy level is a region in space corresponding to a certain energy through which an electron moves (similar to a planet’s orbit).


• He said that electrons move in specific orbits that are a set distance outside the nucleus.

• Each energy level can hold a certain number of electrons according to these rules:

Bohr’s Model


– The first level holds 2 electrons, the second level holds 8 electrons.

Neon’s atomic number = 10It has 10 protons.It has 10 electrons.

10NeNeon20.18


– The lowest level is filled first.

Ne

10NeNeon20.18



Ne

10NeNeon20.18



Ne

10NeNeon20.18


– The second level has no electrons until the first level is full.

10NeNeon20.18

Ne



10NeNeon20.18

Ne



10NeNeon20.18

Ne



10NeNeon20.18

Ne



10NeNeon20.18

Ne



10NeNeon20.18

Ne



10NeNeon20.18

Ne



10NeNeon20.18

Ne



10NeNeon20.18

Ne


– The last energy level may or may not be filled to the max.

Ne

10NeNeon20.18

3Li

Lithium6.94

Li


• An element will react with other elements to try to receive a full outer energy level. (also known as “completing the octet”)


• This diagram shows how electrons are placed in the elements with atomic numbers 1–10 (according to Bohr’s model)


• Different numbers of electrons in outer energy level results in different elements.

• Unreactive elements have a full outer energy level.

• Elements with incomplete outer energy levels are likely to form compounds.


Atomic Model

http://glencoe.mcgraw-hill.com/sites/0078741858/student_view0/brainpop_movies.html#

http://glencoe.mcgraw-hill.com/sites/0078741858/student_view0/brainpop_movies.html

Modern - Electron Cloud Model

• Today scientists think of an electron in an atom as being in an electron cloud, which is a region surrounding an atomic nucleus where an electron is most likely to be found.

Electron Cloud Model

Modern - Electron Cloud Model

• Electrons are more likely to be near the nucleus because they are attracted to the positive charge of the protons.

An excited hydrogen atom emits narrow bands of light called ____.

A energy lines

B wave lines

C spectral lines

D wavelengths

4.2 Discovering Parts of the Atom

1. A

2. B

3. C

4. D

Elements that do not react with other elements must have ____.

A completely filled energy levels

B excited electrons

C empty energy levels

D the same number of protons and neutrons


1. A

2. B

3. C

4. D

In the gold foil experiment, why did some particles pass straight through the foil?

A because they were repelled by the protons in the foil

B because they were attracted by the protons in the foil

C because atoms have no effect on charged particles

D because atoms are mostly empty spaces


1. A

2. B

3. C

4. D

Atoms of the same element always have the same number of ____.

A electrons

B neutrons

C ions

D protons

An electron moves into a higher energy level. What must have happened?

A The electron released energy.

B The electron absorbed energy.

C The atom gained a negative charge.

D The atom gained a positive charge.

A spectral line is caused by ____.

A an excited electron releasing energy and falling to a lower energy level

B an excited electron absorbing electricity and jumping to a higher energy level

C an atom gaining an ionic charge

D an atom losing a proton

4-2 VocabText p. 182-194

1. charge

2. Thomson's Atomic model

3. research

4. Rutherford's Atomic model

5. visible

6. spectral line

7. energy levels

8. Bohr's Atomic model

9. electron cloud

10.electromagnetic spectrum

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4-2 Notes Discovering Parts of the Atom Chapter 4, Lesson 2