Structure of AtomsStructure of Atoms

Chapter 3 section 2Chapter 3 section 2

Structure of atomsStructure of atoms

Ms.BrionesMs.Briones

Subatomic particlesSubatomic particles

Experiments by several scientists in the Experiments by several scientists in the mid-1800s led to the first change to mid-1800s led to the first change to Dalton’s atomic theory.Dalton’s atomic theory.

Scientists discovered that atoms can be Scientists discovered that atoms can be broken into pieces.broken into pieces.

The most important particles:The most important particles:

ElectronElectron

Proton Proton

NeutronNeutron

Electrons Electrons

Electrons were discovered by using Electrons were discovered by using cathode rays (just like in a TV)cathode rays (just like in a TV)

J.J. Thomson, scientist, created the J.J. Thomson, scientist, created the cathode rays.cathode rays.

What was Thomson’s creation?What was Thomson’s creation?

He pumped the air out of glass tube.He pumped the air out of glass tube. He then applied a voltage to 2 metal He then applied a voltage to 2 metal

plates, called electrodes which were plates, called electrodes which were placed at each end of the tube (positive placed at each end of the tube (positive and negative charges).and negative charges).

What was Thomson’s creation?What was Thomson’s creation?

Thomson observed a glowing beam that Thomson observed a glowing beam that came out of the cathode and struck the came out of the cathode and struck the anode (+). anode (+).

He called these the cathode rays.He called these the cathode rays. Now it is used for many devices.Now it is used for many devices.

ElectronsElectrons

They are part of an atom.They are part of an atom. They are negatively charged.They are negatively charged. Common charge notation: -1Common charge notation: -1 Symbol: Symbol: ee Located in the outer energy level.Located in the outer energy level.

RutherfordRutherford

Rutherford, also a Rutherford, also a scientist, studied scientist, studied Thomson’s theory and Thomson’s theory and carried out the carried out the experiment.experiment.

The NucleusThe Nucleus

Rutherford discovered the nucleus in his Rutherford discovered the nucleus in his model called the plum-pudding model.model called the plum-pudding model.

Also called alpha particles

RutherfordRutherford

Gold Foil Experiment

Conclusion: mass of nucleus must be larger than the alpha particle

The NucleusThe Nucleus

The nucleus is the dense, central portion The nucleus is the dense, central portion of the atom. of the atom.

Contains most of the mass and a small Contains most of the mass and a small fraction of the volumefraction of the volume

Protons and NeutronsProtons and Neutrons

Protons: + charge Protons: + charge (+1)(+1)

Neutrons: neutral Neutrons: neutral charge (0)charge (0) In the nucleusIn the nucleus

Protons and Neutrons can form a Protons and Neutrons can form a stable nucleus.stable nucleus.

Coulomb’s lawCoulomb’s law: the : the closer two charges are, closer two charges are, the greater the force the greater the force between them. between them. (magnets)(magnets)

Atomic number and mass numberAtomic number and mass number

All atoms consist of protons and electrons.All atoms consist of protons and electrons. Most atoms also have neutrons.Most atoms also have neutrons. Elements differ from each other in the Elements differ from each other in the

number of protons their atoms contains.number of protons their atoms contains. To know the atomic number of an atom To know the atomic number of an atom

you look at the number of protons.you look at the number of protons. Example: Oxygen = 8 protons = 8 Example: Oxygen = 8 protons = 8

atomic numbers.atomic numbers.

Atomic number and mass numberAtomic number and mass number

Mass numberMass number

The mass number is equal to the total The mass number is equal to the total number of particles of the nucleus (the number of particles of the nucleus (the total number of protons and neutrons). total number of protons and neutrons).

Atomic mass – atomic number: number of neutrons.

Useful notesUseful notes

Atomic number = number of Atomic number = number of protons = number of electrons.protons = number of electrons.

Mass number – atomic number = Mass number – atomic number = number of neutrons.number of neutrons.

Example:Example:

Neon: 10 Neon: 10 protonsprotons, 10 , 10 neutronsneutrons, and 10 , and 10 electrons. What is the mass electrons. What is the mass number:_____number:_____

Activity page 86,Activity page 86, Questions 1-4 (pg.86)Questions 1-4 (pg.86)

Isotopes of an element have the Isotopes of an element have the same atomic number.same atomic number.

Isotopes: atoms of the same element that Isotopes: atoms of the same element that have different numbers of neutrons are have different numbers of neutrons are called isotopes.called isotopes.

Example: Example:

1 neutron

2 neutrons

Two standard ways to identify Two standard ways to identify isotopesisotopes

11stst: to write the : to write the mass numbermass number with a with a hyphen after the name of an element. hyphen after the name of an element.

Example: helium-3, helium-4Example: helium-3, helium-4 22ndnd: shows the composition of a nucleus as : shows the composition of a nucleus as

the isotope’s nuclear symbol. the isotope’s nuclear symbol.

Example: 3/2 HeExample: 3/2 He

Did you know?Did you know?

The image on a TV The image on a TV screen or a computer screen or a computer is produced when is produced when cathode rays strike the cathode rays strike the special coating on the special coating on the inside of the screen.inside of the screen.