• Describe the mass, charge, and location of protons, neutrons, and electrons in atoms.

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SPS1 Students will investigate our current understanding of the atom.a. Examine the structure of the atom in terms of

- proton, electron, and neutron locations- Atomic mass and atomic number- Atoms with different numbers of neutrons (isotopes)- Explain the relationship of the proton number to the elements identity

Chapter 4

Atomic Structure

What was Dalton’s theory of the structure of matter?What contributions did Thomson and Rutherford make to the development of atomic theory?

4.1 Studying Atoms

• Democritus – (Greek) all matter is composed of small particles that can not be divided– Called atoms (uncut or indivisible)– Thought atoms had different shapes

• Liquids – round and smooth• Solids – rough and prickly

• Aristotle – (Greek) matter could be divided forever– Five elements (earth, water, air, fire, aether)

4.1 Studying AtomsWhat was Dalton’s theory of the structure of matter?

• John Dalton (England, 1700’s)– Noticed that elements in compounds

always came in specific ratios• Water – 8 oxygen to 1 hydrogen

– Developed a theory to explain

4.1 Studying AtomsWhat was Dalton’s theory of the structure of matter?

• Dalton’s Atomic Theory– All elements are composed of atoms– All atoms of the same element have the

same mass, and atoms of different elements have a different mass

– Compounds are composed of atoms of one or more elements

– For a specific compound, atoms of different elements combine in exactly the same way

4.1 Studying AtomsWhat was Dalton’s theory of the structure of matter?

• Thomson’s Model of the Atom– Cathode Ray Experiment– Beams moved toward positive, and away

from the negative• Particles must be negative (electrons)

– Atoms are neutral, so there must also be positive particles

• Plum Pudding Model – electrons are evenly scattered in a positively charged mass

4.1 Studying AtomsWhat contributions did Thomson and Rutherford make to the development of atomic theory?

Simulation

• Rutherford’s Atomic Theory– The gold foil experiment– Alpha particles (helium nucleus) shot at gold

foil• Most particles passed through the gold• Some bounced back as if they had run into

something

• Conclusion– The atom has a very small, dense nucleus of

positive charge (nucleus)– Electrons exist in the rest of the space

4.1 Studying AtomsWhat contributions did Thomson and Rutherford make to the development of atomic theory?

Simulation

• List the four postulates of Dalton’s Atomic Theory.

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• In the history of the study of the atom, what did each of the following do

• Democritus• JJ Thomson• Rutherford

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What are three subatomic particles?How are atoms of one element different from atoms of another element?What is the difference between two isotopes of the same element?

4.2 The Structure of the Atom

• Subatomic Particles– Proton – (Rutherford)

• Positively charged• In the nucleus• Relative mass is 1

4.2 The Structure of the AtomWhat are the three subatomic particles?

• Subatomic Particles– Electron – (Thomson)

• Negatively charged• Outside of the nucleus (electron cloud)• Relative mass is 1/1836 – so 0

4.2 The Structure of the AtomWhat are the three subatomic particles?

• Subatomic Particles– Neutron – (James Chadwick 1932)

• Neutral or no charge• In the nucleus• Relative mass is 1

4.2 The Structure of the AtomWhat are the three subatomic particles?

• Dalton – atoms of one element are different from atoms of another– Atomic Number

• Atoms of the same element have the same number of protons

• Atoms of different elements have different numbers of protons

• The number of protons is give by the Atomic Number

4.2 The Structure of the AtomHow are atoms of one element different from atoms of other elements?

• Dalton – atoms of one element are different from atoms of another– Mass Number

• The sum of the protons and neutrons in a atom

• Or neutrons = mass number – atomic number

• Periodic tables list the average atomic mass

4.2 The Structure of the AtomHow are atoms of one element different from atoms of other elements?

• Atoms of the same element have the same atomic number, but don’t necessarily have the same mass number– Isotope

• Of the same element• Same number of protons• Different neutrons so the mass number is different• Listed by element name and mass number

– Uranium – 238

• Basically no difference in chemical properties

4.2 The Structure of the AtomWhat is the difference between two isotopes of the same element?

• List the atomic number, mass number, number of protons, neutrons, electrons, and the name of the following elements.

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• There are three naturally occurring isotopes of Uranium, Uranium -238, Uranium -235, Uranium -234.

• In terms of subatomic particles, what is the same about these three?

• What is different?

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What can happen to electrons when atoms gain or lose energy?What model do scientists use to describe how electrons behave in atoms?What is the most stable configuration of electrons in an atom?

4.3 Modern Atomic Theory

• Bohr Model – The rest of models discuss location of

electrons– Bohr believed that electrons orbit around the

nucleus – Constant speed, fixed orbit– Energy levels – higher energy electrons were

further away from the nucleus• Energy was lost or gained to move between levels• Limited number of electrons were allowed in each

energy level

4.3 Modern Atomic TheoryWhat can happen to electrons when atoms gain or lose energy?

• Electron Cloud Model – Different energy levels– Represented by areas of probability

• Areas become larger with energy• Electrons can be anywhere in the probability area

– Orbital – probability area for a specific amount of energy• Called s, p, d, f• Energy levels hold 2, 8, 18, 32 electrons

maximum

4.3 Modern Atomic TheoryWhat model do scientists use to describe how electrons behave in atoms?

• Electron Configuration – The way the electrons are arranged in

different orbitals– Most stable when the electrons are in the

lowest possible energy states– This is called the Ground State

4.3 Modern Atomic TheoryWhat model do scientists use to describe how electrons behave in atoms?