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Chapter 5 Electrons in Atoms

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Chapter 5 Electrons in Atoms

5.1 Models of the Atom

- Today we are learning to:-1. Realize there were problems with Rutherford’s model of the atom2. Understand the new ideas put forward in Bohr’s model of the atom
- 3. Describe what is meant by a quantum mechanical model
- 4. Describe what is meant by quantum energy sub levels

Development of Atomic Models

- Rutherford’s model fails to explain why objects change color when heated.
- According to Maxwell’s electromagnetic theory, this model was unstable. Electrons should spiral in towards the nucleus within a fraction of a second
- A new model was needed

5.1

Development of atomic models from 1803 to 1911.

5.1

Development of atomic models from 1913 to 1932.

The Bohr Model

- Niels Bohr improved on Rutherford’s model in 1913. In his model:
- Each possible electron orbit has a fixed energy level.
- An electron is only allowed in an energy level, not in between.
- An electron can jump between levels
- Higher energy levels tend to be further from the nucleus.
- A quantum of energy is the amount of energy required to make an electron jump between levels.

The Bohr Model

- Like the rungs of the strange ladder, the energy levels in an atom are not equally spaced.
- The higher the energy level occupied by an electron, the less energy it takes to move from that energy level to the next higher energy level.

The Quantum Mechanical Model

- In 1926 Erwin Schrodinger developed mathematical equations describing the behavior of an electron in a hydrogen atom
- The modern description of the electrons in atoms, the quantum mechanical model, comes from the mathematical solutions to the Schrödinger equation.
- Solutions give a probability of finding an electron in a certain position

The Quantum Mechanical Model

- In 1926 Erwin Schrodinger developed mathematical equations describing the behavior of an electron in a hydrogen atom
- The modern description of the electrons in atoms, the quantum mechanical model, comes from the mathematical solutions to the Schrödinger equation.
- Solutions give a probability of finding an electron in a certain position

Atomic Orbitals

- An atomic orbitalis often thought of as a region of space in which there is a high probability of finding an electron.
- Principal energy levels are labelled with the quantum numbersn=1, n=2, n=3, n=4 etc. …………
- Each energy sublevel l=1, l=2, l=3, l=4, l=5, corresponds to an orbital of a different shape, which describes where the electron is likely to be found.
- The sublevels are given letters to describe them.
- l=1=s orbital
- l=2=p orbital
- l=3=d orbital
- l=4=f orbital

Atomic Orbitals

Each energy sublevel relates to orbitals of different shape.

Atomic Orbitals

1.Rutherford's planetary model of the atom could not explain

- any properties of elements.
- the chemical properties of elements.
- the distribution of mass in an atom.
- the distribution of positive and negative charges in an atom.

2.Bohr's model of the atom proposed that electrons are found

- embedded in a sphere of positive charge.
- in fixed positions surrounding the nucleus.
- in circular orbits at fixed distances from the nucleus.
- orbiting the nucleus in a single fixed circular path.

3.What is the lowest-numbered principal energy level in which porbitals are found?

- 1
- 2
- 3
- 4

5.1Vocabulary

- Energy levels:possible electron orbits in Bohr’s model of the atom
- Quantum:small whole number unit of energy
- Quantum mechanical model: quantum description of the movement of electrons in atoms obtained from solving Schrodinger’s equations
- Atomic orbital: region of space where there is a high probability of finding an electron

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