Bohr Models

Bohr Models

Middle School

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Learning Objectives

• Describe Bohr's atomic model and its improvements on earlier models.

• Explain energy levels, quanta, and how electrons can move between them.

• Draw a Bohr model for an element using the periodic table.

• Define valence electrons and explain their role in an element's chemical reactivity.

Key Vocabulary

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Bohr's Atomic Model

A model where electrons orbit the nucleus at fixed distances called energy levels, based on their energy.

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Energy Levels

These are fixed distances from the nucleus where electrons may orbit, also known as electron shells.

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Quantum

This is the minimum amount of energy that matter can absorb or release, a discrete packet of energy.

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Valence Electrons

These are the electrons in the outermost shell of an atom, which determine its reactivity with other elements.

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Building on the Atomic Model

Early Models

• J.J. Thomson's model pictured electrons scattered within a sphere of positive charge.

• Ernest Rutherford proposed a central nucleus with electrons orbiting it like planets.

• This model didn't clarify where electrons were in the space around the nucleus.

Bohr's Model

• In 1913, Niels Bohr proposed a new, more detailed atomic model.

• He suggested that electrons were not just orbiting the nucleus randomly.

• His work was a major step forward in understanding atomic structure.

Multiple Choice

What was the main weakness in Rutherford's atomic model that Niels Bohr's model addressed?

• The location and behavior of electrons

• The existence of the nucleus

• The positive charge of the atom

• The presence of neutrons

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Energy Levels and Quantum Leaps

• Electrons orbit the nucleus at fixed distances called energy levels or shells.

• ​Like rungs on a ladder, an electron cannot be between energy levels.

• To jump to a higher level, an electron absorbs a quantum of energy.

• To fall to a lower level, it must release that same quantum.

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Multiple Choice

According to Bohr's model, what must happen for an electron to jump to a higher energy level?

• It must absorb a specific quantum of energy.

• It must release a specific quantum of energy.

• It must touch the nucleus.

• It must move in between two energy levels.

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How to Draw a Bohr Model

• Draw the nucleus with the number of protons and neutrons written inside.

• Draw the first energy shell, which holds a maximum of two electrons.

• Draw the second energy shell, which can hold a maximum of eight electrons.

• Continue adding shells, filling them with electrons from the innermost shell outward.

Multiple Choice

What is the maximum number of electrons that can be held in the first and second energy shells, respectively?

• 2 and 8

• 8 and 2

• 2 and 2

• 8 and 8

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Valence Electrons and Reactivity

• Valence electrons are in the outermost shell of an atom.

• These electrons are the ones involved in chemical reactions.

• Reactivity is how likely an element is to form a compound.

• The number of valence electrons determines an element's reactivity.

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Multiple Choice

What is the primary role of valence electrons in an atom?

• They determine the atom's chemical reactivity.

• They contribute to the atom's mass.

• They are located in the nucleus.

• They hold the protons and neutrons together.

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Common Misconceptions

Misconception	Correction
Electrons can orbit anywhere around the nucleus.	Electrons are restricted to fixed energy levels and cannot exist between them.
Electrons fill outer shells before the inner shells are full.	Electrons fill the lowest energy levels (closest to the nucleus) first.
The nucleus of an atom is involved in chemical reactions.	Only the valence electrons are involved in chemical reactions.

Multiple Choice

Why is Bohr's model of the atom often compared to a ladder?

• It explains that electrons must exist on specific energy levels (rungs) and cannot be in between them.

• It explains that electrons are always climbing to higher energy levels.

• It explains that the nucleus is at the bottom of the ladder.

• It explains that atoms are built upwards from the nucleus.

Multiple Choice

An element has an atomic number of 11. How would its electrons be arranged in the energy shells according to the Bohr model?

• 2 electrons in the first shell, 8 in the second shell, and 1 in the third shell.

• 2 electrons in the first shell and 9 in the second shell.

• 11 electrons all in the first shell.

• 8 electrons in the first shell and 3 in the second shell.

Multiple Choice

Fluorine has 9 electrons, with 7 in its outer shell. Neon has 10 electrons, with 8 in its outer shell (a full shell). Which element is more reactive and why?

• Fluorine is more reactive because it wants to gain one electron to have a full outer shell.

• Neon is more reactive because it has more total electrons.

• Fluorine is less reactive because it has fewer electrons.

• They are equally reactive because they are both nonmetals.

Multiple Choice

If an electron in the second energy level loses a specific quantum of energy, what would likely happen to it?

• It would move down to the first energy level.

• It would move to the third energy level.

• It would be ejected from the atom completely.

• It would stay in the second energy level but spin faster.

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Summary

• Bohr's model places electrons in fixed energy levels or shells around the nucleus.

• Electrons can jump between levels by absorbing or releasing a specific amount of energy.

• The first electron shell holds up to 2 electrons; the second holds up to 8.

• Valence electrons determine an element's chemical reactivity; atoms with a full outer shell are stable.

Poll

On a scale of 1-4, how confident are you about drawing Bohr models for elements?

• 1

• 2

• 3

• 4