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Atomic Model

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Atomic Model

The atomic model, which has changed over time, is the model used to describe the structure and composition of the atom. The atom as a component of the universe has been under extensive study to understand how atoms make up the universe.

The concept of the atom

The concept of the atom comes from a Greek philosopher named Democritus. He stated that all matter is made of indivisible particles called atoms surrounded by empty space. There were also some other theories until our modern idea of the atom was formulated in the 19th and 20th centuries.

The composition of the atom

In the classical model, the atom is composed of smaller particles with an electrical charge known as electrons and protons. The atom also features a third, neutral kind of particle known as neutrons. Atomic models seek to understand how these particles make up the atom. The classical atom composition is as follows:

ParticleProtonElectronNeutron
Elemental charge+1-10
Symbolpen

Modern models of the atom see the positive charge as concentrated in a small space at the centre, i.e., in the atoms nucleus. Here, protons and neutrons are held together thanks to the strong nuclear force, which prevents the protons from repelling each other.

What are the five models of the atom?

There are five principal models of the atom that have been proposed over time, each being related to the understanding of the atom at the time. The models are: Dalton’s atomic model, Thomsons atomic model, Rutherfords atomic model, Bohr’s atomic model, and the quantum atomic model.

Dalton’s atomic model

John Dalton was an English scientist who proposed the first modern atomic model. He proposed that all matter is made of atoms, which are indivisible. Here are some of the properties Dalton associated with the atom:

  • All atoms of the same element have the same mass.
  • Atoms cannot split into smaller particles.
  • When any chemical reaction occurs, atoms rearrange.
  • Molecules are composed of several kinds of atoms of each different element, and chemical compounds have different ratios of elements.

Atomic Model. Dalton’s atomic model. StudySmarter Figure 1. Daltons atomic model proposed that atoms were indivisible and different for each element. Source: Manuel R. Camacho, StudySmarter.

Thomsons atomic model

With the discovery of electrons by British scientist J. J. Thomson, it became clear that the atom consisted of even smaller particles that were responsible for moving electrical charge.

Scientists during Thomsons time thought that atoms were essentially neutral. Thomson proposed that atoms had small negative particles floating above a fluid of positive charge. This model is also known as the plum pudding model.

Atomic Model. Thomson’s Atomic Model. StudySmarterFigure 2. Thomsons atomic model proposed a soup charged positively with the electrons floating on top. Source: Manuel R. Camacho, StudySmarter.

Rutherford’s atomic model

A New Zealand scientist named Ernest Rutherford designed some experiments together with German scientist Hans Geiger. The experiments, carried out by a student named Ernest Marsden, fired particles against a thin foil made of gold.

If the atom was a solid blob made of positive charge with some electrons on top, as Thomson’s atomic model proposed, most of the fired particles would not reach the other side of the foil. However, the experiment proved that Thomson was wrong. The atom was almost empty inside, as not many particles fired against the foil impacted the nuclei of the atoms.

Rutherford proposed that the atom contains a nucleus, with all the positive charges concentrated in the centre. In the model, the electrons were orbiting around the centre.

Atomic Model. Rutherford atomic model. StudySmarterFigure 3. Rutherfords atomic model proposed that electrons move around the nucleus in orbits. Source: Manuel R. Camacho, StudySmarter.

Bohrs atomic model

Rutherfords model did not gain full acceptance. Knowing that moving charges release energy as electromagnetic radiation, electrons should lose their kinetic energy. After losing their kinetic energy, electrons should then fall into the nucleus attracted by the electrostatic force. Inconsistencies in Rutherfords atomic model led a Danish scientist named Niels Bohr to propose a new one.

Bohr’s atomic model was similar to Rutherfords. The difference between the two concerns the question of how electrons move. According to Bohr, electrons can only travel in certain orbits, depending on their energy level, and they can move up and down the orbits releasing or absorbing energy. The rules proposed by Bohr are as follows:

  • Electrons can occupy certain orbits, depending on their energy level.
  • Each orbit has a certain energy level.
  • When jumping between orbits, energy must be absorbed or released by the electrons.
  • The energy emitted as a form of radiation can be calculated by the difference in energy levels between the orbits. This energy is said to be quantised.

Atomic Model. Bohr’s atomic model. StudySmarterFigure 4. Bohrs atomic model proposed that the electrons move around the atom in orbits and also jump to different orbits, depending on their energy level. The energy of each level has a fixed value, and electrons jump up and down, absorbing or releasing radiation. Source: Manuel R. Camacho, StudySmarter.

Bohrs model could explain a hydrogen atom whose electron is unique in not interacting with other electrons orbiting the atom. However, it failed to explain more complex elements or effects.

The quantum atomic model

The quantum atomic model is the most detailed model so far of how the atom is composed and how it works. It was developed with contributions by Erwin Schrödinger, Werner Karl Heisenberg, and Louis de Broglie. The model is an extension of Bohrs model by adding the concept of wave-particle duality, and it is able to explain more complex atoms than hydrogen.

The quantum model proposes that matter can behave as waves and that electrons move around the atom in orbitals. The orbital is a region in which there is a higher probability of an electron moving. In this model, electrons cannot be located precisely, and the orbitals are defined as clouds of probability.

Atomic Model. Quantum atomic model. StudySmarterFigure 5. An atom showing four orbitals, i.e., clouds where electrons could be present. Source: Manuel R. Camacho, StudySmarter.

Atomic Model - Key takeaways

  • The atomic model has passed through various stages of development with different understandings of the structure and composition of the atom.
  • Greek philosopher Democritus understood all matter to be composed of the same small objects called atoms.
  • Dalton’s model suggested that chemical reactions were the result of re-arrangements in the atoms that compose the object.
  • Successive atomic models, such as those proposed by Thomson and Rutherford, changed the way we think about the atom’s charge, as they included electrical charges and described how these were distributed in the atom.
  • Bohr’s model and the quantum atomic model changed the way we see the atoms nature and how electrons interact within it. In Bohr’s model, electrons move between orbits, depending on their energy levels. The quantum model introduced uncertainties in that electrons are understood to be moving in defined areas without us being able to locate their position beyond the probability of them existing in a certain position.

Frequently Asked Questions about Atomic Model

It is the name given to Thomson’s atomic model.

The better known atomic models are Dalton’s atomic model, Thomson’s atomic model, Rutherford’s atomic model, Bohr’s atomic model, and the quantum atomic model.

The current atomic model is the quantum mechanical model of the atom.

The atomic model is a representation of the atom. In this representation, we can know its properties such as mass, charge, composition, and how it exchanges energy and matter.

Final Atomic Model Quiz

Question

What is an atomic model?

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Answer

All answers are correct.

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Question

What is the classical composition of the atom?

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Answer

Classically, the atom consists of protons, neutrons, and electrons.

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What is the elemental charge of a proton?

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Answer

Plus one.

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What is the elemental charge of a electron?

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Answer

Minus one.

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 What is the elemental charge of a neutron?

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Answer

Zero.

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Question

Can you name the symbols for the neutron, proton, and electron?

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Answer

n, p, and e.

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What is the name of the first philosopher to propose atoms?

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Answer

Democritus.

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What did Democritus state regarding the atom?

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Answer

That all matter is made of indivisible particles called atoms.

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Question

Name the five better known atomic models.

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Answer

Dalton model, Thomson model, Rutherford model,  Bohr model, and quantum model.

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Thomson’s model is also known as …

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Answer

The plum pudding model.

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Thomson’s model proposed that electrons float above the nucleus. True or false?

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Answer

True.

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What was the nucleus made of according to Thomson?

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Answer

A soup of positive charge.

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Question

What is the difference between the models by Thomson and Rutherford?

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Answer

Both answers are correct.

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Question

Does Dalton’s model include the understanding that atoms of the same elements have the same mass?

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Answer

Yes, it does.

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Question

Is it true that, according to Rutherford, electrons move around the nucleus?

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Answer

Yes, it is.

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Question

Is there a relationship between the electron orbits and the energy in Bohr’s model?

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Answer

Yes, there is, as the orbit depends on the energy.

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Question

What happens when an electron jumps orbits?

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Answer

It either absorbs or emits energy.

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Question

What is the name of the most recent atomic model?

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Answer

The quantum model.

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Question

Name three scientists who contributed to the quantum model.

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Answer

Schrödinger, Heisenberg, and de Broglie.

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