AZ Chemistry

5 Chemistry Models of Atoms – Theory – Scientists – Definition

The concept of atom, especially the chemistry models of atoms, is really important in chemistry study. Atom is the tiniest of an element. Atom consists of three main parts which are proton, electron and neutron. Knowing the basic concept of proton, electron, neutron is helpful to understand the chemistry models of atoms. This article will cover the chemistry models of atoms. We will present you the development of atom models and the chemical reactions related to atom.

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Atom Basic Concept

As mentioned previously, atom consists of three main components: proton, neutron and electron. The structure of atom consists of nucleus and electrons. Nucleus is the center of an atom where the proton and neutron are located. Here’re brief explanations about atom components

Proton. Proton lies inside the nucleus. It has the positive charge. The numbers of protons in the atom is called atom number. In chemistry, proton number has the symbol of capital letter Z
Neutron. Just like proton, neutron is located in the nucleus. It has the neutral or zero charge. Neutron has the symbol of letter N. If we add numbers of protons and neutron, we’ll get the atomic mass.
Electron. Electron is the moving part in the atom. It orbits the nucleus. Differ from proton, electron has the negative charge. The mass of electron is really small compared to proton and neutron. It has mass of approximately 9.1095 x 10^-31 kg.

Also read: Proton, Electron, Neutron

1. Ancient Atom Theory

Democritus was the first person who discovered the theory of atom. He believed that there must he the piece of matter which is very small as it’s impossible to see. He described this particle as atomos or indivisible in Greek language. Based on his theory, atoms give the unique characteristic to the material which they form. Atoms have the different size and shape. They moved in constant speed in the void form. They did collided with each other. In this collisions, they stick together. The combination of atoms will change the characteristic of a matter.

2. Dalton Threory

Even though Democritus did the great theory of atom, he were not able to explained the chemical process in atom, especially the chemical models of atoms. There was no experiment conducted to support Democritus’s theory. After his theory, many scientist developed the research to understand the chemical process in an atom. In 1803, Dalton made the great atom theory. His theory has five basic principle as following points:

All mater contains very small particles which are called atoms. He belived that atoms has the small shape and solid spheres form. He also said that atoms have various motions
Atom can not be destructed and changed. The atoms in element can not be created, destroyed, divided or transformed. He used the Antoine Lavoisier theory to support this point
The weight of atom determines the characteristic of atom. Dalton believed that all atoms in the same element must have same weights. Every single atoms in oxygen is same to another. While atoms in the different element will have the different characteristic from one to another.
Atoms combine in the small and whole-all rations in chemical reactions. Based on Dalton’s experiment, he concluded that the chemical reactions will occur based on atom to atom ratios
Atoms may combine in more than one-all ratios in element reactions. There were multiples number ratios in various compounds like oxygen compound.

3. Modern Theory – Thompson & Rutherford

After the discovery of Dalton, the scientist were able to develop some great theories and experiments to help us understand the chemical models of atom. In 18977, J.J Thomson successfully discovered the electron part in the atom. He did the experiment using the cathode ray. He represented the cathode rays as the negative charge. Based on this experiment, he released the concept of atom model as the plum pudding. The raisins represented the negative charge electron while the dough represented the positive charge of atom.

After Thompson’s atomic theory, Ernest Rutherford, Thompson’s student, conducted the experiment which countered his teacher’s atomic theory. In 1911, he performed the experiment using the alpha particles. He shoot the alpha particle through the gold foil. This experiment resulted that most of the alpha particles passed through the gold foil. However, there were few alpha particles which are deflected back.

Rutherford believed that there were the positive charge nucleus. in the center of atom and negative charge electron around the nucleus. The nucleus finding by Rutherford is really helpful to understand the chemistry study, especially the chemical models of atom.

4. Bohr Theory

After Rutherford’s great theory, his student, Neils Bohr made the new atom model in 1913. His theory consists of some principles as follow:

Electrons are located in the certain orbits around the atom’s nucleus. These orbitals are stable. Bohr called these parts as the stationary orbits
Every orbit has the energy level. The differnt orbit will have the different level of energy. The orbit nereast the nucleus, as an example, will have the different energy level with the another orbit
There are energy transfer in electron’s move. Electron will absorb the energy when it moves form the lower orbit to higher orbit. In contrast, electron will emit the energy when it moves from higher orbit to lower orbit
The difference of orbit energy level determines the energy and frequency of light which is emitted or absorbed.

This theory inspired another scientist to complete this belief. Erwin Schrodinger successfully developed the theory of electron certain positions in the atom. His theory is popularly known as the atom quantum mechanical model. Differ from Bohr model, this theory was not able to determine the exact orbit of electron. Instead, this theory predicted the location of the electron. We will cover the detailed explanation about this part on the next section

5. Chadwick Theory

In 1932, James Chadwick completed the chemical models of atoms by finding out the neutral charge in the atom. He did the experiment by passing the alpha particles through the beryllium atoms. Based on his experiment, he discovered that there were the neutral electric charges in the nucleus part of atom. He named this part as the neutron. This experiment showed that the neutron had the same mass of the proton.

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Four Quantum Numbers

In chemistry models of atoms, we will learn about quantum numbers. They are the properties which explain the distribution of electrons in the atom. The four quantum numbers consist of following terms:

Principal Quantum Number (n). It’s the number which describe the electron’s main energy level. It’s also known as the electron shell. The principal quantum number always has the positive integer such as n= 1, 2, 3, 4, 5, and so on
Secondary Quantum Number (l). This numbers tell the energy sub-level of electron. We also know this as the type of electron orbitals. The numbers of secondary quantum depend on the principal quantum number. The maximum value of secondary quantum number is n-1. Secondary quantum number has another term of azimuthal or subsidiary.
Magnetic Quantum Number (ml). This term describes the amount of possible orientations for every orbital type. We know that secondary quantum number defines the electron orbital type, so the number of magnetic quantum will depend on the secondary quantum number. The value of ml has ranges between -l to +l. So, if l : 2, so the ml would be -2, -1, 0, 1, 2.
Spin Quantum Number (mS). This numbers represent the possible two orientations of an electron if there’s effect of magnetic field or another electron which is located on the same orbital. There’re only two electron which are able to occupy the same orbital. They should possess opposite spins. In this condition, we will have the pair of electrons. The value of spin quantum numbers are +1/2 and -1/2.

These four quantum numbers tell the electron’s arrangement in the atom. The numbers don’t explain the exact location of electron in the atom, but it’s more likely to be probability distributions and potential energy level of electrons. We can see the probability distributions by knowing the secondary quantum number (l) and magnetic quantum number (ml). While the main quantum number (n) dan secondary quantum number (l) will represent the potential energy level in atom’s orbital.

Chemical Bonding

The chemical models of atoms are strongly important to understand the chemical bonding in element. Electrons play the important role in the chemical reactions. Electron transfers from one atom to another atom occur in every chemistry reactions. Chemical reactions consist of two main chemical bondings which are ionic and covalent bonding. Here’re are the detailed explanations about these two bondings.

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1. Ionic Bonding

This bonding occurs in the elements which have the high different of electronegativity. This bonding will likely to happen between the metal and non-metal elements. To understand the electron transfer process, we can use the Lewis formula. This formula is the simple form of the electron transfers in the chemical reactions. In this bonding, electrostatic attraction is created between opposite charge ions. This attraction will form the strong ionic bonding. This is the thing which keeps the atom together.

2. Covalent Bonding

Differ from ionic bonding, covalent bonding is likely to occur in the element with similar amount of electronegativity. This bonding usually happens between the non-metal elements. The electron transfer in this reaction will never complete. As a result, the two atoms will share the electrons. There is no electrostatic attractions occurring in this bonding. The atoms keep together because of the octet rule fulfillment.