Quantum - Teory Atom & Mekanika Kuantum (KIMIA)

Atomic model ERNEST RUTHERFORD (1871-1937) in 1911 which stated that the atom consists of a small positively charged nucleus (where the concentration of the entire mass of the atom) and is surrounded by electrons on their surface. However, this theory can not explain the stability of atoms. As they toured the protons, electrons experience a centripetal acceleration due to the effect of centripetal force (Coulomb force).

According to Maxwell's theory of classical mechanics, which states that moving charged particles will radiate energy. Then by Maxwell when electrons move around the nucleus will also radiate energy.

Transmitting this energy causes the electrons lose energy, so that the spiral-shaped trajectory radius is smaller, the slower the rate of electrons and eventually be attracted to the nucleus of the atom. If this is the case then the atoms will disappear, but in fact a stable atom.

In 1913, Niels Bohr use quantum theory to explain the spectrum of elements. Based on observations, the elements can emit a line spectrum and each element has a characteristic spectrum. According to Bohr,

Line shows the spectrum of electrons in an atom can only circulate on the trajectories with a certain energy level. In the electron trajectory can be circulated without signaling or energy absorption. Therefore, the electron energy so that the trajectory remains unchanged.
Electrons can move from one track to another track with emission or absorption of an amount of energy equal to the difference of the cost of energy levels.

ΔE = Ef - Ei
Description:

ΔE = energy accompanying the electron transfer

Ef = final energy level

Ei = the initial energy level


But Bohr's theory has drawbacks, namely:

Bohr could only explain the spectra of hydrogen gas, can not explain the spectrum of elements that the number of electrons is more than one.
Can not explain the presence of fine lines in the spectrum of hydrogen gas.


The weakness of the Bohr model of the atom can be explained by VICTOR LOUIS DE BROGLIE in 1924 with the theory of wave particle duality. According to de Broglie, in certain circumstances, the material moves have wave characteristics.

h
λ = -----
m. ν
where:

λ = wavelength (m)

m = mass of particle (kg)

ν = velocity (ms-1)

h = Planck's constant (Js 6,626.10-34)

The hypothesis proved correct with the discovery of the wave nature of electrons. Electron diffraction has properties, then the trajectory of the electron Bohr proposed is not justified. Wave does not move through a line, but rather spread in certain areas.


In 1927, Werner Heisenberg proposed that the position or location of an electron in an atom can not be determined with certainty. Heisenberg tried to determine the properties of subatomic and variables used to determine the nature of the atom. This is the nature of the particle position (x) and momentum (p).

The conclusion of the hypothesis is that there is always a subatomic measurement uncertainty and is defined as the product of the uncertainty of the position (Δx) the uncertainty of momentum (Δp) and formulated as follows:

h
Δx. Δp = ------
2π
Possibility (probability) of finding the electron at a given point at a certain distance from the point referred to as the Heisenberg Uncertainty Principle. This means that the movement of electrons along the track position can not be known precisely.


ATOM MODEL OF WAVE MECHANICS
Louis de Broglie hypothesis and Heisenberg's uncertainty principle is the basis of the model of Quantum Mechanics (Wave) proposed by Erwin Schrödinger in 1927, which proposed the concept to express the position of the electron orbitals in atoms. Orbital declare an area where electrons are most likely (the greatest opportunity) to be found.

Schrodinger agree with Heisenberg that the position of the electrons in an atom can not be determined with certainty, but that can be determined is the probability of finding the electron at a given point at a certain distance from the core. The room that has the greatest probability of finding an electron is called Orbital.

In quantum mechanics, atomic orbital model described resembles the "cloud". Some orbitals combine to form a group called the subshell.

Wave equation (Ψ = psi) of Erwin Schrodinger wave produces three numbers (quantum numbers) to declare the position (energy level, shape, and orientation) of an orbital, namely: the principal quantum number (n), the azimuthal quantum number (l) and the number quantum magnetic (m)

0.000000 0.000000
Stored in Class XI Chemistry, Materials Chemistry

ELECTRON CONFIGURATION CONNECTION WITH PERIODIC SYSTEM ELEMENTS

The electron configuration of the distribution of electron states in atoms. The atomic number indicates the number of electrons. This proves that there is a relationship between the properties of elements with electron configuration, katena Periodic Table of the Elements System (SPU) prepared by the increase in atomic number elements. At SPU Group known terms (vertical columns) and Periods (horizontal lines)

1. The Group

SPU is divided into 8 groups. Each class is divided into First Class (A) and Transition Group (B). The numbering is done based group owned by the valence electrons of an element. Each element has the same valence electrons will occupy the same group also

Based on the location of the last electron orbital, the electron configuration of elements in the SPU is divided into 4 blocks, namely blocks s, p block, d-block and f-block.

If the electron configuration ends in s or p block then surely occupy a class A
If the electron configuration ends in D block of class B then surely occupy
If the electron configuration ends in block f then surely occupy group B (Lanthanides, and Actinides n = 6, n = 7 (gol.radioatif))
In addition to determining the number of classes, determined by knowing the number of valence electrons in the final configuration.

Example:

1s2 2s2 2p6 11Na = 3S1

It can be seen that the last electron in the n = 3 has 1 valence electron, meaning class I and ending in s subshell, meaning Class A, so if combined into Class IA

2. Period

SPU consists of 7 periods. Periods prepared on the rise in the number of atoms. The elements that have the same amount of skin will occupy the same row. Thus the amount equal to the period of the skin, so that the period 1 has n-1, period 2 has n = 2, and so on.

Example:

1s2 2s2 2p6 11Na = 3S1

It can be seen that the last electron is at n = 3 which means that it has entered in Period 3

0.000000 0.000000
Stored in Class XI Chemistry, Materials Chemistry

ELECTRON CONFIGURATION BASED ON THE CONCEPT OF QUANTUM NUMBERS

Describe the arrangement of electron configuration / arrangement of electrons in atoms. In determining the electron configuration of an atom, there are three rules that should be used, namely: Rule Aufbau, Pauli rule, and Hund's Rule.

1. Rule Aufbau

Orbitals are starting from a low energy level to a higher energy level. Electrons have a tendency to occupy the subshell first low energy. The magnitude of the energy level of a subshell can be seen from the principal quantum number (n) and azimuthal quantum number (l) of the orbitals. Orbital priced (n + l) has a greater level of greater energy. If the price of (n + l) is the same, then the price of n-orbital is larger has a greater energy level. The order from lowest energy to highest as digaram made by Moeler Mnemonics are as follows:

1s <2s <2p <3s <3p <4s <3d <4p <5s <4d <5p <6s <4f <5d ....



DIAGRAM mnemonic MOOLER


2. Rules Pauli (Pauli exclusion)

This rule proposed by Wolfgang Pauli in 1926. Which states "there should not be two electrons in an atom with the same four quantum numbers". Will have the same orbital quantum number n, l, m, which is the same but the only difference being the spin quantum number (s). Thus, each orbital can contain only 2 electrons with spin (direction of turn) the opposite. Thus, the orbital can be occupied by a maximum of two electrons, because if the third electron is inserted it will have the same spin as the electron previous one.

Example:

On the 1s orbital, will be occupied by two electrons, namely:

First electron à n = 1, l = 0, m = 0, s = + ½

Both electron à n = 1, l = 0, m = 0, s = - ½

(This proves that even though the two electrons have n, l and m are the same but have different spin)



3. Rules Hund

This rule stated by Friedrick Hund 1930. Stating "the electrons in the orbitals of a subshell tend to unpaired".

New pairs of electrons in a subshell if it is no longer empty orbitals.

To express the distribution of electrons in the orbitals in a subshell, electron configuration is written in the form of orbital diagram.

An orbital is described in the form of a box, while the electrons occupy orbitals depicted with two arrows in opposite directions. If orn = bital contains only one electron, then the written arrows pointing up.

In applying the rules hund, then we have to write over the direction of the arrow to advance on all the boxes, and then followed by the direction of the arrow down if masihterdapat electron rest.