Atomic Structure and Chemical Laws: A Comprehensive Summary
Lavoisier: Conservation of Mass
In any chemical reaction, the total mass of reactants is equal to the mass of the products. For example, 5g + 1.2g = 3.7g.
Proust: Definite Proportions
The proportion among the masses in which two or more elements combine to form a certain compound is always constant and independent of the procedure used to form it.
Dalton: Multiple Proportions
When two elements combine together to form more than one compound, the masses of one of them that combine with the same mass of the other to give various compounds are in a simple integer ratio.
Differences Between Thomson and Rutherford
Thomson stated that the atom should not be considered an indivisible particle, but rather that it must be formed by negative charges (electrons) that were embedded in a spherical mass of uniform density, charge, and a nature known as positive. Rutherford, on the other hand, proposed that the atom is composed of a crust and a core, and that it is almost empty. Electrons are located in the crust, orbiting the proton individually. Judgments: “The electrons should end up colliding with the nucleus. Electrons pass through all possible orbits.”
Bohr
Electrons only occupy certain positions around the nucleus with a determined energy. Each orbit of the atom corresponds to an energy level. The allowed energy levels are those in which angular momentum is a multiple of a constant. Energy is only absorbed or emitted when the electron transitions from one level to another. Failures: It did not explain why atomic orbits are quantized or why some properties of the elements are repeated periodically.
How Were Electrons and Protons Discovered?
Electrons – Thomson: In a vacuum discharge tube with a small amount of gas, cathode rays passed through a point from the cathode. These rays were diverted to the positive plate by applying an external electric field.
Protons – Rutherford: A substance emitting radioactive rays was placed within a lead shield. The beam was made to pass through a point and strike a 0.5 µm thick gold layer surrounded by a fluorescent zinc sulfide screen. A small amount was reflected, another was diverted, but most did not deviate. This suggested the existence of another positively charged subatomic particle: the proton.
Atomic Number
Indicates the number of protons in the nucleus and determines the element in question (Z).
Mass Number
Indicates the number of neutrons and protons, which form the core and determine the isotope of the element.
Significance of Quantum Numbers
- Principal (n): Represents the energy level.
- Orbital Angular Momentum (l): Determines the shape of the orbital and the energy within each level.
- Magnetic (m): Describes the orbital orientation in space and explains the splitting of spectral lines when an external magnetic field is applied.
- Magnetic Electron Spin: Gives us the value of an intrinsic property of electrons and other elementary particles.
Orbit
Electrons move in circular orbits around the nucleus.
Orbital
A region or volume of space within the atom where the probability of finding an electron with a specific energy is very high.
Electron Affinity
The energy change that occurs when an electron is added to a neutral atom of an element in the gas phase to form a negative ion in the gas phase (A + e- → A-). The greater the electron affinity, the greater the tendency to become an anion.
Atomic Radius
The atomic radius has no defined limits, so we cannot speak of its volume.
Ionization Energy
The energy required to be applied to a neutral atom of an element in the gaseous state to remove its outermost electron and form a monopositive ion in the gas phase.
Lattice Energy
Ionic compounds are very stable. The crystal structures formed during crystal formation release a large amount of energy. Lattice energy is the energy exchanged in the formation of one mole of an ionic crystal from the corresponding positive and negative ions in the gaseous state. The smaller (more negative) the lattice energy, the greater the stability of the ionic compound.