Wave Motion, Atomic Structure, and Chemical Bonds

Posted on Dec 20, 2024 in Physics

Wave Motion and its Characteristics

The wave movement is a form of energy transmission that is not accompanied by the transport of matter. A wave is an undulatory movement, a propagation of vibrations, that is, the propagation of a periodic motion around the equilibrium position of a body. A wave takes the position that every moment that the perturbation produces. Waves are mechanical waves or materials that arise when a disturbance occurs in an elastic medium, without which there is no propagation. Electromagnetic waves, although they can be transmitted through certain media, do not necessarily require an elastic medium because the waves propagate in a vacuum. In longitudinal waves, the vibrations of particles around their equilibrium point occur in the same direction in which the wave propagates. The longitudinal waves are produced by compression and expansion between the particles that vibrate. In transverse waves, the vibrations of particles around their equilibrium point occur in the direction perpendicular to that of wave propagation. A wavefront or surface is the line formed by points to which the disturbance has come at one instant. The ray is the imaginary line perpendicular to the wavefront. The rate of spread, v, is the distance that the wave runs in each unit of time. The wavelength, ?, is the distance between two consecutive points of this wave that vibrate in the same way. It is expressed in meters. The period, T, is the time it takes for the disturbance to traverse the wavelength. It coincides with the time a point takes in making a complete vibration. It is expressed in seconds. The frequency, f, is the number of vibrations performed by a point in unit time. Its unit is the Hertz (Hz), which means “per second”. The wave amplitude, A, is the maximum separation that comes from the position of equilibrium points of each medium. It is measured in meters. The intensity, I, of a wave movement is the amount of energy flowing through the middle of the unit surface perpendicular to the propagation direction in unit time. It is equivalent to the power per unit area. It is expressed in W/m2.

Sound as a Mechanical Wave

The sound is a mechanical wave because it needs a material medium to propagate and it is a longitudinal wave because the particles of the medium oscillate in the same direction in which the wave spreads, casting sonic energy. It propagates in the same medium at a constant speed (v = 340m/s). Intensity is defined as the physical energy that passes through a second-drive surface placed perpendicular to the direction of propagation of sound. It allows us to distinguish the sounds of bass and treble, so it is frequency-dependent. The sounds of the same intensity and same tone can be distinguished by pitch. If the intensity is ten times higher, sonority increases by 10dB.

Light as an Electromagnetic Wave

Visible light consists of electromagnetic waves that can be detected with the sense of sight. Light waves, as well as other electromagnetic waves, do not need an elastic medium to propagate. Light spreads in a straight line. The reflection of light is the change of direction that a light ray undergoes when hitting the surface of bodies. Reflected light continues to spread itself by the same medium. Mirrors are flat, smooth, and polished surfaces capable of reflecting in the same direction a beam of parallel rays. Refraction of light is the change of direction when a luminous ray passes from one medium to another where it spreads at a different velocity. Visible light, infrared radiation, and ultraviolet are part of a broad spectrum of waves called the electromagnetic spectrum.

Atomic Theory

  • Matter is made up of indivisible atoms.
  • Atoms are unchanged.
  • Atoms of the same element are alike: they have the same mass and chemical properties.
  • Atoms of different elements have different masses and chemical properties.
  • Chemical compounds are formed by the combination of two or more atoms of different elements.
  • When two or more atoms of different elements combine to form the same compound, they do so in a simple ratio of integers.
  • In chemical reactions, atoms are neither created nor destroyed. Only their distribution in substances changes.

Modern Atomic Model

  • The atom is divisible because it contains subatomic particles.
  • Some of these particles are negatively charged.
  • The rest of the atom is the largest part of its mass and has a positive charge.
  • As the atom is electrically neutral, we must deduce that the number of negative charges is equal to the number of positive charges.
  • The atomic emission spectrum is the set of electromagnetic radiation emitted by the atom of a chemical element previously excited, either by using heat or electricity.

Bohr’s Atomic Model

  • The atom has a central nucleus where nearly all its mass is concentrated, provided by protons and neutrons.
  • The positive charges of protons are compensated by the negative charge of electrons outside the nucleus.
  • The electrons rotate at high speed around the nucleus and are separated from it by a distance.
  • There are a determined number of stable circular orbits along which the electron is traveling at high speed without releasing energy.
  • The electron is in each orbit, a certain energy that will increase as the orbit moves away from the nucleus. What characterizes an orbit is that it owns the energy level.
  • The electron radiates energy when it goes from a higher energy level to a lower one, emitting a definite amount of energy in the form of radiation.

Types of Chemical Bonds

Covalent Bonds

Simple Covalent Substances

Usually gaseous. Low melting and boiling points. Not conductive.

Molecular Substances

Gases, liquids, or solids, generally not soluble. Very low melting and boiling points. Not conductive.

Reticular Substances

Hard, high melting and boiling points, insoluble, and conductive.

Ionic Bonds

Solid at room temperature. High melting and boiling points. Hard, brittle, poor conductors in the solid-state, good conductors in liquid. Mostly soluble.

Metallic Bonds

Hard enough. Good thermal and electrical conductors. Shiny.