A photon is a fundamental particle of light and all other forms of electromagnetic radiation. It is the quantum or discrete unit of electromagnetic energy. Photons are unique in several ways:

Key Characteristics of a Photon:

1. Energy: Photons carry energy, which is directly proportional to the frequency of the radiation. The higher the frequency, the more energy a photon has. The energy $EE$ of a photon is given by the equation:

   $E=h\cdot f$where:

   • $EE$ is the energy of the photon,
   • $hh$ is Planck’s constant ($6.626\times 10^{-34}6.626\; \backslash times\; 10^\{-34\}$Joule-seconds),
   • $ff$ is the frequency of the radiation.
2. Massless: Photons have no rest mass, meaning they do not have mass when at rest. They always travel at the speed of light in a vacuum ($c=3\times 10^{8}c\; =\; 3\; \backslash times\; 10^8$meters per second).
3. Wave-Particle Duality: Photons exhibit both particle-like and wave-like properties, a concept known as wave-particle duality. As waves, photons exhibit characteristics such as interference and diffraction; as particles, they can be thought of as discrete packets of energy.
4. Speed: Photons always travel at the speed of light in a vacuum, regardless of their energy or frequency.
5. No Electric Charge: Photons have no electric charge, meaning they do not interact with electric fields in the same way charged particles do.
6. Interaction with Matter: Photons can interact with matter, for example, when they are absorbed or emitted by atoms during processes such as photoelectric effect (where electrons are ejected from a material when exposed to light) or stimulated emission (which forms the basis for lasers).

Examples of Photon Sources:

• Sunlight: The Sun emits photons, which are responsible for the visible light we see.
• Radio waves, X-rays, and Gamma rays: These are also forms of electromagnetic radiation, but with different photon energies and wavelengths.

Photons are the basic units of light and electromagnetic radiation, exhibiting both particle and wave properties, and they play a crucial role in a wide range of physical phenomena.

The periodic table is a tabular arrangement of chemical elements, organized based on their atomic number, electron configurations, and recurring chemical properties. The table provides a systematic way of understanding the relationships between different elements and predicting their behavior in chemical reactions.

Key Features of the Periodic Table

1. Rows (Periods): Horizontal rows of elements that show periodic trends in properties such as atomic size and ionization energy.
2. Columns (Groups or Families): Vertical columns containing elements with similar chemical properties. Elements in the same group typically have the same number of valence electrons.
3. Blocks: The table is often divided into blocks (s, p, d, f) based on the electron configuration of the elements.
4. Element Information: Each element is represented by its symbol, atomic number, and atomic mass.

Creator of the Periodic Table

The periodic table was created by Russian chemist Dmitri Mendeleev in 1869. Mendeleev arranged the elements in order of increasing atomic mass and noticed that their chemical properties repeated at regular intervals. This pattern, known as the periodic law, allowed Mendeleev to predict the properties of elements that had not yet been discovered at that time.

Later, the periodic table was refined by arranging elements according to their atomic number (instead of atomic mass), as proposed by Henry Moseley in 1913, leading to the modern version of the periodic table we use today.

Mendeleev’s work was groundbreaking because it provided a clear and predictive system for understanding the relationships between elements, which significantly advanced the field of chemistry.