science about atoms and molecules

• Atoms are the smallest particles that can exist independently.
• Protons have a positive charge, neutrons have no charge, and electrons have a negative charge.
• The nucleus is made up of protons and neutrons, with electrons orbiting around it.
• Atoms are the smallest particles that can exist, while molecules consist of two or more atoms.
• Molecules are made up of two or more atoms bonded together.
• The nucleus is located at the center of an atom, containing protons and neutrons.
• Molecules are made up of two or more atoms chemically bonded together.
• The number of protons determines an atom's identity as an element.
• Compounds are formed when different elements combine chemically to form new substances.
• Elements cannot be broken down into simpler substances by chemical means.
• Electrons orbit around the nucleus in shells. there are 3 parts of sheels the K shell is the first shell that holds only 2 electrons, the L shell holds 8 electrons, the M 18 electrons, (N shell holds 32 electrons)
• Shells are energy levels where electrons can be found.
• Isotopes are different forms of the same element with varying numbers of neutrons.
• Molecules are formed when atoms bond together through chemical reactions.
• Each shell has a maximum number of electrons it can hold.
• Compounds are formed when elements chemically combine to form new substances.
• Properties of 'cathode' rays:

  1. they travel in straight lines
  2. they consist of material particals
  3. negetively charged particals
  4. they produce heating effects
  5. When the magnetic field is applied perpendicularly to the path of the rays they get deflected in the direction expected for negative particles
  6. they produce a greenish flourence by striking the glass walls
  7. they produce X-rays when they hit hard metals like :tungsten , molybdeum
  8. they have an penetraiting effect(the ability of an orbital to attract an electron.)
• the diagram for discovery of electons by JJ Thompson in 1897-