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• Monoatomic: A substance made of single atoms (e.g., noble gases like He, Ne)
• Diatomic: Molecules made of two atoms covalently bonded (e.g., O₂, H₂, Cl₂)
• Interatomic Forces: Forces between the nucleus and its own electrons
• Intermolecular Forces: Forces between separate atoms or molecules
• Atomic radius: distance from the nucleus to the outermost electron shell. </aside>

atomic structure:

• Protons and neutrons are located in the nucleus, which is positively charged.

• Electrons orbit the nucleus in shells, and there is a lot of space between the nucleus and the electrons.

• Formula for max electrons in a shell: 2n², where n is the shell number. (e.g., 1st shell = 2(1²) = 2)

• Atoms are the basic building blocks of matter. They have no overall electrical charge because:

• Number of protons = Number of electrons

electron configuration:

• Atomic Number = Number of protons
• Mass Number = Number of protons + neutrons (goes on top of the element)
• Number of electrons = Number of protons (goes below the element)

Electrons are arranged in shells (energy levels) around the nucleus.

• 1st shell: up to 2 electrons
• 2nd shell: up to 8 electrons
• 3rd shell: up to 8 electrons (GCSE level)
• There is no fixed limit to the number of shells

Example:

Oxygen (atomic number 8)

Electron configuration: 2, 6

ions:

• The valence electrons are those that are in the outmost shell of an atom or ion

• Based on the group number

  • Group 1- Hydrogen has 1 valence electron
  • Group 3- Boron has 3 valance electrons
  • The valency of transition metals is subject to the reaction/compound they form.

• Ion = an atom or group of atoms with a charge (positive = cation, negative = anion)

• Examples:

  • OH⁻ = hydroxide
  • NH₄⁺ = ammonium
  • NaCl: Na⁺ and Cl⁻

• Valency is the idea that defines the ability an atom has to complete its outermost octet. It refers to the outermost shell and the electrons in the outermost shells are valence electrons

• For example oxygen has 8 protons and 8 electrons in its neutral state, so when organised into an electron structure. There would be 2 electrons in the oxygen’s first shell and 6 in its last shell or valence shell. This means that Oxygen has a valency of 2 electrons as is oxygen has 8 electrons then their octet would be complete

• Valency is an atom’s ability to bond, usually equal to the number of electrons lost, gained, or shared.

• It is determined by the group number in the periodic table.

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Atoms form ions to become stable, usually to achieve a full outer electron shell

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isotopes:

Isotopes are atoms of the same element that have:

• The same atomic number
• The same number of protons
• Different mass numbers
• Different number of neutrons

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Isotopes behave the same chemically but may have different physical properties due to different masses.

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