chapter 5 chem ocr

• What is the main topic of section 5 in the study material?

  Electrons and bonding
• What is the maximum number of electrons in the first four shells?

  • Shell 1: 2 electrons
  • Shell 2: 8 electrons
  • Shell 3: 18 electrons
  • Shell 4: 32 electrons
• How are electrons arranged within an atom?

  Electrons are arranged in shells surrounding the nucleus.
• What is the principal quantum number *n*?

  *n* is the shell number or energy level number in an atom.
• What is wave-particle duality in relation to electrons?


  It is the concept that electrons exhibit properties of both waves and particles.
• What is the formula for the maximum number of electrons in a shell *n*?

  Number of electrons = $2n^2$
• How many electrons can the shell with *n* = 5 hold?

  50 electrons
• How many electrons can the shell with *n* = 6 hold?

  72 electrons
• How many electrons can the shell with *n* = 7 hold?

  98 electrons
• What are atomic orbitals?

  • Regions around the nucleus that can hold up to two electrons
  • Represented as areas with a high probability of finding an electron
  • Types include s-, p-, d-, and f-orbitals
• What shape does an s-orbital have?

  An s-orbital has a spherical shape.
• How many electrons can an s-orbital hold?

  An s-orbital can hold up to 2 electrons.
• How many p-orbitals are present in the second shell?

  There are three p-orbitals in the second shell.
• What is the shape of a p-orbital?

  A p-orbital has a dumb-bell shape.
• How many d-orbitals are present in the third shell?

  There are five d-orbitals in the third shell.
• How many f-orbitals are present in the fourth shell?

  There are seven f-orbitals in the fourth shell.
• What are the rules for filling orbitals?

  1. Orbitals fill in order of increasing energy.
  2. Electrons pair with opposite spins.
  3. Orbitals with the same energy are occupied singly first.
• In which order do the sub-shells fill in the n = 2 shell?


  The order of filling is 2s, then 2p.
• What is the significance of opposite spins in electron pairing?


  Opposite spins help to counteract the repulsion between the negative charges of the two electrons.
• What is the electron configuration of krypton (Z = 36)?

  1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶
• Why does the 4s sub-shell fill before the 3d sub-shell?

  Because the 4s sub-shell has a lower energy level than the 3d sub-shell.
• What is shorthand notation for electron configurations?

  • Expresses electron configurations in terms of the previous noble gas
  • Emphasizes similarities in outer shell electron configurations
  • Example: Li = [He]2s¹
• What is the definition of ionic bonding?

  Ionic bonding is the electrostatic attraction between positive and negative ions.
• What are common cations?

  • Metal ions (e.g., Na⁺, Ca²⁺, Al³⁺)
  • Ammonium ions (NH₄⁺)
• What are common anions?

  • Non-metal ions (e.g., Cl⁻, O²⁻)
  • Polyatomic ions (e.g., NO₃⁻, SO₄²⁻)
• How are ionic compounds formed?

  Ionic compounds are formed by the transfer of outer-shell electrons from a metal atom to a non-metal atom.
• What do dot-and-cross diagrams represent?

  Dot-and-cross diagrams represent the transfer of electrons in ionic bonding.
• In the example of potassium fluoride (KF), what ions are formed?

  A K⁺ ion and an F⁻ ion are formed.
• What is the electron configuration of calcium (Ca)?

  1s²2s²2p⁶3s²3p⁶4s²
• What is the electron configuration of oxygen (O)?

  1s²2s²2p⁴
• What happens to the electron configuration of calcium when it forms a Ca²⁺ ion?

  It loses two electrons from the 4s sub-shell.
• What happens to the electron configuration of oxygen when it forms an O²⁻ ion?

  It gains two electrons in the 3p sub-shell.
• What are the characteristics of d-block elements in terms of electron configuration?

  • The 4s sub-shell fills before the 3d sub-shell
  • The 4s sub-shell empties before the 3d sub-shell
• What is the electron configuration of nickel (Ni)?


  1s²2s²2p⁶3s²3p⁶3d⁸4s²
• What is the electron configuration of the Ni²⁺ ion?


  1s²2s²2p⁶3s²3p⁶3d⁸
• What is ionic bonding?

  • Electrostatic attraction between positive and negative ions
  • Holds together cations and anions in ionic compounds
• What are the common types of ions in ionic compounds?

  • Cations: metal ions and ammonium ions
  • Anions: non-metal ions and polyatomic ions
• How do dot-and-cross diagrams help in understanding ionic bonding?

  • Show the transfer of electrons
  • Help visualize the charge on each ion
  • Account for all electrons involved in bonding
• What is the significance of noble gas configurations in ionic bonding?

  • Ions formed often have outer shells with the same electron configuration as the nearest noble gas
  • This configuration leads to stability in ionic compounds
• What happens to outer-shell electrons during ionic bonding?


  Outer-shell electrons from a metal atom are transferred to the outer shell of a non-metal atom.