Electron Arrangement

• What is the focus of today's video?

  Arrangement of electrons in atoms
• Why do most atoms have an incomplete outer shell?

  They need a full outer shell to be stable
• What happens if an atom has an incomplete outer shell?

  It reacts with another atom
• What is the atomic number of sodium?

  11
• How many protons does sodium have?

  11 protons
• How are electrons arranged around the nucleus?

  In shells around the nucleus
• How many electrons can the first shell hold?

  2 electrons
• How many electrons can the second shell hold?

  8 electrons
• What is the best way to add electrons to the shells?

  In top, right, bottom, left positions
• What does it mean if an atom is unstable?

  It wants to react with another atom
• What do most atoms want to form?

  Molecules or compounds
• What is unique about noble gases?

  They have completely full outer shells
• What is the atomic number of argon?

  18
• How many electrons does argon have?

  18 electrons
• How would you write the electron structure of argon?

  2, 8, 8
• How many electrons does calcium have?

  20 electrons
• What is the electron structure of calcium?

  2, 8, 8, 2
• Why is calcium unstable?

  It has two electrons in its outer shell
• What happens when calcium loses two electrons?

  It becomes a calcium ion with a +2 charge
• How do we denote ions in diagrams?

  With square brackets and charge in the corner
• What is the atomic number of fluorine?

  9
• How many electrons does fluorine have?

  9 electrons
• What is the electron structure of fluorine?

  2, 7
• How does fluorine achieve stability?

  By gaining one more electron
• What charge does a fluoride ion have?

  -1 charge
• How is the electron structure of a fluoride ion written?

  2, 8
• What are the key points about electron arrangements in atoms?

  • Atoms need a full outer shell to be stable
  • Electrons are arranged in shells around the nucleus
  • First shell holds 2 electrons, second holds 8, third holds 8
  • Atoms react to achieve full outer shells
  • Noble gases have full outer shells and are stable
• How do you determine the electron arrangement for the first 20 elements?

  1. Identify the atomic number
  2. Draw the nucleus
  3. Fill the first shell with 2 electrons
  4. Fill the second shell with 8 electrons
  5. Fill the third shell with 8 electrons
  6. Write the structure as numbers (e.g., 2, 8, 8)
• What are the differences in stability between sodium, calcium, and fluorine?

  • Sodium: 1 electron in outer shell, unstable
  • Calcium: 2 electrons in outer shell, unstable
  • Fluorine: 7 electrons in outer shell, unstable
  • All want to react to achieve stability