Stoichiometry- 4

• What are the symbols of the elements listed in Activity 1?

  Mg, Cl, Al, N, K, Ca, Li, F, O, Ne, H, S, Si
• What does the Group number indicate about an atom?

  It tells us how many electrons are in the outer shell.
• What do the group number and the number of electrons tell us about atoms?

  • They indicate how many electrons are needed for a full outer shell.
  • Group 1 has 1 outer electron, easy to lose 1.
  • Group 2 has 2 outer electrons, easy to lose 2.
  • Group 3 has 3 outer electrons, easy to lose 3.
  • Group 5 has 5 outer electrons, easy to gain 3.
  • Group 6 has 6 outer electrons, easy to gain 2.
  • Group 7 has 7 outer electrons, easy to gain 1.
• What is the valency of elements in Group 1?

  They can create 1 bond with 1 other atom (valency of 1).
• What is the valency of elements in Group 2?

  They can create 2 bonds with either 1 or 2 atoms (valency of 2).
• What is the valency of elements in Group 7?

  They can create 1 bond with 1 other atom (valency of 1).
• Why does Group 0 have a valency of 0?

  Because they have a full outer shell and do not need to bond with other atoms.
• In the reaction between calcium and chlorine, what is the valency of calcium?

  Calcium has a valency of 2.
• In the reaction between calcium and chlorine, what is the valency of chlorine?

  Chlorine has a valency of 1.
• How can we use the valencies of atoms to determine chemical formulas?

  • The valency indicates how many bonds an atom can form.
  • Example:
  • Hydrogen (valency of 1) + Oxygen (valency of 2) = H₂O
  • Magnesium (valency of 2) + Chlorine (valency of 1) = MgCl₂
  • Aluminium (valency of 3) + Oxygen (valency of 2) = Al₂O₃
• What is the formula for potassium chloride?

  KCl
• What is the formula for aluminium chloride?

  AlCl₃
• What is the formula for magnesium chloride?

  MgCl₂
• What is the formula for hydrogen fluoride?

  HF
• What is the formula for lithium chloride?

  LiCl
• What is the formula for sodium oxide?


  Na₂O
• What is the formula for potassium bromide?

  KBr
• What are the valencies and formulas of common ions to remember?

  • Sulphate: Valency -2, Formula SO₄
  • Ammonia: Valency 0, Formula NH₃
  • Nitrate: Valency -1, Formula NO₃
  • Carbonate: Valency -2, Formula CO₃
  • Ammonium: Valency +1, Formula NH₄
  • Hydroxide: Valency -1, Formula OH
• What is the formula for lithium hydroxide?

  LiOH
• What is the formula for sodium sulphate?

  Na₂SO₄
• What is the formula for magnesium carbonate?

  MgCO₃
• What is the formula for ammonium chloride?

  NH₄Cl
• What is the formula for aluminium nitrate?

  Al(NO₃)₃
• How do you determine the formula using diagrams?

  1. If a metal is present, it comes first.
  2. If no metal but Hydrogen is present, Hydrogen comes first.
  3. If no metal and no Hydrogen, the element from the lowest group comes first.
• What is the formula for a compound with Lithium and Chlorine?

  LiCl
• What is the formula for a compound with Hydrogen and Chlorine?

  HCl
• What is the formula for a compound with Carbon and Oxygen?


  CO₂
• What are the formulas of the compounds listed in the last section?

  1. LiCl
  2. HCl
  3. CO₂
• What are the symbols for the elements zinc, lead, sodium, chlorine, and iron?

  Zn, Pb, Na, Cl, Fe
• What is a compound?

  A compound is a substance formed when two or more elements are chemically bonded together.
• What is an element?

  An element is a pure substance that cannot be broken down into simpler substances by chemical means.
• Which of the following is a compound: A, B, or C?

  It depends on the specific definitions of A, B, and C provided in the context.
• How do you name compounds formed from a metal and a non-metal?

  • The metal name comes first.
  • The non-metal name follows, ending in ‘-ide’.
• What is the name of the compound formed from magnesium and oxygen?

  Magnesium oxide
• What is the name of the compound formed from sodium and chlorine?

  Sodium chloride
• What is the name of the compound formed from oxygen and iron?

  Iron oxide
• How do you name compounds that contain two elements plus oxygen?

  • The name ends in ‘-ate’.
  • Example: Iron + Sulphur + Oxygen → Iron sulphate.
• What is the name of the compound formed from calcium, carbon, and oxygen?

  Calcium carbonate
• What is the name of the compound formed from magnesium, nitrogen, and oxygen?

  Magnesium nitrate
• What is the naming convention for compounds containing more than two elements?

  • The ending of the other non-metal usually changes to ‘-ate’.
  • Example: Nickel sulphate.