Grade 9 Chemistry Study Guide: Atomic Structure, Isotopic Abundance, Nitrogen, Magnesium Oxide, and Chlorine

Nitrogen Element: Properties, Biological Role, and Atomic Structure

Physical & Chemical Properties

• Physical State: Colorless, odorless, and tasteless gas.
• Atmospheric Abundance: Thermoset most plentiful element in the Earth's atmosphere.
• Industrial & Technical Uses:
  • Food processing applications.
  • Refrigeration systems.

Biological Vitality in Plants

• Chlorophyll Component: Essential major component of chlorophyll, enabling plants to absorb sunlight energy and perform photosynthesis to manufacture their own food using water ($\text{H}_2\text{O}$) and carbon dioxide ($\text{CO}_2$).
• Protein Synthesis: Essential component of amino acids, which serve as the fundamental building blocks of proteins.
• Consequence of Deficiency: Without proteins, plants wither and die.

Atomic Structure & Energy Level Distribution

• Visual Coding Key:
  • • represents an electron.
  • ◯ represents the nucleus.
• Electron Cloud Distribution:
  • Inner energy level ($K$ shell): $2\,\text{electrons}$
  • Outer energy level ($L$ shell): $5\,\text{electrons}$
  • Total number of electrons = $2 + 5 = 7\,\text{electrons}$

Exercise 3 Solved Solutions

• 1. Text Analysis Answers:
  • 1.1 Food Production Process: Photosynthesis.
  • 1.2 Physical Properties: Colorless gas and odorless gas (or tasteless gas).
  • 1.3 Effect of Lack of Protein: Plants wither and die.
• 2. Total Number of Electrons: $7\,\text{electrons}$.
• 3. Atomic Number ($Z$) Deduction:
  • In a neutral atom, the number of protons ($Z$) is equal to the total number of electrons.
  • $Z = 7$
• 4. Mass Number ($A$) Calculation:
  • Given: Nucleus contains $7$ uncharged particles (neutrons, $N = 7$).
  • Formula: $A = Z + N$
  • Calculation: $A = 7 + 7 = 14$
• 5. Relative Nuclear Charge Calculation:
  • Given: Relative charge of a proton $+e = 1+$
  • Formula: $Q_{\text{nucleus}} = Z \times (+1)$
  • Calculation: $Q_{\text{nucleus}} = 7 \times (+1) = 7+$ (or $+7e$)

Magnesium Oxide: Characteristics, Medical Applications, and Nuclear Constituents

Chemical & Physical Characteristics

• Historical Context: Oldest magnesium salt described in former medical dictionaries.
• Elementary Content: Contains $60.3\%$ elementary magnesium.
• Solubility: Poor assimilation due to low solubility.
• Physical Appearance & Names: White powder, commonly referred to as "chalk", magnesium oxide, or periclase.

Medical Importance & Applications

• Functions as an active ingredient in pharmaceutical products.
• Used to regulate magnesium levels in human bodies (found in medications such as Magnosol and Sympathyl).
• Used to fight and relieve stomach pain.

Nuclear Constituents (Document 1 Histograms)

• Proton Histogram Data:
  • Oxygen ($\text{O}$): $8\,\text{protons}$
  • Magnesium ($\text{Mg}$): $12\,\text{protons}$
• Neutron Histogram Data:
  • Oxygen ($\text{O}$): $8\,\text{neutrons}$
  • Magnesium ($\text{Mg}$): $12\,\text{neutrons}$

Exercise 4 Solved Solutions

• 1.1 Completed Table of Atomic & Mass Numbers:

• 1.2 Atomic Representation (${}_{Z}^{A}\text{X}$):
  • Oxygen: ${}_{8}^{16}\text{O}$
  • Magnesium: ${}_{12}^{24}\text{Mg}$
• 1.3 Nuclear Charge of Magnesium:
  • Given elementary charge $e = +1$
  • Formula: $Q_{\text{nucleus}} = Z \times (+1)$
  • Calculation: $Q_{\text{nucleus}} = 12 \times (+1) = +12$ (or $12+$)
• 1.4 Number of Electrons:
  • Since both are neutral atoms, number of electrons = number of protons ($Z$).
  • Oxygen: $8\,\text{electrons}$
  • Magnesium: $12\,\text{electrons}$
• 2. Medical Importance Summary (from text):
  • Active ingredient in pharmaceuticals.
  • Regulates internal magnesium levels (e.g., Magnosol, Sympathyl).
  • Relieves stomach pain.

Fundamentals of Atomic Representation and Composition

Summary Data (Grade 9 Sheet 2 - Document 1)

Exercise 1 Solved Solutions

• 1. Symbolic Representation of Oxygen:
  • Format: ${}_{Z}^{A}\text{O}$
  • Representation: ${}_{8}^{16}\text{O}$
• 2. Neutron Count of Sodium ($\text{Na}$):
  • Formula: $N = A - Z$
  • Calculation: $N = 23 - 11 = 12\,\text{neutrons}$
• 3. Complete Composition of Magnesium Atom ($\text{Mg}$):
  • Protons ($Z$): $12$
  • Electrons: $12$ (neutral atom)
  • Neutrons ($N$): $A - Z = 24 - 12 = 12\,\text{neutrons}$
• 4. Analysis of Chlorine Atom Nucleus and Cloud:
  • Given: Relative nuclear charge $Q_{\text{nucleus}} = 17+$, elementary charge $+e = 1+$
  • 4.1 Atomic Number ($Z$):
    • $Q_{\text{nucleus}} = Z \times (+1) \implies 17+ = Z \times (+1) \implies Z = 17$
  • 4.2 Relative Charge of Electron Cloud:
    • Since an atom is electrically neutral overall ($Q_{\text{atom}} = 0$), the electron cloud charge is equal in magnitude and opposite in sign to the nuclear charge.
    • $Q_{\text{cloud}} = -Q_{\text{nucleus}} = 17-$
  • 4.3 Number of Electrons:
    • Total electrons = $17$

Chlorine Element: Disinfection Applications and Isotopic Mixture

Chemical Behavior & Applications

• Disinfectant Nature: Chlorine gas is a disinfectant chemical that reacts with water to generate nascent oxygen, which effectively kills bacteria.
• Applications:
  • Purification and treatment of drinking water.
  • Sanitation of swimming pools (added in strictly limited amounts).
  • Production of household bleach.
• Natural Existence: Naturally occurs as an isotopic mixture.

Isotopic Abundance Data (Document 1)

• Pie Chart Values:
  • ${}_{17}^{37}\text{Cl}$ abundance = $25\%$
  • ${}_{17}^{35}\text{Cl}$ abundance = $X\,\%$

Exercise 2 Solved Solutions

• 1.1 Designation of Associated Numbers (35 and 17):
  • 35: Represents the Mass Number ($A$), which is the total number of nucleons (protons + neutrons) in the nucleus.
  • 17: Represents the Atomic Number ($Z$), which is the total number of protons in the nucleus.
• 1.2 Calculation of Relative Percentage Abundance ($X\,\%$):
  • Total natural isotopic abundance = $100\%$
  • Calculation: $X\,\% = 100\% - 25\% = 75\%$
• 2. Complete Isotope Data Table:

• 3. Isotope Definition Proof:
  • ${}_{17}^{35}\text{Cl}$ and ${}_{17}^{37}\text{Cl}$ are isotopes because they belong to the same chemical element (Chlorine) and have the same atomic number ($Z = 17$ protons), but different mass numbers ($A = 35$ and $A = 37$) due to differing numbers of neutrons ($18$ vs $20$ neutrons).
• 4. Identification of Heaviest Isotope:
  • ${}_{17}^{37}\text{Cl}$ is the heaviest isotope because it possesses a greater mass number ($A = 37$) compared to ${}_{17}^{35}\text{Cl}$ ($A = 35$).
• 5. Identification and Justification of Most Abundant Isotope:
  • Correct Choice: a) ${}_{17}^{35}\text{Cl}$
  • Justification: Its calculated relative percentage abundance is $75\%$, which is significantly higher than that of ${}_{17}^{37}\text{Cl}$ ($25\%$).
• 6. Purpose of Chlorine Gas in Swimming Pools:
  • It is added to swimming pools as a disinfectant chemical because it reacts with water to produce nascent oxygen, which destroys and kills bacteria to ensure water safety.