Case Based Question - 2 of Elements and Compounds

 

Passage 11

A molecule is the smallest unit of a compound that retains its chemical properties. For example, a single molecule of carbon dioxide (CO₂) contains one carbon atom bonded to two oxygen atoms. Molecules are held together by chemical bonds that determine the compound’s stability and structure.

  1. What is a molecule?
  2. How many atoms are in a single molecule of CO₂?
  3. Why are molecules important in chemistry?
  4. What type of bonds hold atoms together in a molecule?
  5. What happens to a compound’s properties if its molecular structure changes?

Passage 12

Ionic compounds are formed by the transfer of electrons between atoms, resulting in a positive and a negative ion. For example, when sodium (Na) donates an electron to chlorine (Cl), it forms sodium chloride (NaCl), a stable ionic compound. Ionic compounds are often soluble in water and have high melting and boiling points.

  1. How are ionic compounds formed?
  2. What type of ions does sodium become after donating an electron?
  3. Why is sodium chloride considered stable?
  4. Name a property of ionic compounds.
  5. What happens when an ionic compound dissolves in water?

Passage 13

Covalent compounds are formed when atoms share electrons. An example of a covalent compound is water (H₂O), where hydrogen and oxygen atoms share electrons to achieve stability. Covalent compounds generally have lower melting and boiling points compared to ionic compounds and can exist as gases, liquids, or solids at room temperature.

  1. How are covalent compounds formed?
  2. What type of bond exists in a water molecule?
  3. How does the melting point of covalent compounds compare to ionic compounds?
  4. Give an example of a covalent compound.
  5. In what states can covalent compounds exist at room temperature?

Passage 14

The law of conservation of mass states that in a chemical reaction, the total mass of the reactants equals the total mass of the products. For example, when hydrogen gas reacts with oxygen gas to form water, the mass of water produced equals the combined mass of hydrogen and oxygen.

  1. What does the law of conservation of mass state?
  2. How does this law apply to a reaction between hydrogen and oxygen?
  3. Why is it important to balance chemical equations?
  4. Can mass be created or destroyed in a chemical reaction?
  5. What is conserved in a chemical reaction according to this law?

Passage 15

An alloy is a mixture of metals or a metal with a non-metal to enhance its properties. For instance, steel is an alloy of iron and carbon, which makes it stronger and more durable than pure iron. Alloys are commonly used in construction, transportation, and electronics due to their desirable properties.

  1. What is an alloy?
  2. Give an example of an alloy and its components.
  3. Why is steel stronger than pure iron?
  4. Name two uses of alloys.
  5. How does adding carbon affect iron in making steel?

Passage 16

Some elements, such as oxygen and nitrogen, exist as diatomic molecules, meaning they are found naturally in pairs (O₂ and N₂). This pairing provides stability to these molecules and affects how they interact with other substances in chemical reactions.

  1. What does "diatomic" mean?
  2. Give two examples of diatomic molecules.
  3. Why do oxygen and nitrogen exist as diatomic molecules?
  4. How does being diatomic affect an element's stability?
  5. What is the molecular formula of nitrogen gas?

Passage 17

Periodic trends, such as electronegativity, ionization energy, and atomic radius, help predict how elements will react. Electronegativity is the tendency of an atom to attract electrons. For instance, fluorine has high electronegativity, meaning it readily attracts electrons to form bonds.

  1. What is electronegativity?
  2. Why is fluorine highly electronegative?
  3. What is a periodic trend?
  4. How does electronegativity affect bonding?
  5. Name another periodic trend besides electronegativity.

Passage 18

Hydrocarbons are organic compounds made solely of hydrogen and carbon atoms. Methane (CH₄), ethane (C₂H₆), and propane (C₃H₈) are common hydrocarbons. They are often used as fuels due to their ability to release energy when burned.

  1. What are hydrocarbons?
  2. Give an example of a hydrocarbon.
  3. Why are hydrocarbons commonly used as fuels?
  4. What elements make up hydrocarbons?
  5. How does the structure of methane differ from that of propane?

Passage 19

Isotopes are atoms of the same element with different numbers of neutrons. For example, carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. While they have the same atomic number, their differing mass numbers give them unique properties.

  1. What are isotopes?
  2. Name the three isotopes of carbon.
  3. How do isotopes differ within the same element?
  4. Why do isotopes have different mass numbers?
  5. Does the atomic number change in isotopes?

Passage 20

Noble gases, such as helium, neon, and argon, are elements in group 18 of the periodic table. They are inert, meaning they rarely react with other elements due to their full outer electron shells. This property makes them useful in applications like lighting and welding.

  1. What are noble gases?
  2. Give two examples of noble gases.
  3. Why are noble gases considered inert?
  4. In what group of the periodic table are noble gases found?
  5. Name one application of noble gases.


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