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Questions and Answers

What is the molecular formula of a water molecule?

  • H2O2
  • H2O (correct)
  • O2H
  • HO2

    • Which of the following best describes a tetratomic molecule?

  • A molecule consisting of eight atoms
  • A molecule consisting of four atoms (correct)
  • A molecule consisting of five atoms
  • A molecule consisting of two atoms

    • How many protons and neutrons are present in the oxygen isotope denoted as 168 O?

  • 8 protons, 10 neutrons
  • 7 protons, 10 neutrons
  • 8 protons, 9 neutrons
  • 8 protons, 8 neutrons (correct)

    • Which molecule consists of eight atoms?

    <p>Sulfur (S8)</p> Signup and view all the answers

    What does the atomic number (Z) indicate about an element?

    <p>It differentiates one element from another based on proton count.</p> Signup and view all the answers

    Which statement correctly describes isotopes?

    <p>Isotopes have the same atomic number but different mass numbers.</p> Signup and view all the answers

    What are polyatomic molecules typically composed of?

    <p>More than three or four atoms</p> Signup and view all the answers

    What is the molecular formula for a molecule of ammonia?

    <p>NH3</p> Signup and view all the answers

    What is the average atomic mass of chlorine if it is made up of isotopes 17 Cl and 37 Cl in a ratio of 3:1?

    <p>35.5 amu</p> Signup and view all the answers

    Which of the following is a known form of carbon that has 60 atoms?

    <p>Buckminsterfullerene</p> Signup and view all the answers

    Why do different isotopes of the same element have different atomic masses?

    <p>They contain different numbers of neutrons.</p> Signup and view all the answers

    What does the atomic mass of an element represent?

    <p>The average mass of all isotopes based on their abundance.</p> Signup and view all the answers

    What type of molecule is ethyl alcohol?

    <p>Polyatomic</p> Signup and view all the answers

    How many hydrogen atoms are present in one molecule of ethyl alcohol?

    <p>5</p> Signup and view all the answers

    In a neutral atom, how is the number of electrons related to protons?

    <p>Electrons equal the number of protons.</p> Signup and view all the answers

    What would happen if an oxygen atom had 9 neutrons and 8 protons?

    <p>It remains an isotope of oxygen.</p> Signup and view all the answers

    What charge does the calcium ion have in calcium phosphate?

    <p>+2</p> Signup and view all the answers

    Which of the following represents the correct formula for magnesium oxide?

    <p>MgO</p> Signup and view all the answers

    Based on the charge balance, how does one write the formula for sodium sulfate?

    <p>Na2SO4</p> Signup and view all the answers

    What is the expected compound formed between nitrogen and hydrogen?

    <p>NH3</p> Signup and view all the answers

    What is the net charge of the sulfate ion?

    <p>-2</p> Signup and view all the answers

    What compound do potassium and iodide ions form?

    <p>KI</p> Signup and view all the answers

    The formula for aluminium chloride is derived from which charges?

    <p>+3, -1</p> Signup and view all the answers

    What is the definition of a mole in chemistry?

    <p>A mole is the amount of substance that contains as many elementary entities as there are in 12 grams of Carbon-12.</p> Signup and view all the answers

    What is the primary reason for practicing the writing of compound formulas?

    <p>It improves understanding of ionic charges and compound formation.</p> Signup and view all the answers

    Why is the mole considered a convenient unit in chemistry?

    <p>It provides a standardized method for counting atoms and molecules.</p> Signup and view all the answers

    What does the term 'chemical equation' represent?

    <p>It represents the reaction between substances to form new products.</p> Signup and view all the answers

    What is the significance of the Latin word 'moles' in the context of the mole?

    <p>It means a 'heap' or 'pile', representing the concept of counting.</p> Signup and view all the answers

    When hydrogen and oxygen react, what is produced?

    <p>Water</p> Signup and view all the answers

    Which of the following represents a correct use of the mole concept?

    <p>A mole of water contains the same number of molecules as a mole of carbon dioxide.</p> Signup and view all the answers

    In the reaction 2H2 + O2 → 2H2O, how many hydrogen atoms are involved?

    <p>4</p> Signup and view all the answers

    Which of the following compounds has the molecular mass closest to H2O?

    <p>CH3OH</p> Signup and view all the answers

    What is the formula of the compound formed between Hg2+ and Cl–?

    <p>Hg2Cl2</p> Signup and view all the answers

    Which of the following is the correct formula for the compound formed between Pb2+ and PO4–?

    <p>Pb3(PO4)2</p> Signup and view all the answers

    What is the resulting formula when Ba2+ bonds with SO4–?

    <p>BaSO4</p> Signup and view all the answers

    What principle states that a pure substance consists of the same elements combined in the same proportion by mass?

    <p>Law of Definite Proportions</p> Signup and view all the answers

    According to the law of multiple proportions, what is true about the masses of elements that combine?

    <p>They are always in a ratio of simple whole numbers.</p> Signup and view all the answers

    What term describes the smallest particle of an element that exhibits all properties of that element?

    <p>Atom</p> Signup and view all the answers

    What is the value of Avogadro's number?

    <p>6.02 × 10^23</p> Signup and view all the answers

    What is referred to as the molar mass of a substance?

    <p>The mass of one mole of particles of the substance</p> Signup and view all the answers

    Study Notes

    Atomic Structure

    • Symbol representation like (^{12}_{6}C) indicates a total of 12 nucleons in carbon, with 6 protons and 6 neutrons.
    • (^{16}_{8}O) contains 8 protons and 8 neutrons, demonstrating the relationship between atomic number and nucleon count.
    • Atoms of an element have the same atomic number but can differ in neutron count, leading to different isotopes.
    • Example isotopes of oxygen: (^{16}O) (8 protons, 8 neutrons), (^{17}O) (8 protons, 9 neutrons), (^{18}O) (8 protons, 10 neutrons).

    Isotopes and Atomic Mass

    • Isotopes are defined as atoms with the same atomic number but different mass numbers.
    • Average atomic masses are calculated based on the abundance of isotopes.
    • Chlorine consists of isotopes (^{35}Cl) and (^{37}Cl) in a 3:1 ratio, which can be used to calculate its average atomic mass.

    Molecules and Compounds

    • Molecules can be diatomic or comprised of larger numbers of atoms.
    • Familiar examples include water (H₂O), ammonia (NH₃), and ethyl alcohol (C₂H₅OH).
    • Phosphorus exists as a tetratomic molecule (P₄) while sulfur commonly forms an octatomic molecule (S₈).

    The Mole Concept

    • The mole, denoted as "mol", is the unit for measuring the amount of substance containing an equivalent number of entities as in 0.012 kg of carbon-12.
    • Avogadro's number, (6.02 \times 10^{23}), indicates the number of elementary entities in one mole of a substance.
    • The mass of one mole of atoms or molecules is referred to as molar mass.

    Chemical Reactions and Mole Calculations

    • Chemical reactions, such as the combination of hydrogen and oxygen to form water, can be represented by balanced chemical equations.
    • The concept of moles facilitates counting reactants and products in chemical reactions, providing a systematic way to represent and calculate reaction yields.

    Laws of Chemical Composition

    • Law of Constant Proportions states that a compound contains elements in a fixed mass ratio.
    • Law of Multiple Proportions indicates that when elements form more than one compound, the masses of one element that combine with a fixed mass of another are in simple whole number ratios.

    Key Chemical Formula Writing

    • Knowledge of atomic charges and valency is crucial in writing correct chemical formulas for compounds created from various ions.
    • Examples of ion combinations include calcium phosphate (Ca_3(PO_4)_2) and sodium sulfate (Na_2SO_4).

    Fundamental Definitions

    • An atom is the smallest particle retaining element properties, while a molecule is the smallest unit of a substance that can exist independently.
    • Relative atomic masses of elements are compared to that of C-12, which is assigned an atomic mass unit of 12.

    These key points provide a comprehensive overview of atomic structure, isotopes, molecules, the mole concept, laws of composition, and fundamental chemical definitions.

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