Early Theories of Matter
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Questions and Answers

What happens to electron affinity as electrons are placed in higher energy levels farther from the nucleus?

  • It remains unchanged.
  • It decreases and becomes more negative. (correct)
  • It increases and becomes more positive.
  • It decreases and becomes less negative.

    • What defines electronegativity?

  • The attraction an atom has for electrons. (correct)
  • The repulsion between electrons.
  • The number of protons in an atom.
  • The determinant of atomic mass.

    • What is the trend for electronegativity as you move down a group in the periodic table?

  • It increases due to larger atomic radius.
  • It increases due to stronger nuclear pull.
  • It decreases due to increasing atomic number. (correct)
  • It remains constant across a group.

    • Which type of compound consists of non-metal and non-metal elements?

    <p>Molecular compounds.</p> Signup and view all the answers

    What property is typically associated with ionic compounds?

    <p>Rigid and brittle structure.</p> Signup and view all the answers

    Which statement accurately describes intramolecular forces?

    <p>They bind atoms and ions together within a compound.</p> Signup and view all the answers

    What is a common characteristic of electrolytes in the body?

    <p>They are minerals that conduct electricity.</p> Signup and view all the answers

    What happens to the solubility in water of ionic compounds compared to molecular compounds?

    <p>Ionic compounds tend to have higher solubility.</p> Signup and view all the answers

    What did Democritus believe about atoms?

    <p>Atoms were uniform, solid, and indestructible.</p> Signup and view all the answers

    Which statement accurately reflects Dalton's Atomic Theory?

    <p>All atoms are identical in size and mass.</p> Signup and view all the answers

    What did Rutherford's research indicate about the structure of an atom?

    <p>The positive charge is found in a small concentrated volume.</p> Signup and view all the answers

    What is the correct definition of an isotope?

    <p>Atoms with the same number of protons but different neutrons.</p> Signup and view all the answers

    Which particle has the largest relative mass?

    <p>Both proton and neutron</p> Signup and view all the answers

    What happens to atomic radius as you move from left to right across a period?

    <p>It decreases due to increased nuclear charge.</p> Signup and view all the answers

    What is the formula to calculate the number of neutrons in an atom?

    <p>Atomic Mass - Atomic Number</p> Signup and view all the answers

    Why does the atomic radius increase down a group on the periodic table?

    <p>Increased distance between the nucleus and the outermost orbitals.</p> Signup and view all the answers

    Which ion has a +2 charge?

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

    What type of bond is indicated by a ΔEN greater than 1.7?

    <p>Ionic bond</p> Signup and view all the answers

    What defines a diatomic molecule?

    <p>Two atoms of the same or different elements chemically bonded</p> Signup and view all the answers

    Which intermolecular force is considered the weakest?

    <p>London dispersion force</p> Signup and view all the answers

    What is the bonding capacity of an atom?

    <p>The number of covalent bonds it can form</p> Signup and view all the answers

    Which of the following describes the octet rule?

    <p>Atoms want to have eight valence electrons in their outer shell</p> Signup and view all the answers

    What principle describes the relationship between intermolecular forces and boiling/melting points?

    <p>Stronger intermolecular forces result in higher melting and boiling points</p> Signup and view all the answers

    Which molecular interaction involves a hydrogen atom attached to a highly electronegative atom?

    <p>Hydrogen bonding</p> Signup and view all the answers

    What two particles are primarily responsible for the mass of an atom?

    <p>Neutrons and protons</p> Signup and view all the answers

    What is the shielding effect in atomic structure?

    <p>The decrease in the nucleus's attraction on valence electrons due to inner shell electrons</p> Signup and view all the answers

    Why is the ionic radius of an anion larger than that of its neutral atom?

    <p>Adding electrons increases electron-electron repulsion in the ion</p> Signup and view all the answers

    What trend does ionization energy follow as you move down a group in the periodic table?

    <p>Ionization energy decreases due to increased distance from the nucleus</p> Signup and view all the answers

    What defines first ionization energy?

    <p>The energy required to remove the outermost electron from a neutral atom</p> Signup and view all the answers

    Which of the following statements is true about electron affinity?

    <p>Both B and C are correct</p> Signup and view all the answers

    What happens to electron affinity values as you move across a period in the periodic table?

    <p>They become more negative due to increasing nuclear attraction</p> Signup and view all the answers

    What causes Al3+ ions to be smaller than Na+ ions?

    <p>Al3+ has more protons attracting the remaining electrons</p> Signup and view all the answers

    Study Notes

    Early Theories of Matter

    • Democritus believed matter was composed of indivisible particles called atoms, which were uniform, solid, hard, incompressible, and indestructible. Atoms moved in infinite numbers through empty space until stopped.
    • Aristotle proposed that all materials on Earth were made of four elements: Earth, Fire, Water, and Air. He believed all substances were made of small amounts of these four elements.
    • Dalton's Atomic Theory proposed that:
      • All matter is composed of extremely small particles called atoms.
      • Atoms of a given element are identical in size, mass, and other properties.
      • Atoms of different elements differ in size, mass, and other properties.
      • Atoms cannot be subdivided, created, or destroyed.
    • Thomson discovered electrons, which were negatively charged subatomic particles found within all atoms.
    • Nagaoka proposed an atomic model with a small nucleus surrounded by a ring of electrons.
    • Rutherford discovered that the positive charge and most of the mass of an atom are concentrated in an extremely small volume called the nucleus.
    • Chadwick discovered neutrons, which are neutral subatomic particles found in the nucleus. He shot particles through gold to make this discovery

    Subatomic Particles

    • Proton: Located in the nucleus, with a relative mass of 1 and a charge of 1+.
    • Neutron: Located in the nucleus, with a relative mass of 1 and a charge of 0.
    • Electron: Located in orbitals around the nucleus, with a relative mass of 1/1838.65 and a charge of 1-.

    Atomic Structure and Terminology

    • Atomic Number (Z): The number of protons in an atom's nucleus.
    • Mass Number (A): The sum of protons and neutrons in an atom's nucleus.
    • Isotopes: Atoms of the same element that have the same number of protons but different numbers of neutrons.
    • Relative Atomic Mass (Aᵣ): The weighted average of the masses of all naturally occurring isotopes of an element.
    • Unified Atomic Mass Unit (u): A unit of mass used to express atomic masses, defined as 1/12 the mass of a carbon-12 atom.
    • Atomic radius: The distance from an atom's nucleus to the furthest orbital of electrons.
    • Shielding effect: The decrease in the nucleus's force of attraction on valence electrons due to the existence of electrons in the inner shells.
    • Ionic radius: The distance from the nucleus of an ion up to which it has an influence on its electron cloud.

    Properties of Ionic and Covalent Compounds

    Property Ionic Molecular
    Type of Elements Present Metal + non-metal Non-metal + non-metal
    Type of Bonding Ionic/Covalent Ionic/Covalent
    Electron Behaviour Transferred/Shared Transferred/Shared
    Smallest Unit Formula unit/Molecule Formula unit/Molecule
    State at Room Temp Solid/Liquid/Gas Solid/Liquid/Gas
    Melting Point Relatively high/Low Relatively high/Low
    Electrical Conductivity Yes/No Yes/No
    Solubility in Water Relatively high/Low Relatively high/Low

    Intermolecular forces

    • London dispersion force: Weakest intermolecular force, occurs between all molecules, involves temporary dipoles.
    • Dipole-dipole force: Occurs between polar molecules due to permanent dipoles.
    • Hydrogen bonding: Strongest intermolecular force, occurs between molecules containing a hydrogen atom bonded to a highly electronegative atom (like oxygen, nitrogen, or fluorine).

    Ionization Energy

    • Ionization Energy: The amount of energy required to remove an electron from an isolated atom or molecule.
    • First ionization energy: The energy needed to remove the outermost, or highest energy, electron from a neutral atom in the gas phase.
    • Second ionization energy: The energy required to remove the outermost, or least bound, electron from a 1+ ion of the element.

    Electron Affinity

    • Electron affinity: The change in energy (in kJ/mol) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion.

    Electronegativity

    • Electronegativity: A chemical property that describes the tendency of an atom or a functional group to attract electrons toward itself.
    • Trends in electronegativity:
      • Increases across a period due to increasing nuclear charge.
      • Decreases down a group due to increasing atomic radius.

    Other Important Concepts

    • Delta EN: The difference in electronegativity between two atoms in a bond.
      • ΔEN = 0 (non-polar covalent bond)
      • ΔEN < 1.7 (polar covalent bond)
      • ΔEN > 1.7 (ionic bond)
    • Diatomic molecule: A molecule composed of two atoms.
    • Polyatomic molecule: A molecule composed of three or more atoms.
    • Lone pair: A pair of valence electrons that are not involved in bonding.
    • Octet rule: The tendency of atoms to gain, lose, or share electrons to achieve a stable configuration with eight valence electrons.
    • Structural formula: A diagram showing the arrangement of atoms and bonds within a molecule.
    • Bonding capacity: The number of chemical bonds an atom can form.

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    SCH3U1 Unit 1 Study Notes PDF

    Description

    Explore the foundational theories of matter through the insights of key philosophers and scientists. From Democritus's indivisible atoms to Dalton's atomic theory and the discoveries by Thomson and Rutherford, this quiz covers the evolution of our understanding of matter. Test your knowledge on these historical concepts and their significance in science.

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