Chemistry Lesson 3: Periodic Trends

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Questions and Answers

Explain why the atomic radius of atoms generally decreases as you move from left to right across a period on the periodic table.

As you move across a period, the number of protons in the nucleus increases, leading to a stronger attraction between the nucleus and the electrons. This stronger attraction pulls the electrons closer to the nucleus, resulting in a smaller atomic radius.

Explain why the atomic radius of atoms generally increases as you move down a group on the periodic table.

As you move down a group, the number of electron shells increases. The outermost electrons are located farther from the nucleus, leading to a larger atomic radius.

Explain the difference between atomic radius and ionic radius.

Atomic radius refers to the size of a neutral atom, while ionic radius refers to the size of an ion, an atom that has gained or lost electrons.

Why do positively charged ions (cations) typically have a smaller ionic radius compared to their neutral atom counterparts?

<p>Positively charged ions have lost electrons, resulting in a reduced electron-electron repulsion. This allows the remaining electrons to be pulled closer to the nucleus, resulting in a smaller ionic radius.</p> Signup and view all the answers

Explain why negatively charged ions (anions) typically have a larger ionic radius compared to their neutral atom counterparts.

<p>Negatively charged ions have gained electrons. The increased electron-electron repulsion pushes the electrons further away from the nucleus, leading to a larger ionic radius.</p> Signup and view all the answers

Explain why the first ionization energy generally increases from left to right across a period in the periodic table.

<p>First ionization energy increases from left to right across a period because the effective nuclear charge increases. As the number of protons in the nucleus increases, the attraction between the nucleus and the valence electrons becomes stronger, making it more difficult to remove an electron.</p> Signup and view all the answers

Describe the general trend for electronegativity down a group and across a period in the periodic table and provide a reason for this trend.

<p>Electronegativity decreases down a group and increases across a period. Electronegativity decreases down a group because the atomic radius increases, leading to weaker attraction between the nucleus and valence electrons. Across a period, electronegativity increases because the effective nuclear charge increases, strengthening the attraction between the nucleus and valence electrons.</p> Signup and view all the answers

Explain how the octet rule relates to the tendency of atoms to gain, lose, or share electrons.

<p>The octet rule states that atoms tend to gain, lose, or share electrons in order to achieve a full set of eight valence electrons. This stable configuration resembles the electron configuration of noble gases, which are unreactive due to their filled outer shells.</p> Signup and view all the answers

Describe how the ionic radii of negative ions generally change as you move from left to right across a period, beginning with group 15 or 16. Explain why.

<p>The ionic radii of negative ions generally decrease from left to right across a period, starting at group 15 or 16. This is because the effective nuclear charge increases as you move across the period. Even though the number of electron shells remains the same, the increasing number of protons in the nucleus attracts the electrons more strongly, causing the ionic radius to shrink.</p> Signup and view all the answers

Explain why the first ionization energy generally decreases down a group in the periodic table.

<p>First ionization energy decreases down a group because the atomic size increases. As the number of electron shells increases, the valence electrons are further away from the nucleus. This leads to weaker attraction between the nucleus and the valence electrons, making it easier to remove an electron.</p> Signup and view all the answers

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Flashcards

Atomic Radius

The distance from the nucleus to the outermost shell of electrons.

Periodic Trend

A predictable pattern of properties observed in elements across periods or groups in the periodic table.

Ionic Radius

The radius of an atom's ion, which changes upon gaining or losing electrons.

Ionization Energy

The energy required to remove an electron from an atom.

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Electronegativity

A measure of an atom's ability to attract and hold onto electrons in a bond.

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First Ionization Energy

Energy required to remove the first electron from an atom.

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Octet Rule

Atoms gain, lose, or share electrons to achieve eight valence electrons.

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Atomic Radius Trend

Atomic radius decreases left to right and increases down a group.

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Study Notes

  • Periodic trends are patterns of properties that repeat across the periodic table
  • Understanding these trends helps predict element properties

Focus Questions

  • How can the periodic table be used to predict an element's properties?

New Vocabulary

  • Ion: An atom or group of atoms with a positive or negative charge
  • Ionization energy: The energy needed to remove an electron from a gaseous atom
  • Octet rule: Atoms tend to gain, lose, or share electrons to achieve a full set of eight valence electrons
  • Electronegativity: Relative ability of an atom to attract electrons within a chemical bond

Review Vocabulary

  • Principal energy level: The major energy level of an atom

Atomic Radius

  • Atomic size is a periodic trend influenced by electron configuration
  • The radius of a metal atom is half the distance between two adjacent atoms in a crystal lattice
  • Nonmetal atomic radii are often measured in molecules of two identical atoms
  • Atomic radius generally decreases from left to right within a period due to increasing nuclear charge
  • Atomic radius generally increases as you move down a group due to increasing principal energy levels causing larger electron clouds

Ionic Radius

  • An ion is an atom or group of atoms with a positive or negative charge
  • When atoms form positive ions, they lose electrons becoming smaller; electrostatic repulsion decreases, and electrons are pulled closer
  • When atoms form negative ions, they gain electrons becoming larger; electrostatic repulsion increases pushing the electrons further apart
  • Positive ions generally decrease from left to right; negative ions generally decrease from left to right starting with period 15 or 16

Ionization Energy

  • Ionization energy is the energy required to remove an electron from a gaseous atom
  • First ionization energy: energy to remove the first electron
  • Second ionization energy: energy to remove the second electron
  • Subsequent ionization energy each requires more energy, but not in a perfectly linear pattern
  • First ionization energy generally increases from left to right within a period; decreases as you move down a group
  • The octet rule explains atoms tendency to gain, lose, or share electrons to achieve 8 valence electrons; an exception is the first and second-period metals, they are stable with 2 electrons in the 1s orbital

Electronegativity

  • Electronegativity indicates an element's relative ability to attract electrons within a chemical bond
  • Electronegativity generally decreases as you move down a group and increases as you move left to right across a period

Quiz Questions and Answers

  • Question 1: How is the radius of a metal atom measured?

    • Answer: One-half the distance between two adjacent atoms in a crystal lattice

  • Question 2: Moving left to right within a period, atomic radius generally...

    • Answer: Decreases

  • Question 3: Moving down within a group, atomic radius generally...

    • Answer: Increases

  • Question 4: Moving left to right within a period, first ionization energy...

    • Answer: Increases

  • Question 5: Atoms tend to gain, lose, or share electrons to acquire how many valence electrons?

    • Answer: Eight

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