Trends in Elemental Properties and Atomic Structure

Trends in the Properties of Elements

• Elements in the periodic table exhibit trends or regular changes in their properties.
• These trends are influenced by the arrangement of electrons in the atoms.

Valence Electrons

• The outermost electrons in an atom, called valence electrons, play a significant role in determining an element's properties.
• Key Points:
  • The number of valence electrons is constant for elements within the same group.
  • The number of valence electrons increases as you move across a period (from left to right).

Non-Reactivity of Noble Gases

• Noble gases are chemically inert due to having a complete set of valence electrons (8 electrons in their outer shell).
• Reactivity of other elements depends on their ability to gain, lose, or share electrons to reach a full outer shell.

Atomic Size Trends

• Atomic size increases:
  • Down a group (top to bottom): As additional energy levels (shells) of electrons are added, the atom's size increases.
  • Across a period (left to right): Atomic size decreases as the positive charge in the nucleus increases, pulling the electron cloud closer to the nucleus.

Review Questions

1. Draw a Bohr-Rutherford model of an atom with one valence electron.
2. Examine the diagram: How many valence electrons does the element one position to the right on the periodic table have?
3. Which has more valence electrons: Aluminum or phosphorus?
4. Carbon's Valence Electrons: Explain how the four valence electrons allow carbon to bond with other elements. Name another element that shares this property.
5. Reactivity Comparison: Explain why halogens are more reactive than noble gases.
6. Atomic Size Trends: What happens to atom sizes as you move across a period? And down a group?
7. Size Comparison: Based on Figure 5.25, which atom is larger: oxygen or sulfur?
8. Reactivity Comparison: Between magnesium and calcium, which is more reactive? Provide reasoning.
9. Model for Trends: Describe a model that illustrates the trends in atomic sizes.
10. Reactivity of Potassium vs. Sodium: Why is potassium, the larger atom, more reactive? Explain.

Summary of Section 5.4

• The number of valence electrons indicates the position of an element in the periodic table.
• Understanding these trends is crucial for predicting behavior and reactions of elements.