Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The Periodic Table is arranged by increasing atomic number (), which represents the number of protons in the nucleus.
Groups (vertical columns) contain elements with the same number of valence electrons, resulting in similar chemical properties.
Periods (horizontal rows) represent the number of occupied electron shells. For example, elements in Period 3 have electrons in 3 energy levels.
Atomic Radius: Decreases across a period due to increasing nuclear charge () pulling electrons closer, and increases down a group as additional electron shells are added.
First Ionization Energy: The energy required to remove one mole of electrons from one mole of gaseous atoms. It increases across a period and decreases down a group.
Electronegativity: A measure of an atom's ability to attract a shared pair of electrons in a chemical bond. Trends follow the same pattern as Ionization Energy (increases across, decreases down).
Metallic Character: Refers to the level of reactivity of a metal. It decreases across a period and increases down a group.
Valence Electrons: The electrons in the outermost shell that determine bonding behavior. Group 1 elements have valence electron, while Group 17 elements have .
📐Formulae
💡Examples
Problem 1:
Explain why the atomic radius of Fluorine () is smaller than the atomic radius of Lithium (), even though Fluorine has more electrons.
Solution:
has a higher nuclear charge () than ().
Explanation:
Both elements are in Period 2, meaning they have the same number of electron shells. However, Fluorine has more protons in its nucleus, creating a stronger positive pull on the same number of shells, which draws the electrons inward and reduces the radius.
Problem 2:
Which element has a higher first ionization energy: Potassium () or Sodium ()?
Solution:
Sodium () has a higher first ionization energy.
Explanation:
Sodium is above Potassium in Group 1. has fewer electron shells (3) than (4). In , the valence electron is closer to the nucleus and experiences less 'shielding' from inner electrons, meaning the electrostatic attraction is stronger and more energy is required to remove the electron.
Problem 3:
Identify the element with the electron configuration and predict its group and period.
Solution:
The element is Chlorine (). It is in Group 17 and Period 3.
Explanation:
The number of shells (3) indicates Period 3. The number of valence electrons (7) indicates Group 17 (Halogens). The total number of electrons is , which corresponds to the atomic number of Chlorine ().