Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The Periodic Table is arranged by increasing atomic number . Periods are horizontal rows indicating the number of electron shells, while Groups are vertical columns indicating the number of valence electrons.
Across a Period (left to right): Atomic radius decreases due to increased nuclear charge pulling electrons closer; electronegativity and ionization energy generally increase.
Down a Group: Atomic radius increases due to the addition of electron shells; electronegativity and ionization energy decrease as valence electrons are further from the nucleus and more shielded.
Group 1 (Alkali Metals): Reactivity increases down the group. They have 1 valence electron and form ions. For example, .
Group 17 (Halogens): Exist as diatomic molecules (e.g., ). Reactivity decreases down the group. A more reactive halogen will displace a less reactive one from its halide solution: .
Group 0/18 (Noble Gases): Unreactive/inert monoatomic gases with a full outer shell (octet), such as .
Metallic to Non-metallic transition: Elements on the left are metallic (form basic oxides like ), while elements on the right are non-metallic (form acidic oxides like ).
📐Formulae
💡Examples
Problem 1:
Explain the trend in reactivity of Group 1 metals as you go down the group from to .
Solution:
Reactivity increases down Group 1.
Explanation:
Down the group, the number of electron shells increases. The valence electron becomes further from the positive nucleus, and the shielding effect from inner shells increases. Consequently, the electrostatic attraction between the nucleus and the valence electron weakens, making it easier for the atom to lose its outer electron to form a cation (e.g., ).
Problem 2:
Predict the physical state and color of Astatine () at room temperature based on the trends in Group 17.
Solution:
Astatine is a dark-colored (black) solid.
Explanation:
In Group 17, melting and boiling points increase down the group as the molecules get larger, leading to stronger intermolecular forces (London dispersion forces). and are gases, is a liquid, and is a solid. Following this trend, must be a solid. The colors also darken down the group ( is pale green, is grey/purple).
Problem 3:
Why does the atomic radius decrease from to across Period 3?
Solution:
Increased nuclear charge with constant shielding.
Explanation:
Moving from to , the atomic number increases, meaning there are more protons in the nucleus. However, the number of occupied electron shells remains the same (constant shielding). The stronger positive charge of the nucleus exerts a greater pull on the electrons, drawing them closer and resulting in a smaller atomic radius.