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) indicate the number of valence electrons. Elements in the same group share similar chemical properties (e.g., Group 1 elements have valence electron).
Periods (horizontal rows) indicate the number of occupied electron shells (e.g., Period 3 elements have electrons in shells).
Atomic Radius trend: Decreases across a period from left to right because the increasing nuclear charge () pulls the electron shells closer. It increases down a group as the number of electron shells increases.
Group 1 (Alkali Metals) Reactivity: Increases down the group. As the atomic radius increases, the outer electron is further from the nucleus and more easily lost ().
Group 7 (Halogens) Reactivity: Decreases down the group. Smaller atoms (, ) have a stronger nuclear pull to attract an extra electron into their outer shell compared to larger atoms (, ).
Metallic character: Decreases across a period (moving from metals to non-metals) and increases down a group.
Group 0/8 (Noble Gases): These are monatomic gases with a full outer shell (e.g., has , has ), making them chemically inert/unreactive.
📐Formulae
(Group 1 Reaction with Water)
(Halogen Displacement)
(Effective Nuclear Charge approximation)
(Reduction of a Halogen atom)
💡Examples
Problem 1:
Explain why Potassium () is more reactive than Lithium ().
Solution:
has more electron shells than .
Explanation:
Potassium () is in Period 4, while Lithium () is in Period 2. The single valence electron in is further from the nucleus and experience more 'shielding' from inner shells. This weaker electrostatic attraction makes it easier for to lose its outer electron to form a ion.
Problem 2:
Predict the products and observe if a reaction occurs when Chlorine gas () is bubbled through a solution of Sodium Bromide ().
Solution:
Explanation:
Chlorine () is higher in Group 7 than Bromine (), making it more reactive. A more reactive halogen will displace a less reactive halide from its salt. The solution will turn from colorless to orange/brown due to the formation of aqueous bromine ().
Problem 3:
Describe the trend in atomic radius across Period 3 ( to ).
Solution:
The atomic radius decreases.
Explanation:
As we move from to , the number of protons in the nucleus increases (increasing the nuclear charge). Since the electrons are being added to the same energy level (shell), the increased positive charge pulls the electrons closer to the nucleus, reducing the size of the atom.