Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Elements are arranged in the Periodic Table in order of increasing atomic (proton) number .
Groups (vertical columns) contain elements with the same number of outer-shell (valency) electrons, determining their chemical properties.
Periods (horizontal rows) indicate the number of occupied electron shells in an atom.
Group 1 (Alkali Metals) are soft metals that react with water to form alkaline solutions. Reactivity increases down the group as the distance between the nucleus and the outer electron increases, making the electron easier to lose: .
Group 7 (Halogens) are diatomic non-metals (). Reactivity decreases down the group because increased shielding makes it harder to attract an incoming electron to form a ion.
Group 0 (Noble Gases) are monatomic and chemically inert due to having a stable, full outer shell of electrons (a 'stable octet', except for which has 2).
Transition Elements are found in the center of the table; they have high densities, high melting points, form colored compounds, and exhibit variable oxidation states such as and .
Across a period from left to right, elements change from metallic to non-metallic character.
📐Formulae
(Group 1 reaction with water)
(Halogen displacement where is more reactive than )
(Calculating moles for stoichiometric reactions in the Periodic Table)
(Atomic number equals number of protons)
💡Examples
Problem 1:
Write the balanced chemical equation for the reaction between Sodium () and Water (), and state the observations.
Solution:
Explanation:
Sodium floats, fizzes (due to gas), and eventually disappears to form a colorless solution of sodium hydroxide (), which is alkaline. The atom loses one electron to become a ion.
Problem 2:
Predict and explain the reaction when Chlorine gas () is bubbled through a solution of Potassium Iodide ().
Solution:
(The solution turns brown/dark orange).
Explanation:
This is a displacement reaction. Chlorine is higher in Group 7 than Iodine, making it more reactive (a stronger oxidizing agent). Therefore, displaces ions from the solution, forming (iodine).
Problem 3:
An element has the electronic configuration . Identify its Group and Period.
Solution:
Group 7, Period 3.
Explanation:
The number of valency electrons (7) determines the Group. The number of occupied shells (3) determines the Period. This element is Chlorine ().