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) indicate the number of occupied electron shells in an atom.
Metals are located on the left and center of the table; they typically lose electrons to form positive cations ().
Non-metals are located on the right side; they typically gain electrons to form negative anions ().
Atomic Radius: Generally increases down a group (more shells) and decreases across a period from left to right (greater nuclear charge pulling electrons closer).
Group 1 (Alkali Metals): Reactivity increases down the group because the valence electron is further from the nucleus ().
Group 17 (Halogens): Reactivity decreases down the group as it becomes harder to attract an incoming electron ().
Group 18 (Noble Gases): Possess a full valence shell (e.g., or electrons), making them chemically inert/unreactive.
📐Formulae
💡Examples
Problem 1:
An isotope of Phosphorus has an atomic number and a mass number . Calculate the number of neutrons () and provide the electronic configuration for a neutral Phosphorus atom.
Solution:
; Electronic Configuration: .
Explanation:
The number of neutrons is found using . For a neutral atom, electrons equal protons (). Following the rule, the first shell holds , the second holds , and the remaining go into the third shell.
Problem 2:
Magnesium () is in Group 2. Predict the charge of a Magnesium ion and write its chemical symbol with the charge.
Solution:
Explanation:
Elements in Group 2 have valence electrons. To achieve a stable full outer shell, Magnesium loses these electrons. Since it loses two negative charges, the resulting ion has a charge of .
Problem 3:
Compare the atomic radius of Sodium (, ) and Chlorine (, ), both in Period 3.
Solution:
The atomic radius of is larger than the atomic radius of .
Explanation:
Both elements have electrons in three shells. However, Chlorine has more protons () than Sodium (). This higher nuclear charge exerts a stronger pull on the electrons, drawing them closer to the nucleus and making the atom smaller.