1. What is the modern periodic law?
Answer: The modern periodic law states that the properties of elements are a periodic function of their atomic numbers.
2. Describe the present form of the periodic table.
Answer: The present periodic table is arranged in order of increasing atomic number. It consists of 18 vertical columns called groups and 7 horizontal rows called periods.
3. What are s-block elements?
Answer: s-block elements are those in which the last electron enters the s orbital. They include elements in groups 1 and 2, such as alkali metals and alkaline earth metals.
4. What are p-block elements?
Answer: p-block elements are those in which the last electron enters the p orbital. They include elements in groups 13 to 18, including the nonmetals, metalloids, and some metals.
5. What are d-block elements?
Answer: d-block elements, also known as transition metals, are those in which the last electron enters the d orbital. They are found in groups 3 to 12 of the periodic table.
6. What are f-block elements?
Answer: f-block elements, also known as inner transition metals, include the lanthanides and actinides, in which the last electron enters the f orbital.
7. What is atomic radius?
Answer: The atomic radius is the distance from the center of the nucleus to the outermost electron shell of an atom.
8. How does atomic radius change across a period?
Answer: Atomic radius decreases across a period from left to right due to an increase in nuclear charge, which pulls the electron cloud closer to the nucleus.
9. How does atomic radius change down a group?
Answer: Atomic radius increases down a group because each successive element has an additional electron shell, increasing the distance between the nucleus and the outermost electrons.
10. What is ionization enthalpy?
Answer: Ionization enthalpy is the energy required to remove an electron from a gaseous atom or ion.
11. How does ionization enthalpy change across a period?
Answer: Ionization enthalpy generally increases across a period from left to right due to increasing nuclear charge, which makes it harder to remove an electron.
12. How does ionization enthalpy change down a group?
Answer: Ionization enthalpy decreases down a group because the outer electrons are further from the nucleus and experience less electrostatic pull, making them easier to remove.
13. What is electron gain enthalpy?
Answer: Electron gain enthalpy is the energy change that occurs when an electron is added to a neutral atom in the gaseous state to form a negative ion.
14. How does electron gain enthalpy change across a period?
Answer: Electron gain enthalpy generally becomes more negative across a period from left to right, indicating a greater tendency to gain electrons due to increasing nuclear charge.
15. How does electron gain enthalpy change down a group?
Answer: Electron gain enthalpy becomes less negative down a group because the added electron is further from the nucleus and experiences less attraction.
16. What is valence?
Answer: Valence is the combining capacity of an element, typically measured by the number of hydrogen atoms an element can combine with or displace in a compound.
17. How do oxidation states vary across the periodic table?
Answer: Oxidation states generally increase across a period as elements have more valence electrons to lose or share, and they can exhibit multiple oxidation states, especially transition metals.
18. What are the periodic trends in chemical reactivity for metals?
Answer: For metals, chemical reactivity increases down a group as ionization energy decreases, making it easier to lose electrons. It decreases across a period as ionization energy increases.
19. What are the periodic trends in chemical reactivity for nonmetals?
Answer: For nonmetals, chemical reactivity decreases down a group as electron gain enthalpy becomes less negative. It increases across a period as electron gain enthalpy becomes more negative.
20. Why do elements in the same group exhibit similar chemical properties?
Answer: Elements in the same group have the same number of valence electrons, which determines their chemical behavior and reactivity, leading to similar chemical properties.