What is the periodic table?

The periodic table arranges elements in order of increasing atomic number, grouping elements with similar properties together.

What are groups and periods?

Groups are vertical columns of elements with similar properties; periods are horizontal rows showing trends in properties.

Are these notes useful for competitive exams?

Yes, these notes help students prepare for NEET, SSC, Railway, Police Bharti exams as well as Class 10 board exams.

1. What is periodic classification of elements?

Periodic classification arranges elements in a table so that elements with similar properties recur periodically when ordered by increasing atomic number.

2. What were the main features of Mendeleev's periodic table?

Modern periodic law: properties of elements are periodic functions of their atomic numbers (Z). This resolves anomalies caused by isotopes and places elements correctly by Z, not atomic weight.

4. What is a period and what is a group in the periodic table?

Aperiodis a horizontal row; elements in a period have the same number of electron shells. Agroupis a vertical column; elements in a group have similar valence electron configurations and chemical properties.

5. How many groups and periods are there in the modern periodic table?

The modern periodic table has18 groupsand7 periods(excluding the lanthanoids and actinoids which are placed separately as f-block).

6. How does electronic configuration determine element position in the periodic table?

Elements are placed into blocks (s, p, d, f) and groups according to their valence electron configuration. The valence electrons largely determine chemical reactivity and group properties.

8. What is valency and how is it determined from electronic configuration?

Valency is the combining capacity of an element, generally equal to the number of electrons lost, gained or shared to achieve a noble gas configuration. From electronic configuration, valency is determined by the number of valence electrons (or 8 − valence electrons for main-group elements).

11. What is ionization energy and what are its trends?

Ionization energy is the energy required to remove an electron from a gaseous atom.Across a period:increases (atoms hold electrons tightly).Down a group:decreases (outer electrons are farther and shielded).

12. Define electron affinity and electronegativity. How are they different?

Electron affinity is the energy change when an atom gains an electron (in gas phase). Electronegativity is a relative measure of an atom's ability to attract bonding electrons. Electronegativity is a periodic property used in bonds; electron affinity is a measurable energy change.

13. What is the trend of electronegativity across a period and down a group?

Electronegativity generallyincreases across a period(stronger nuclear attraction) anddecreases down a group(increased distance and shielding).

14. How does metallic vs non-metallic character change across a period and down a group?

Across a period:metallic character decreases, non-metallic increases.Down a group:metallic character increases (atoms more willing to lose electrons).

15. Where is hydrogen placed and why is its position considered special?

Hydrogen is placed in group 1 by many tables due to its 1s¹ configuration, but it shares properties with group 1 (forms H⁺) and group 17 (forms H⁻ in hydrides). Its behavior is unique, so its placement is often shown separately.

19. What are transition elements and name some characteristic properties?

Transition elements are d-block elements showing variable oxidation states, form coloured compounds, and often act as catalysts (e.g., Fe, Cu, V, Mn).

20. How does metallic reactivity change across a period and down a group?

Across a period, metallic reactivity decreases (atoms less willing to lose electrons). Down a group, metallic reactivity increases (outer electrons are easier to lose).

21. What is ionic radius? How does ionic radius change for cations and anions across a period?

Cations (positive) are smaller than parent atoms; anions (negative) are larger. Across a period ionic radii vary with charge and type; general trend: cations decrease size across period; anions also show size changes but depend on exact element.

23. Why are noble gases chemically inert?

They have complete valence shells (stable electronic configuration), so they have little tendency to gain, lose or share electrons, making them largely unreactive.

24. Given electronic configuration 2,8,6 which group does the element belong to?

Valence electrons = 6 → group 16 (oxygen family). The element is oxygen (atomic number 8).

27. What is periodicity and why is it important?

Periodicity is the recurring variation of properties of elements when arranged by atomic number. It is important because it helps predict behaviour and chemical properties of elements.

28. Why do elements of the same group show similar chemical properties?

Because they have the same number of valence electrons and similar valence shell configurations, leading to similar chemical behavior (e.g., group 1 elements all form +1 ions).

31. What anomalies did Mendeleev face when arranging by atomic weight?

Some elements did not fit when ordered strictly by atomic weight (e.g., iodine and tellurium) — ordering by atomic number resolved these anomalies.

32. Where are lanthanoids and actinoids placed and why are they shown below the main table?

They belong to the f-block and are placed separately to keep the table compact. Lanthanoids (4f) and actinoids (5f) have filling f-orbitals and similar properties within series.

Class 10 Science — Chapter 5: Periodic Classification of Elements

By RAAM SETU | NEET, SSC, Railway & Police Bharti Focused Notes 📘

📘 Introduction

This chapter explains the Periodic Classification of Elements, covering the periodic table, groups, periods, trends in reactivity, and properties of metals & non-metals. Essential for NEET, SSC, Railway, Police Bharti exams and Class 10 board exams.

🔹 Key Concepts

Periodic Table: Arrangement of elements by atomic number
Groups: Vertical columns showing similar properties
Periods: Horizontal rows showing trends in properties
Reactivity Trends: Metals: increases down groups; Non-metals: decreases down groups
Valency: Determines chemical bonding

📊 Chapter Summary Table

Concept	Example / Trend	Use
Group 1 Elements	Li, Na, K	Highly reactive metals, form salts
Group 17 Elements	F, Cl, Br	Highly reactive non-metals, form halides
Period Trends	Atomic size decreases across period	Predicts chemical behavior

🧮 Practice Questions

What is the periodic table? ➡ Show Answer
The periodic table arranges elements in order of increasing atomic number, grouping elements with similar properties together.
Define groups and periods. ➡ Show Answer
Groups are vertical columns with similar properties; periods are horizontal rows showing trends across elements.
Mention one trend of reactivity in metals and non-metals. ➡ Show Answer
Metal reactivity increases down a group; non-metal reactivity decreases down a group.

Periodic Classification of Elements — 50 Q&A

NCERT Class 10. Mobile-friendly notes — tap to expand answers.

Light / Dark

Groups & Periods Periodic Trends Electronic Config Mendeleev vs Modern

NCERT Class 10 — Periodic Classification

📘 Introduction

🔹 Key Concepts

📊 Chapter Summary Table

🧮 Practice Questions

1. What is periodic classification of elements?

2. What were the main features of Mendeleev's periodic table?

3. State the modern periodic law and why it improved Mendeleev's table.

4. What is a period and what is a group in the periodic table?

5. How many groups and periods are there in the modern periodic table?

6. How does electronic configuration determine element position in the periodic table?

7. What are s-, p-, d-, and f-blocks? Give examples.

8. What is valency and how is it determined from electronic configuration?

9. Write the electronic configuration of sodium (Z = 11).

10. Define atomic radius. Describe its trend across a period and down a group.

11. What is ionization energy and what are its trends?

12. Define electron affinity and electronegativity. How are they different?

13. What is the trend of electronegativity across a period and down a group?

14. How does metallic vs non-metallic character change across a period and down a group?

15. Where is hydrogen placed and why is its position considered special?

16. What are inert (noble) gases? List some properties and uses.

17. Describe properties and uses of alkali metals (group 1).

18. Describe properties and uses of halogens (group 17).

19. What are transition elements and name some characteristic properties?

20. How does metallic reactivity change across a period and down a group?

21. What is ionic radius? How does ionic radius change for cations and anions across a period?

22. What is the diagonal relationship in the periodic table? Give an example.

23. Why are noble gases chemically inert?

24. Given electronic configuration 2,8,6 which group does the element belong to?

25. How many valence electrons do group 2 elements have? Give examples.

26. How to determine the period of an element from electronic configuration? (Example: 2,8,1)

27. What is periodicity and why is it important?

28. Why do elements of the same group show similar chemical properties?

29. Give an example showing how metallic character changes down a group.

30. Quick visual: Trend of atomic radius across a period and down a group.

31. What anomalies did Mendeleev face when arranging by atomic weight?

32. Where are lanthanoids and actinoids placed and why are they shown below the main table?

33. Which element has the highest electronegativity and why?

34. Which atom is larger: Na or K? Why?

35. Which has higher ionization energy: Na or Mg? Explain.

36. Why is chlorine more reactive than bromine among halogens?

37. How does boiling point generally change across a period and down a group?

38. How can you identify metals, non-metals and metalloids from the periodic table?

39. Why do elements in the same period show different properties? Give an example.

40. How is the periodic table useful in predicting element properties?

41. Electronic configuration of chlorine (Z = 17). Which group and period does it belong to?

42. How did Moseley contribute to the periodic table?

43. Predict properties of an element in period 3, group 16.

44. What is atomic number (Z)?

45. What are isotopes and do they affect periodic classification?

46. Use the periodic table to predict oxide formula for an element with valence 2.

47. What is electropositivity and which common element is most electropositive?

48. Identify the element with electronic configuration 2,8,3 and state group and valency.

49. Why is arranging elements by atomic number useful for predicting reactivity?

50. Quick revision: High-yield points for Periodic Classification.