Kit Library / Science / Chemistry
⚡ Topic Learning KitShared by a Veda learner · Generated with Veda AI
Veda Bites are swipeable micro-lessons — each one teaches exactly one idea. The bites below come from this kit — swipe through them in the app.
💡 Key Idea
Properties repeat with atomic number.
The Modern Periodic Law states that the properties of elements are a periodic function of their atomic number (not atomic mass). This is the foundation of the periodic table.
↳ Atomic number, not mass, governs periodicity.
📖 Definition
Rows and columns organize elements.
A period is a horizontal row (7 periods). A group is a vertical column (18 groups). Elements in the same group have the same valence electron configuration.
↳ Groups share chemical behavior due to valence electrons.
💡 Key Idea
More protons, same shell, smaller radius.
Across a period, effective nuclear charge increases because protons increase while shielding by inner electrons stays constant. This pulls valence electrons closer, decreasing atomic radius.
↳ Increased nuclear charge shrinks atomic size across a period.
💡 Key Idea
New shells add size.
Down a group, new energy shells are added, increasing the principal quantum number. The outermost electrons are farther from the nucleus, so atomic radius increases.
↳ Adding shells down a group enlarges atomic radius.
⭐ Important Fact
Energy to remove an electron.
Ionization enthalpy is the energy required to remove the most loosely bound electron from a gaseous atom. It increases across a period (due to higher nuclear charge) and decreases down a group (due to larger size and shielding).
↳ IE increases across, decreases down.
⭐ Important Fact
Energy change when adding an electron.
Electron gain enthalpy is the energy released when an electron is added to a gaseous atom. Generally, it becomes more negative across a period (easier to add electron) and less negative down a group (due to larger size).
↳ Halogens love electrons; noble gases don't.
💡 Key Idea
How strongly an atom attracts shared electrons.
Electronegativity is the tendency of an atom to attract a shared pair of electrons in a chemical bond. It increases across a period and decreases down a group.
↳ Electronegativity follows the same trend as ionization enthalpy.
⚖️ Comparison
Metals lose, non-metals gain.
Metals tend to lose electrons (low ionization enthalpy), while non-metals gain electrons (high electron gain enthalpy).
↳ Metallic character is opposite to non-metallic character.
⭐ Important Fact
Outer electrons decide group.
For main-group elements, the group number equals the number of valence electrons (for groups 1-2 and 13-18). For example, group 17 elements (halogens) have 7 valence electrons.
↳ Group number = valence electrons for main groups.
⚠️ Common Mistake
Cations shrink, anions swell.
A cation (positive ion) is smaller than its parent atom because it loses an electron shell. An anion (negative ion) is larger because added electrons increase electron-electron repulsion.
↳ Cations are smaller, anions are larger than their atoms.
🎯 Exam Tip
Memorize the periodic trends.
↳ Use the periodic table to predict trends quickly.
🧠 Memory Trick
A simple mnemonic.
For properties that increase across a period (like ionization enthalpy and electronegativity), think 'Right is Tight' – atoms hold electrons more tightly. For down a group, 'Down is Loose' – electrons are less tightly held.
↳ Right is tight, down is loose.
❓ Did You Know
Before atomic numbers.
Dmitri Mendeleev arranged elements by atomic mass and left gaps for undiscovered elements. Later, Henry Moseley showed that atomic number is the fundamental property, leading to the modern periodic law.
↳ Moseley corrected Mendeleev's order.
🛠️ Application
Periodic table as a predictor.
Knowing an element's position lets you predict its reactivity, bonding type, and oxidation states. For example, alkali metals (group 1) are highly reactive and form +1 ions, while halogens (group 17) form -1 ions.
↳ Position in the table dictates chemical personality.
🚫 Warning
Not all trends are perfect.
Some irregularities occur due to half-filled and fully-filled orbitals. For example, ionization enthalpy of nitrogen is higher than oxygen because nitrogen has a stable half-filled p-subshell.
↳ Stability of half-filled orbitals can break trends.
This chapter explains how elements are classified in the periodic table based on atomic number, and how various properties like atomic radius, ionization enthalpy, electron gain enthalpy, and electronegativity show perio…
Full explanation, worked examples & memory tricks in the app
All 17 questions, laddered from warm-up to topper-level, each with its answer and the reasoning behind it.
Q1. Which of the following is the correct order of increasing atomic radii for the elements Li, Be, B, C, N, O, F?
BeginnerC · F < O < N < C < B < Be < Li
Across a period, atomic radius decreases due to increasing effective nuclear charge, so F has the smallest radius and Li the largest.
Q2. Which of the following elements has the highest electronegativity according to Pauling scale?
BeginnerC · F
Fluorine is the most electronegative element on the Pauling scale (3.98).
Q3. Which of the following elements is an alkali metal?
BeginnerD · Na
Sodium (Na) is in Group 1, making it an alkali metal. K is also an alkali metal, but since only one answer is correct, Na is the correct choice.
Q4. Which of the following has the largest atomic radius?
BeginnerA · Te
Atomic radius increases down a group. Among O, S, Se, Te, Te is the lowest in the group and thus has the largest atomic radius.
Q5. Which of the following is the correct order of increasing non-metallic character?
BeginnerD · P < S < Cl
Non-metallic character increases across a period, so P (Group 15) is least non-metallic, followed by S, then Cl.
Q6. Which of the following is the correct order of increasing electronegativity for the elements?
BeginnerB · K < Na < Li
Electronegativity decreases down a group, so K has the lowest electronegativity, followed by Na, then Li.
Q7. The element with the highest electronegativity in the periodic table is chlorine.
BeginnerB · False
Fluorine has the highest electronegativity (3.98), not chlorine.
Q8. Atomic radius generally increases down a group.
BeginnerA · True
Down a group, the number of shells increases, so the atomic radius increases.
Q9. Which element has the highest first ionization enthalpy in the second period?
IntermediateC · Ne
Ionization enthalpy generally increases across a period. Ne, being a noble gas with a stable octet, has the highest first ionization enthalpy in the second period.
Q10. The correct order of electron gain enthalpy (more negative to less negative) for the halogens is:
IntermediateA · Cl > F > Br > I
Chlorine has the most negative electron gain enthalpy among halogens because of its smaller size and effective nuclear charge; fluorine's small size causes electron-electron repulsion, making its electron gain enthalpy less negative than chlorine.
Q11. Which of the following is the correct order of increasing metallic character?
IntermediateC · Al < Mg < Na
Metallic character decreases across a period, so Na (Group 1) is most metallic, followed by Mg, then Al.
Q12. Which of the following is the correct order of electron gain enthalpy (more negative to less negative) for the elements O, S, Se, and Te?
IntermediateA · S > O > Se > Te
Electron gain enthalpy becomes more negative down a group, but oxygen is an exception due to its small size and electron-electron repulsion. Thus, S has the most negative electron gain enthalpy among these.
Q13. Which of the following is the correct order of increasing valence?
IntermediateC · F < O < N
Valence generally increases up to group 15 and then decreases. For N (group 15) valence is 3, O (group 16) valence is 2, F (group 17) valence is 1. So the order is F < O < N.
Q14. Which of the following is the correct order of increasing first ionization enthalpy for the elements?
IntermediateB · Na < Al < Mg
Ionization enthalpy increases across a period, but there is a dip at Al because it has a single p electron, which is easier to remove than the paired s electron in Mg. So the order is Na < Al < Mg.
Q15. Which of the following is a diagonal relationship in the periodic table?
AdvancedB · Li and Mg
A diagonal relationship is observed between Li-Mg, Be-Al, and B-Si. The question asks for one, so Li and Mg is correct.
Q16. Which of the following is the correct order of first ionization enthalpy for the elements B, C, N, and O?
AdvancedD · B < C < O < N
Ionization enthalpy generally increases across a period, but there is a dip at O due to the extra stability of half-filled p orbitals in N. So the order is B < C < O < N.
Q17. Which of the following is the correct order of increasing atomic size for the ions?
AdvancedA · Al3+ < Mg2+ < Na+
Cations are smaller than their parent atoms. Among isoelectronic ions, the one with the highest positive charge has the smallest radius. So Al3+ < Mg2+ < Na+.
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