This chapter discusses the system of classifying elements based on their properties and the periodicity observed in these properties. It is vital for understanding chemical behavior and the organization of the periodic table.
Classification of Elements and Periodicity in Properties – Formula & Equation Sheet
Essential formulas and equations from Chemistry Part - I, tailored for Class 11 in Chemistry.
This one-pager compiles key formulas and equations from the Classification of Elements and Periodicity in Properties chapter of Chemistry Part - I. Ideal for exam prep, quick reference, and solving time-bound numerical problems accurately.
Key concepts & formulas
Essential formulas, key terms, and important concepts for quick reference and revision.
Formulas
Z = N + P
Z (atomic number) is the total number of protons; N is the number of neutrons; P is the number of protons. This represents the basic structure of an atom.
E = −K/Z^2
E represents the energy of an electron in the nth orbit. K is a constant and Z is the atomic number. This formula is derived from the Bohr model of the atom.
IE = ΔH (X(g) → X+(g) + e−)
Ionization Energy (IE) is the energy change (ΔH) when an electron is removed from a gaseous atom X. It shows the energy required to form a cation.
ΔH (X(g) + e− → X−(g))
This equation represents the electron gain enthalpy (ΔH) of element X when it gains an electron to form an anion.
AR decreases across a period
Atomic radius (AR) decreases from left to right across a period due to increasing nuclear charge, attracting electrons closer to the nucleus.
AR increases down a group
Atomic radius increases down a group due to additional electron shells being added, increasing the distance from the nucleus.
ΔEg < 0 for non-metals
The electron gain enthalpy (ΔEg) is generally negative for non-metals as they release energy when gaining electrons.
ΔEg positive for noble gases
For noble gases, electron gain enthalpy is positive since they have complete valence shells and do not favor adding electrons.
Electronegativity increases across a period
Electronegativity tends to increase from left to right across a period as a result of increased nuclear attraction on bonding electrons.
Electronegativity decreases down a group
Electronegativity decreases down a group due to increased atomic radius and shielding effect, making it harder for the nucleus to attract bonding electrons.
Equations
X(g) → X+(g) + e−
This represents the first ionization energy, where an electron is removed from a neutral gaseous atom.
X(g) + e− → X−(g)
This equation represents the process of an atom gaining an electron, leading to the formation of an anion.
Na + Cl2 → NaCl
This reaction illustrates the formation of ionic compound sodium chloride from sodium and chlorine.
2H2 + O2 → 2H2O
This shows the reaction between hydrogen and oxygen that forms water, demonstrating the reactivity of elements.
Na2O + H2O → 2NaOH
This reaction demonstrates that sodium oxide reacts with water to form sodium hydroxide, a strong base.
Cl2O7 + H2O → 2HClO4
This equation illustrates that dichlorine heptoxide reacts with water forming perchloric acid, an acidic oxide.
X-2 + e− → X−
When X gains an electron, this depicts the reduction process resulting in the formation of a negatively charged ion.
E = mc²
This famous formula defines the relationship between mass (m) and energy (E), illustrating the concept of mass-energy equivalence.
E (in kJ/mol) = IE + ΔEg
This equation relates ionization energy and electron gain enthalpy, indicating the energy balance for reactions involving electrons.
Z = A + E
This equation relates the atomic number (Z), mass number (A), and number of neutrons (E) in an atom.
This chapter introduces basic concepts of chemistry, including the study of matter, its properties, and its transformations. Understanding these concepts is crucial for students as they lay the foundation for further studies in chemistry.
Start chapterThis chapter introduces the structure of atoms, focusing on sub-atomic particles, atomic models, and quantum mechanics, which are fundamental to understanding chemistry.
Start chapterThis chapter explains the fundamental concepts of chemical bonding and molecular structure, focusing on theories that describe how atoms combine to form molecules, which is essential for understanding chemical reactions.
Start chapterThis chapter introduces thermodynamics, the study of energy changes in chemical reactions and processes. Understanding thermodynamics is essential for predicting how and why reactions occur.
Start chapterThis chapter covers the principles of chemical equilibrium, including its significance in biological and environmental processes. It emphasizes understanding dynamic equilibrium, the equilibrium constant, and the factors affecting equilibrium states.
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