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Predict the Formula of the Ionic Compound from the Electronic Configuration

The electronic configuration of two elements A and B are -

A- 1s2 2s2 2p6 3s2 3p6 4s2

B- 1s2 2s2 2p6 3s2 3p5

What is the formula of the ionic compound formed between these elements?

Periodic_table_curlyarrows

 Step 1: Identify the element

Element A

A has a valence shell configuration of 2. Therefore, A belongs to the Group 2 of the periodic table.

A- 1s2 2s2 2p6 3s2 3p6 4s2

Group 2 elements are metals. Metals have low ionization enthalpy; they can easily lose electrons to attain the nearest stable, inert gas configuration. Group 2 elements can therefore lose two electrons to attain stability.

The principal quantum number of the outermost shell of element A is 4; therefore, the element belongs to the 4th period (row) of the periodic table.

Element A belonging to Group 2 and period 4, is Calcium (Ca).

Element B

B belongs to group 7 based on the valence shell electronic configuration of 7.

B- 1s2 2s2 2p6 3s2 3p5

The Group 7 elements are halogens. The halogens are less by one electron from attaining the stable inert gas configuration. Therefore, halogens have high negative electron gain enthalpy values and attain electrons easily.

The principal quantum number of the outermost valence shell of element B is 3; therefore, the element belongs to the 3rd period (row) of the periodic table.

The element B from the Group 7 and period 3 is Chlorine (Cl).

 Step 2: Predicting the Stoichiometry

The Group 2 Calcium (Ca) atom can easily lose two electrons, therefore,

 

Ca → Ca2+ + 2e-

 

One Cl atom can only pick one electron; therefore, the two electrons are accepted by 2 Cl atoms to give 2Cl- anions.

2Cl + 2e- → 2Cl-

 Net Reaction:

Ca2+  +   2 Cl-  → CaCl2

One Ca atom, and two Cl atoms form the compound Calcium Chloride (CaCl2).

Criss-cross (cross-multiplication) method to deduce the Molecular Formula

The simplest method is to employ the criss-cross method.

The valency of Ca is 1, and the one Ca atom comfortably loses two electrons to form Ca 2+ cation.

The valency of Cl is 1, and one Cl atom can accept one electron to form one Cl- anion. However, one Ca2+ cation requires 2 Cl atoms as 2Cl- to balance the charges and form a neutral compound.  

By criss-crossing the numerical value of charges and using it as a subscript, the correct ratio of the ions is obtained to conclude the formula of AB2 as  CaCl2.

Criss-cross method deduce structure Ab2

The sign of the charges in the subscript is ignored while writing the molecular formula.

 


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Introductory Organic Chemistry Course covers the fundamentals of organic chemistry in 13 detailed chapters –

  • Atoms

  • Bonding in Atoms

  • Covalent Bond 

  • Electronic Displacements in a Covalent Bond 

  • Common Reaction Types 

  • Drawing Organic Structures 

  • Functional Groups 

  • Structural Isomerism 

  • Intermolecular Forces 

  • Physical Properties 

  • Fundamentals of Organic Reactions 

  • Reactive Intermediates 

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What is Organic Chemistry?

  • Introduction
  • Elements of a Chemical Reaction
  • Components of a Chemical Reaction

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Atom

  • Size of an atom- The world belongs to the tiniest!
  • Power of Protons
  • Mass Number
  • Average Atomic Mass
  • Molecule and Molecular Mass
  • The Electrons- An Atom’s Reactive Component
  • Atomic Orbitals- s, p, d, f
  • Filing of Atomic Orbitals and Writing Electronic Configuration
  • Valence and Core Electrons- How to Determine

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Covalent Bond

  • Theories on Covalent Bond Formation
  • Valence Bond Theory- Introduction and Covalent Bond Formation
  • Valence Bond Theory- Types of Orbital Overlap Forming Covalent Bonds
  • Applications, Limitations, and Extensions of Valence Bond Theory
  • Hybridization- Introduction and Types
  • sp3 Hybridization of Carbon, Nitrogen, and Oxygen
  • sp2 Hybridization of Carbon, Carbocation, Nitrogen, and Oxygen
  • sp Hybridization of Carbon and Nitrogen
  • Shortcut to Determine Hybridization
  • VSEPR Theory- Introduction
  • Difference between Electron Pair Geometry and Molecular Structure
  • Finding Electron Pair Geometry and Related Shape
  • Predicting Electron-Pair Geometry and Molecular Structure Guideline
  • Predicting Electron pair geometry and Molecular structure - Examples
  • Finding Electron-Pair Geometry and Shape in Multicentre Molecules
  • Drawbacks of VSEPR Theory
  • Covalent bond Characteristics- Bond length
  • Factors affecting Bond Length
  • How does Electron delocalization (Resonance) affect the Bond length?
  • Covalent bond Characteristics- Bond Angle
  • Factors affecting Bond Angle
  • Covalent bond Characteristics- Bond Order
  • How Bond Order Corresponds to the Bond Strength and Bond Length
  • Solved Examples of Bond Order Calculations
  • Covalent Bond Rotation
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  • Covalent Bond Properties -Physical State, Melting and Boiling Points, Electrical Conductivity, Solubility, Isomerism, Non-ionic Reactions Rate, Crystal structure

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Electronic Displacement in a Covalent Bond

  • Electronegativity- Introduction
  • Factors Affecting Electronegativity- Atomic number, Atomic size, Shielding effect
  • Factors Affecting Electronegativity-s-orbitals, Oxidation state, Group electronegativity
  • Application of Electronegativity in Organic Chemistry
  • Physical Properties Affected by Electronegativity
  • Inductive effect- Introduction, Types, Classification, and Representation
  • Factors Affecting Inductive Effect- Electronegativity
  • Factors Affecting Inductive Effect- Bonding Order and Charge
  • Factors Affecting Inductive Effect- Bonding Position 
  • Application of Inductive Effect- Acidity Enhancement and Stabilization of the counter ion due to -I effect 
  • Application of Inductive Effect-Basicity enhancement and stabilization of the counter ion due to +I effect
  • Application of Inductive Effect-Stability of the Transition States
  • Application of Inductive Effect-Elevated Physical Properties of Polar Compounds
  • Is the Inductive Effect the same as Electronegativity?
  • Resonance- Introduction and Electron Delocalization 
  • Partial Double Bond Character and Resonance Hybrid
  • Resonance Energy
  • Significance of Planarity and Conjugation in Resonance
  • p-orbital Electron Delocalization in Resonance
  • Sigma Electron Delocalization (Hyperconjugation)
  • Significance of Hyperconjugation
  • Resonance Effect and Types
  • Structure Drawing Rules of Resonance (Includes Summary)
  • Application of Resonance
  • Introduction to Covalent Bond Polarity and Dipole Moment
  • Molecular Dipole Moment
  • Lone Pair in Molecular Dipole Moment
  • Applications of Dipole Moment
  • Formal Charges- Introduction and Basics
  • How to Calculate Formal Charges (With Solved Examples)
  • Difference between Formal charges and Oxidation State

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Common Types of Reactions

  • Classification of common reactions based on mechanisms
  • Addition Reactions
  • Elimination Reactions (E1, E2, E1cb)
  • Substitutions (SN1, SN2, SNAr, Electrophilic, Nucleophilic)
  • Decomposition
  • Rearrangement
  • Oxidation-Reduction

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Drawing Organic Structures

  • Introduction
  • Kekulé
  • Condensed
  • Skeletal or Bond line
  • Polygon formula
  • Lewis Structures- What are Lewis structures and How to Draw
  • Rules to Draw Lewis structures- With Solved Examples
  • Lewis structures- Solved Examples, Neutral molecules, Anions, and Cations
  • Limitation of Lewis structures
  • 3D structure representation- Dash and Wedge line
  • Molecular models for organic structure representation- Stick model, Ball-stick, and Space-filling
  • Molecular Formula

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Functional Groups in Organic Chemistry

  • What are functional groups? 
  • Chemical and Physical Properties affected by the Functional Groups
  • Identifying Functional Groups by name and structure
  • Functional Group Categorization- Exclusively Carbon-containing Functional Groups
  • Functional Group Categorization- Functional Groups with Carbon-Heteroatom Single Bond
  • Functional Group Categorization- Functional Groups with Carbon-Heteroatom Multiple Bonds
  • Rules for IUPAC nomenclature of Polyfunctional Compounds
  • Examples of polyfunctional compounds named according to the priority order
  • Examples of reactions wherein the functional group undergoes transformations

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Structural Isomerism

  • Introduction
  • Chain Isomerism
  • Position Isomerism
  • Functional Isomerism
  • Tautomerism
  • Metamerism
  • Ring-Chain Isomerism

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Intermolecular Forces

  • Ion-Dipole Interactions-Introduction and Occurrence
  • Factors Affecting the Ion-Dipole Strength
  • Importance of Ion-Dipole Interactions
  • Ion-Induced Dipole- Introduction, Strength and Occurrence
  • Factors Affecting the Strength of Ion-Induced Dipole Interactions
  • Ion-Induce Dipole Interactions in Polar Molecules
  • Vander Waals Forces -Introduction
  • Examples of Vander Waals' forces
  • Vander Waals Debye (Polar-Nonpolar) Interactions
  • Factors affecting the Strength of Debye Forces
  • Vander Waals Keesom Force- Introduction, Occurrence and Strength
  • Vander Waals London Forces- Introduction, Occurrence, And Importance
  • Factors Affecting the Strength of London Dispersion Forces- Atomic size and Shape
  • Introduction, Occurrence and Donor, Acceptors of Hydrogen Bond
  • Hydrogen bond Strength, Significance and Types
  • Factors Affecting Hydrogen Bond Strength
  • Impact of Hydrogen bonding on Physical Properties- Melting and boiling point, Solubility, and State
  • Calculation of the Number of Hydrogen Bonds and Hydrogen bond Detection

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Physical Properties

  • Physical Properties- Introduction, Role of Intermolecular Forces
  • Physical State Change-Melting Point
  • Role of Symmetry, Role of Carbon numbers, Role of Geometry
  • Physical State Change-Boiling Point
  • Intermolecular Forces and their Effect on the Boiling Point, Role of Molecular Weight (Size), Molecular Shape, Polarity
  • Boiling Point of Special Compounds- Amino acids, Carbohydrates, Fluoro compounds
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  • Density

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Fundamentals of Organic Reactions

  • Types of Arrows Used in Chemistry
  • Curved Arrows in Organic Chemistry- with Examples
  • Electrophiles- Introduction, Identification and Reaction
  • Formation and Classification of Electrophiles- Neutral and Charged 
  • Difference between Electrophiles and Lewis Acids
  • Nucleophile- Identification and Role in a Reaction
  • Types of Nucleophiles- Lone Pair
  • Types of Nucleophiles- Pie Bond
  • Types of Nucleophiles- Sigma Bond
  • Periodic Trend and Order in Nucleophilicity
  • Introduction to Reactions Involving Nucleophiles
  • Nucleophile Reactions- Aliphatic Displacement type - SN1, SN2
  • Nucleophile Reactions- Acyl Displacement type
  • Nucleophile reactions- Aromatic Displacement type- Electrophilic, Nucleophilic
  • Addition Reactions- Electrophilic, Nucleophilic, and Acyl
  • Ambident Nucleophiles- Introduction and Formation 
  • Ambident Nucleophile - Nature of the Substrate
  • Ambident Nucleophile- Influence of the Positive Counter Ions
  • Ambident Nucleophile- Effect of Solvent 
  • Lone Pair - Introduction and Formation
  • Physical Properties Affected by the Lone Pair- Shape and Bond Angle
  • Physical Properties Affected by the Lone Pair- Hydrogen Bonding
  • Physical Properties Affected by the Lone Pair- Polarity and Dipole Moment
  • Chemical property affected by the Lone pair- Nucleophilicity
  • Leaving Group- Introduction and Nature
  • Good and Bad Leaving Group
  • Factors Determining Stability of the Leaving Groups- Electronegativity, Size, Resonance Stability
  • Using pKa as a Measure of Leaving Group Ability
  • Leaving Groups in Displacement Reactions
  • Leaving Groups in Elimination Reactions

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Reactive Intermediates

  • Carbocation- Introduction, Nature, and Types
  • Formation of Carbocation
  • Stability of Carbocations- Inductive, Resonance, and Hyperconjugation
  • Other Structural Features Increasing Carbocation Stability
  • Structural Feature Decreasing Carbocation Stability
  • Fate of the Carbocation
  • General Carbocation Formation Reactions
  • Carbanion- Introduction, Nature, and Types
  • Formation of Carbanions
  • Carbanion Stabilization
  • Ease of Formation of Carbanion -Acidic proton
  • Fate of the Carbanion
  • Free Radical- Introduction and Types of Carbon-Centred Radicals
  • Structure of Carbon-Centred Free Radical
  • Formation of Radicals
  • Stability of the Carbon-Centred Radicals
  • Other Structural Feature Increasing Free Radical Stability
  • Comparing Free Radical Stability using Dissociation energies (D-H) 
  • Fate of Free Radicals
  • Common Reactions Involving Carbon-Free Radicals

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