3.1.4
Periodic Trends - Electronegativity & Affinity
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Trends in Electronegativity
Electronegativity is a measure of the tendency of an atom to attract electrons (or electron density) towards itself.
Electronegativity
- In a bond between two unlike atoms, one atom will have a stronger attraction to the electron pair than the other.
- This means the electron pair will not be at the center of the bond.
- This causes the buildup of a partial charge on one atom.
- This is written as δ±
- The ability of an atom to attract the electron pair is called electronegativity.
Pauling electronegativities
- The values of electronegativity can be measured on several different scales.
- One example is the Pauling scale (named after Linus Pauling, its inventor).
- The most electronegative element is fluorine, with a value of 4.0.
- Other strongly electronegative elements are oxygen (3.4), chlorine (3.2), nitrogen (3.0)
- Carbon has an electronegativity of 2.5 and hydrogen has an electronegativity of 2.2.
Periodic trends
- In general, electronegativity increases from left to right across a period in the periodic table and decreases down a group.
- Thus, the nonmetals, which lie in the upper right, tend to have the highest electronegativities.
- As you may recall, fluorine the most electronegative element of all.
- Metals tend to be less electronegative elements, and the group 1 metals have the lowest electronegativities.
Noble gases
- Note that noble gases are excluded from this figure because these atoms usually do not share electrons with others atoms since they have a full valence shell.
- While noble gas compounds such as XeO2 do exist, they can only be formed under extreme conditions, and thus they do not fit neatly into the general model of electronegativity.
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Polarity
- The most electronegative atom in a bond will develop a partial negative charge (δ-) and vice versa.
- This charge difference is called a permanent dipole.
- A good example of a polar bond is the HCl molecule.
- A good example of a non-polar bond is the C-H bond.
- The electronegativities of hydrogen and carbon are very similar, so the bond is not polar.
Electron Affinity
The electron affinity of an element is the energy released or absorbed when an isolated gas-phase atom acquires an electron, measured in kJ/mol.
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Electron affinity vs electronegativity
- The electron affinity of an element is a measurable physical quantity.
- Electron affinity is the energy released or absorbed when an isolated gas-phase atom acquires an electron, measured in kJ/mol.
- Electronegativity describes how tightly an atom attracts electrons in a bond.
- It is a dimensionless quantity that is calculated by comparing the amounts of energy required to break different types of bonds.
Trends in electron affinity
- Electron affinity increases from left to right across a period in the periodic table and decreases down a group.
Trends - down a group
- As you go down a group, there is an increased number of electron shells.
- The greater the number of electrons between the nucleus and the outer electrons, the lower the effective nuclear charge.
- This is because the positive charge felt by the electron is reduced by the electrons in between.
- This means that the greater the number of electrons, the lower the electron affinity as it is more difficult to gain an electron.
Trends - across a period
- As you go across a period, the number of protons increases. This means nuclear charge increases across a period.
- As you go across a period, electrons are added to the same shell. For example, all elements in the second period have two electron shells.
- An increased nuclear charge across a period means a greater attraction between the nucleus and the electron to be gained.
- This means electron affinty increases across a period.
1Structure - Models of the Particulate of Matter
1.1Introduction to the Particulate Model of Matter
1.2The Nuclear Atom
1.3Electron Configuration
1.4Counting Particles by Mass: The Mole
1.6Elements, Compounds & Mixtures
1.7States of Matter & Changes of State
1.8Reacting Masses &. Volumes
1.9Solutions
2Structure - Models of Bonding & Structure
2.1The Ionic Model
2.2The Covalent Model
2.3Covalent Structures
2.4The Metallic Model
2.5From Models to Materials
2.6Valence Electrons & Ionic Compounds
2.7Molecular Shape
3Structure - Classification of Matter
3.1The Periodic Table: Classification of Elements
3.2Periodic Trends
3.3Group 1 Alkali Metals
3.4Halogens
3.5Noble gases, group 18
3.6Functional Groups: Classification of Organic
3.7Functional Group Chemistry
3.8Alkanes
3.9Alcohols
4Reactivity - What Drives Chemical Reaction?
4.1Endothermic & Exothermic Reactions
4.2Enthalpy of Reaction, Formation, & Hess' Law
5Reactivity - How Much, How Fast & How Far?
5.1Kinetics
5.2Rates of Reaction
5.3Stoichometry
5.4Le Châtelier’s Principle
5.5Introduction to Equilibrium
5.6Equilibrium Constant
5.7Reaction Quotient & Equilibrium Constant
6Reactivity - The Mechanisms of Chemical Change
6.1Proton Transfer Reactions
6.2The pH Scale
6.3Strong & Weak Acids and Bases
6.4Acid Deposition
6.5Types of Organic Reactions
6.6Oxidation & Reduction
6.7Electrochemical Cells
6.9Acid-Base Titrations
6.9.1Titration Calculation Weak Acid & Strong Base6.9.2Titration Experimental Detail6.9.3Extended Response - Titration6.9.4Titration Calculations6.9.5Titration Curves6.9.6Titration Calculation Strong Acid & Weak Base6.9.7IB Multiple Choice - Titrations6.9.8Polyprotic Acids6.9.9Titration Calculations Strong Acid & Strong Base6.9.10Titrations Curves 2
7Measurement, Data Processing & Analysis
7.1Uncertainties & Errors in Measurements & Results
7.2Graphical Techniques
7.3Spectroscopic Identification of Organic Compounds
7.4Infrared Spectroscpy
Jump to other topics
1Structure - Models of the Particulate of Matter
1.1Introduction to the Particulate Model of Matter
1.2The Nuclear Atom
1.3Electron Configuration
1.4Counting Particles by Mass: The Mole
1.6Elements, Compounds & Mixtures
1.7States of Matter & Changes of State
1.8Reacting Masses &. Volumes
1.9Solutions
2Structure - Models of Bonding & Structure
2.1The Ionic Model
2.2The Covalent Model
2.3Covalent Structures
2.4The Metallic Model
2.5From Models to Materials
2.6Valence Electrons & Ionic Compounds
2.7Molecular Shape
3Structure - Classification of Matter
3.1The Periodic Table: Classification of Elements
3.2Periodic Trends
3.3Group 1 Alkali Metals
3.4Halogens
3.5Noble gases, group 18
3.6Functional Groups: Classification of Organic
3.7Functional Group Chemistry
3.8Alkanes
3.9Alcohols
4Reactivity - What Drives Chemical Reaction?
4.1Endothermic & Exothermic Reactions
4.2Enthalpy of Reaction, Formation, & Hess' Law
5Reactivity - How Much, How Fast & How Far?
5.1Kinetics
5.2Rates of Reaction
5.3Stoichometry
5.4Le Châtelier’s Principle
5.5Introduction to Equilibrium
5.6Equilibrium Constant
5.7Reaction Quotient & Equilibrium Constant
6Reactivity - The Mechanisms of Chemical Change
6.1Proton Transfer Reactions
6.2The pH Scale
6.3Strong & Weak Acids and Bases
6.4Acid Deposition
6.5Types of Organic Reactions
6.6Oxidation & Reduction
6.7Electrochemical Cells
6.9Acid-Base Titrations
6.9.1Titration Calculation Weak Acid & Strong Base6.9.2Titration Experimental Detail6.9.3Extended Response - Titration6.9.4Titration Calculations6.9.5Titration Curves6.9.6Titration Calculation Strong Acid & Weak Base6.9.7IB Multiple Choice - Titrations6.9.8Polyprotic Acids6.9.9Titration Calculations Strong Acid & Strong Base6.9.10Titrations Curves 2
7Measurement, Data Processing & Analysis
7.1Uncertainties & Errors in Measurements & Results
7.2Graphical Techniques
7.3Spectroscopic Identification of Organic Compounds
7.4Infrared Spectroscpy
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