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SME Chemistry Topic 14 Notes
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SME Chemistry Topic 14 Notes
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H e a d t o s a v e m y e x a m s . c o . u k f o r m o r e a w e s o m e r e s o u r c e sPage 1 of 33
© 2 0 1 5 − 2 0 2 3 S a v e M y E x a m s , L t d . · R e v i s i o n N o t e s , T o p i c Q u e s t i o n s , P a s t P a p e r sIB Chemistry DP
14. HL Chemical Bonding & Structure
CONTENTS
14.1 More Structures & Shapes
14.1.1 Covalent Bonds
14.1.2 More Lewis Structures
14.1.3 Further VSEPR Theory
14.1.4 Formal Charge
14.2 Further Aspects of Bonding
14.2.1 Delocalisation & Resonance
14.2.2 Ozone Revisited
14.2.3 Hybrid OrbitalsYOUR NOTES H e a d t o s a v e m y e x a m s . c o . u k f o r m o r e a w e s o m e r e s o u r c e s
Page 2 of 33
© 2 0 1 5 − 2 0 2 3 S a v e M y E x a m s , L t d . · R e v i s i o n N o t e s , T o p i c Q u e s t i o n s , P a s t P a p e r sSigma Bonds
Bond overlap in covalent bonds
A single covalentbond is formed when two nonmetals combine
Each atom that combines has an atomicorbital containing a single unpaired electron
When a covalent bond is formed, the atomic orbitals overlap to form a combined
orbital containing two electrons
This new orbital is called the molecular orbital
The greater the atomic orbital overlap, the stronger the bond
Sigma ( σ) bonds are formed from the head-on/ end-to-end overlap of atomic orbitals
The electron density is concentrated between the two nuclei
S orbitals overlap this way as well as p to p, and s with p orbitals
Sigma orbitals can be formed from the end-on overlap of s orbitals
Hydrogen fluoride has sigma bonds between s and p orbitals
Fluorine has sigma bonds between p orbitals
The electron density in a σ bond is symmetrical about a line joining the nuclei of the atoms forming the
bond
14.1 More Structures & Shapes
14.1.1 Covalent BondsYOUR NOTES H e a d t o s a v e m y e x a m s . c o . u k f o r m o r e a w e s o m e r e s o u r c e s
Page 3 of 33
© 2 0 1 5 − 2 0 2 3 S a v e M y E x a m s , L t d . · R e v i s i o n N o t e s , T o p i c Q u e s t i o n s , P a s t P a p e r sThe pair of electrons is found between the nuclei of the two atoms
The electrostatic attraction between the electrons and nuclei bonds the atoms to each
otherYOUR NOTES H e a d t o s a v e m y e x a m s . c o . u k f o r m o r e a w e s o m e r e s o u r c e s
Page 4 of 33
© 2 0 1 5 − 2 0 2 3 S a v e M y E x a m s , L t d . · R e v i s i o n N o t e s , T o p i c Q u e s t i o n s , P a s t P a p e r sPi Bonds
π bonds
Pi (π) bonds are formed from the sidewaysoverlap of adjacent p orbitals
The two lobes that make up the π bond lie aboveandbelowtheplane of the σ bond
This maximises overlap of the p orbitals
A single π bond is drawn as two electron clouds one arising from each lobe of the p orbitals
The two clouds of electrons in a π bond represent one bond containing two electrons
π orbitals are formed by the end-on overlap of p orbitals
Examples of sigma & pi bonds
Hydrogen
The hydrogen atom has only one s orbital
The s orbitals of the two hydrogen atoms will overlap to form a σ bond
Direct overlap of the 1s orbitals of the hydrogen atoms results in the formation of a σ bond
Ethene
Each carbon atom uses three of its four electrons to form σ bonds
Two σ bonds are formed with the hydrogen atoms
One σ bond is formed with the other carbon atom
The fourth electron from each carbon atom occupies a p orbital which
overlaps sideways with another p orbital on the other carbon atom to form a π bond
This means that the C-C is a double bond: one σ and one π bondYOUR NOTES
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