Chapter 6: Chemical Bonding Section 1: Introduction to Chemical Bonding

 BELL RINGER: 11/29  Imagine getting onto a crowded elevator. What happens as more and more people get onto the elevator? How does it make you feel? How do you think the people around you feel? (Also – think about the feeling you get when you’re on a crowded train) Section 1: Introduction to Chemical Bonding

 Imagine getting onto a crowded elevator. As people squeeze into the confined space, they come in contact with each other. Many people will experience a sense of being too close together.  When atoms get close enough, their outer electrons repel each other. At the same time, however, each atom’s outer electrons are strongly attracted to the nuclei of the surrounding atoms. Section 1: Introduction to Chemical Bonding

 Objectives:  Describe how scientific inferences are drawn from scientific observations and provide examples from the content being studied  Distinguish between bonding forces holding compounds together and other attractive forces, including hydrogen bonding and van der Waals forces

Section 1: Introduction to Chemical Bonding  Atoms seldom exist as independent particles in nature.  Oxygen you breathe and water you drink are combinations of atoms that are held together by chemical bonds.  Chemical Bond – a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.  Chemicals are bonded together because as individuals particles they are at relatively high potential energy  Nature wants potential energy minimalized Visual Concept

Types of Chemical Bonding  When atoms bond, their valence electrons (electrons in the s & p orbitals of the HIGHEST energy level) are redistributed in ways that make the atom MORE stable. 1. Ionic bonding – chemical bonding that results from the electrical attraction between cations (positive ions) and anions (negative ions)  In a purely Ionic Bond – atoms completely give up electrons to other atoms Visual Concept

Types of Chemical Bonding 2. Covalent bonding – results from the sharing of electron pairs between atoms  In a purely covalent bond – the shared electrons are “owned” equally by the two bonded atoms Visual Concept

Types of Chemical Bonding – Ionic or Covalent?  Bonding is rarely purely covalent or purely ionic  Usually the bonds fall somewhere in between depending on how strongly the atoms of each element attract electrons Remember: electronegativity – measure of an atom’s ability to attract electrons  The degree to which the bonding is covalent (sharing) or ionic (giving up electrons) is determined by:  Calculating the difference in the elements’ electronegativities Visual Concept

Types of Chemical Bonding – Ionic or Covalent?  Examples:  What is the difference in electronegativity of Fluorine (F) and Cesium (Cs)?  4.0 – 0.7 = 3.3

Types of Chemical Bonding – Ionic or Covalent?  Sample Problem A Determine bonding between sulfur, S (2.5), and the following elements: hydrogen, H (2.1); cesium, Cs (.7); and chlorine, Cl (3.0). In each pair, which atom will be more negative?

Types of Chemical Bonding – Ionic or Covalent?  Sample Problem A Solution The electronegativity of sulfur is 2.5. The electronegativities of hydrogen, cesium, and chlorine are 2.1, 0.7, and 3.0, respectively. In each pair, the atom with the larger electronegativity will be the more-negative atom. Bonding betweenElectroneg.Bond type: More sulfur and:difference:negative: hydrogen2.5 – 2.1 = 0.4polar-covalentsulfur cesium2.5 – 0.7 = 1.8ionicsulfur chlorine3.0 – 2.5 = 0.5polar-covalentchlorine