Thursday October 25, 2012 (Orbital Notation; Introduction to Chemical Bonding)

Determine which elements are represented by each of the following notations: 1s 2, 2s 2, 2p 3 Uranium-238 nitrogen 1s 2, 2s 2, 2p 6, 3s 2, 3p 6, 4s 2 calcium 1s 2, 2s 2, 2p 5 fluorine carbon-12 1s2s2px2py2pz3s3px3py3pz chlorine

Use Lewis Dot Structures to show how water is formed. Do the same for table salt, NaCl.

Announcements

Assignment Currently Open Summative or Formative? Date IssuedDate Due Date Into GradeSpeed Final Day QUIZ 6S310/5 10/26 QUIZ 7S410/12 10/26 Pop Quiz – The Periodic Table and the Periodic Law F410/16 QUIZ 8S510/19 10/2211/2 WS – Valence Electrons and Electron Configuration F510/2210/26 WS – Average Atomic Mass F610/2210/26 WS – Electron Dot Notation F710/2310/26 WS – Arrangement of Electrons in Atoms F810/2410/26

Example : Neon 10 protons, 10 neutrons, 10 electrons 1s 2, 2s 2, 2p 6 Our fourth notation, Orbital Notation, is based upon the fact that electrons settle into pairs in what’s called an “orbital.” Think of an orbital as a shoebox and the two electrons in the orbital as shoes. In this notation, electrons are represented as arrows and p sub-levels are divided into three orbitals holding 2 electrons each. 1s2s2px 2py 2pz

Chemical Bonding

Atoms seldom exist as independent particles in nature. A chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.

Chemical Bonding Why are most atoms chemically bonded to each other? – as independent particles, they are at relatively high potential energy. Nature, however, favors arrangements in which potential energy is minimized.

Chemical Bonding This means that most atoms are less stable existing by themselves than when they are combined. By bonding with each other, atoms decrease in potential energy, thereby creating more stable arrangements of matter.

Types of Chemical Bonds Chemical bonds are formed to stabilize atoms by reducing the single atoms’ potential energy. When atoms bond, their valence electrons are redistributed in ways that make the atoms more stable. The way in which the electrons are redistributed determines the type of bonding.

Types of Chemical Bonds Main block (s and p) metals (and H) tend to lose electrons to form + ions (cations), while non- metals tend to gain electrons to form – ions (anions). Chemical bonding that results from the attraction between large numbers of cations and anions is called ionic bonding. When atoms either lose or gain electrons in order to bond, it is referred to as a transfer of electrons. In order to bond, these atoms lose electrons and form + cations In order to bond, these atoms gain electrons and form - anions

Ionic Bonding Atom A represents a metal element that has lost electrons to form + cations. Atom B represents a non-metal element that has gained electrons to form - anions. The result is a cluster of ions of both types that are stuck together because of their opposite electromagnetic charges.

Types of Chemical Bonds Chemical bonding that results from the sharing of electron pairs between two atoms is called covalent bonding. The non-metal and metalloid elements indicated here share electrons when they bond with each other. When two or more non- metals or metalloids bond, atoms don’t lose or gain electrons; rather they share pairs of valence electrons.

Covalent Bonding Atom C represents a non-metal or metalloid element. Atom D represents a different non- metal or metalloid element. The result is two atoms held together by the sharing of the pair(s) of valence electrons. This unit is called a molecule.

Ionic or Covalent? What determines if atoms of different elements will bond ionically or covalently? The electronegativity difference between the two bonding elements makes the determination. Bonding between atoms of different elements is rarely purely ionic or covalent, but falls somewhere between based upon these electronegativity differences. By calculating the difference in the electronegativity values of the involved atoms, you can predict the degree to which the bond is likely to be ionic or covalent.

Example 1: atoms of sodium and chlorine are bonding. Sodium’s electronegativity is 0.9. Chlorine’s is 3.0. If we take the difference we get: 3.0 – 0.9 = 2.1

Consult the Bonding Character Chart and see where the difference falls. 2.1 This falls in the Ionic range; therefore, sodium and chlorine will bond ionically.

Example 2: atoms of hydrogen and oxygen are bonding. Hydrogen’s electronegativity is 2.1. Oxygen’s is 3.5. If we take the difference we get: 3.5 – 2.1 = 1.4

Consult the Bonding Character Chart and see where the difference falls. 1.4 This falls in the Polar-covalent range; therefore, hydrogen and oxygen will bond covalently.

Example 3: two atoms of nitrogen are bonding. Nitrogen’s electronegativity is 3.0. If we take the difference we get: 3.0 – 3.0 = 0

Consult the Bonding Character Chart and see where the difference falls. 0 This falls in the Nonpolar-covalent range; therefore, two atoms of nitrogen will bond covalently.

Introduction to Chemical Bonding Worksheet