CHEMICAL BONDING SUTHERLAND HIGH SCHOOL K. FALING EDITED: R. BASSON GRADE 10 PHYSICAL SCIENCE TB. 103
HOW DOES BONDING WORK? The chemical reaction between elements leads to compounds, which have new physical and chemical properties. A bond is the force that holds atoms together to form molecules. This happens so that the millions of different substances found on earth can be formed. Intermolecular bonds/forces between MOLECULES Intramolecular bonds/forces between ATOMS There are ATTRACTIVE forces between the nucleus of one atom (+) and the electrons of the other atom and there are REPULISIVE forces between the electrons of different atoms. When the attractive force is GREATER than the REPULSIVE force that exists between them. Elements will bond with each other to become stable = full energy levels. Only valence electrons are involved in bonding. TB. 103
3 TYPES OF INTRAMOLECULAR BONDING 1. COVALENT BONDS - Between atoms of non-metals O O 2. IONIC BONDS - Between atoms of metals and non metals Na Cl 3. METALLIC BONDS - Between atoms of metals Cu Cu TB. 103
REPRESENTING BONDING Bonding is illustrated by using LEWIS DIAGRAMS. Requirements Only valence electrons are drawn. Electrons are represented as dots or crosses around the symbol of the element. VALENCE ELECTRONS? EXAMPLE GROUP NUMBER? TB. 103
IMPORTANT INFO ABOUT LEWIS DIAGRAMS VALENCE ELECTRONS ARE DRAWN. THEY ARE REPRESENTED AS DOTS BUT ALSO CONTAINS LINES TO REPRESENT SHARED PAIRS IN A CHEMICAL BOND. EXCESS ELECTRONS THAT FORM LONE PAIRS ARE REPRESENTED AS PAIRS OF DOTS, AND ARE PLACED NEXT TO THE ATOMS. EACH ELEMENT WILL GAIN, LOOSE OR SHARE ELECTRONS UNTIL THEY HAVE RECEIVED AN OCTET OF ELECTRONS = FULL VALENCE SHELL ELECTRON CONFIGURATION.
PRACTICE DRAW LEWIS DIAGRAMS FOR THE FOLLOWING STRUCTURES Ar Ca H Zn
HOMEWORK EXERCISE 8
BETWEEN NON-METAL ATOMS 1. COVALENT BONDS Single Double Triple ORBITALS WITH HALF-FILLED ORBITALS WILL OVERLAP AND ELECTRONS ARE SHARED SMALLEST PARTICLE IS A MOLECULE THE TYPE OF COVALENT BOND IS DETERMINED BY THE DIFFERENCE IN ELECTRONEGATIVITY NON-POLAR COVALENT - DIFFERENCE < 0.9 Attraction is shared equally POLAR COVALENT - 0.9 < DIFFERENCE < 1.7 One atom attracts the shared pair more than the other. IONIC - DIFFERENCE > 1.7 EXAMPLE: H 2 0 TB. 104
PRACTICE DRAW LEWIS DIAGRAMS FOR THE FOLLOWING BONDS Hydrogen H 2 Water H 2 0 Nitrogen N 2 TB. 104
IONIC BONDS OCCUR BETWEEN A METAL AND NON-METAL ATOMS INVOLVES THE TRANSFER OF ELECTRONS METALS TEND TO GIVE AWAY ELECTRONS AND BECOME POSITIVE IONS (CATIONS) AND THE NON- METALS TEND TO ACCEPT THE ELECTRONS AND BECOME NEGATIVE IONS (ANIONS) SO: METALS LOW IONISATION ENERGY AND NON-METALS: HIGH ELECTRON AFFINITY. THE CATIONS AND ANIONS ATTRACT EACH OTHER WITH STRONG ELECTROSTATIC OR COULOMBIC FORCES LARGE CRYSTAL LATTICES ARE FORMED THE SMALLEST PARTICLE MAKING UP AN IONIC CRYSTAL LATTICE IS AN ION EXAMPLES INCLUDE: NACl; KMNO 4 ; MGSO 4 ; CACO 3 TB. 106
DRAWING LEWIS DIAGRAMS THE IONIC BONDS Na Cl 2 TB. 106
METALLIC BONDS OCCUR BETWEEN METAL ATOMS THE ATOMIC NUCLEI WITH THE INNER ELECTRON SHELLS ARE TIGHTLY PACKED TOGETHER IN AN ORGANISED CRYSTAL STRUCTURE THE OUTERMOST ORBITALS OVERLAP THE VALENCE ELECTRONS ARE DELOCALISED AND CAN MOVE INTO ADJACENT ORBITALS OF NEARBY ATOMS. THE SMALLEST PARTICLE OF A METALLIC CRYSTAL IS A POSITIVE METAL ION EXAMPLE: PIECES OF ZN, FE, CU AND AG TB. 107
QUICK SUMMARY Property Ionic bond Covalent bond Smallest particle Ion Molecules Atom Metallic bond Types of elements Metals & non-metals Non-metals Metals How does bond occur? Electron transfer Sharing of electrons Positive atomic core with sea of delocalized electrons TB. 110
HOMEWORK EXERCISE 9
ALL MATTER IS MADE UP OF SMALL PARTICLES CALLED ATOMS A MOLECULE (NON-METALS) CONSISTS OF 2 OR MORE ATOMS THAT ARE BOUND TOGETHER BY STRONG ATTRACTIVE FORCES A CHEMICAL COMPOUND IS A GROUP OF TWO OR MORE ATOMS OF DIFFERENT TYPES THAT ARE HELD TOGETHER BY STRONG FORCES OR BONDS. THESE ATOMS ALWAYS BOND IN A SPECIFIC RATIO. TB. 111
MOLECULAR FORMULA The actual number and type of atoms in the compound. Example: 0 2 0 3 H 2 0 C 8 H 18 EMPIRICAL FORMULA The simplest ratio in which atoms combine. STRUCTUAL FORMULA Shows the arrangement of the atoms and bonds TB. 117
BALL AND STICK SPACE FILLING DIAGRAM LEWIS STRUCTURE TB. 118
HOMEWORK EXERCISE 10
TEST EXAMPLES
Molecules (molecular substances) are due to covalent bonding. Ionic substances are due to ionic bonding.
When the electrons of atoms are transferred from one atom to another atom to form positive and negative ions, the ions bond with ionic bonds and the resulting solid is called an ionic substance (or salt or ionic compound). As a general rule ionic substances are usually composed of both metallic elements (usually forming positive ions) and nonmetallic elements (usually forming negative ions) When metal atoms lose their outer electrons to form a lattice of regularly spaced positive ions and the outer electrons form a delocalized pool of electrons that surround the positive ions, the atoms are bonded by metallic bonding and the resulting collection of atoms is called a metal Give examples of molecules based on the above description e.g. Covalent molecular structures consist of separate molecules: oxygen, water, petrol, CO2, S8, C60 (buckminsterfullerene or buckyballs)