CHEMICAL BONDING IN MATTER Text p ) Chemical Bonds are attractive electrostatic forces that hold atoms or ions together in a substance.

Transcription

1 CHEMICAL BONDING IN MATTER Text p ) Chemical Bonds are attractive electrostatic forces that hold atoms or ions together in a substance. Bohr's Model of the Atom protons and neutrons are located in the nucleus electrons are located in orbits or specific energy levels outside the nucleus. Bohr's Energy Level Diagrams Feb 2 11:41 AM 1

2 Quick Quiz! What subatomic particle determines an ion's charge? What are the maximum number of electrons in the first 3 energy levels? Where do we find the number of protons in an atom? What group of elements are stable and unreactive? Feb 5 8:47 PM 2

3 Draw bohr diagrams and energy level diagrams for the following atoms: sodium ion,magnesium, nitride ion and chlorine. Feb 2 1:55 PM 3

4 But these diagrams are HUGE! Can they help us show bonding? Feb 7 3:34 PM 4

5 Valence Energy Level is the outermost energy level of an atoms which contains electrons. Valence Electrons is the electrons in the highest occupied energy level of an atom. The number of valence electrons of an element (in Group A) has is equal to the group number in which it is found. Feb 2 11:45 AM 5

6 Lewis Structures or Electron Dot Diagrams When two atoms approach each other, it is their outermost energy levels (valence shells) that come in contact first. Gilbert N. Lewis: To show formation of chemical bonds we need only show valence electrons rather than all electrons as in Bohr Energy Level Diagrams Rules: 1) For each element, a) write down the symbol of the element. This represents the nucleus and inner energy level electrons. b) use the periodic table to determine the number of valence electrons for the atom. c) Place the dots (representing electrons) in four areas (orbitals) around the atom. DO NOT form pairs, until each of the four areas has at least one dot. Feb 2 11:45 AM 6

7 Lewis diagram for sulfur step 1: write the element symbol. step 2: place dots in orbitals one at a time. Feb 9 2:52 PM 7

8 Lone Pairs Bonding Electron and Bonding Capacity Lone Pairs (non bonding electrons) are electrons found as pairs in filled valence orbitals of an atom. They are rarely involved in bond Bonding Electron (or 'unpaired electron') is a single electron in a valence orbital of an atom. Bonding electrons are always involved bonding. Bonding Capacity is the maximum number of bonds an atom can form. It equals the number of bonding electrons in the atoms. Apr 4 9:26 AM 8

9 Symbol Dot Diagram # Lone Pairs # Bonding Pairs Bonding Capacity Li Be B C N O F Ne Apr 4 9:28 AM 9

10 Play video Bonding in a Molecular Compound ( Text p ) Covalent Bond is the force of attraction that exists between two nonmetallic atoms whose nuclei share an attraction \for the same pair of electrons. Feb 2 9:06 PM 10

11 Lewis Dot Diagrams for Molecular Compounds 1)Draw dot diagram for each element. 2)The atom with the most bonding electrons is placed in the centre with the other atoms bonded to it. 3)Count the number of bonding electrons for each atom and pair bonding electrons between atoms to form single, double or triple bonds. NO electrons are to be left unpaired. 4)Count to ensure each atom has an octet (except hydrogen & boron) Apr 4 9:31 AM 11

12 Molecular Elements two or more covalently bonded atoms of one type of element. Ex:Draw Lewis Dot Diagrams for H 2, Cl 2,O 2, N 2 single bond is when there is ONE electron pair shared between two atoms. double bond is when there are TWO electron pairs shared between two atoms. triple bond is when there are THREE electron pairs shared between two atoms. Feb 2 9:06 PM 12

13 Molecular Compounds contain two or more different kinds of nonmetallic atoms covalently bonded together. Structural Formulas are a simplified way to show bonding present in molecule. 1. a dash ( ) is used to represent a bonding pair of electrons. 2. lone pairs are omitted. Ex: Draw Lewis Dot Diagrams and Structural Diagrams for H 2 O, CO 2, CH 4, NH 3, CH 2 O, C 3 H 8, C 2 H 4, C 2 H 2, HCN, CH 3 OH Feb 2 9:06 PM 13

14 Play video Molecular Shapes All molecules have a definite 3 D shape. (MHR Text p ) Stereochemistry is a study of the shape of chemical species. Feb 2 9:11 PM 14

15 VSEPR Theory (Valence Shell Electron Pair Repulsion) Used to predict the molecular shape (geometry). Developed by Canadian chemist Ronald Gillespie. Molecular geometry can be determined from the Lewis Dot Diagram. Play video GjiDAaJGY&safety_mode=true&persist_safety_mod &safe=active Apr 4 9:32 AM 15

16 Rules for VSEPR Theory 1. Valence electron pairs, both bonding (shared) and lone pairs, arrange themselves around the central atom in the molecule so as to minimize repulsion. Therefore, the electrons are situated as far away from one another as possible. 2. Multiple bonds are treated as single bonds. 3. Actual shape will depend on how many pairs are bonding and how many are lone pairs. Feb 2 9:11 PM 16

17 This tutorial is a shockwave flash animation that I downloaded from Oct 19 1:42 PM 17

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26 Ionic compounds Draw Lewis dot diagrams for ions and Ionic compounds Feb 4 11:36 AM 26

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