Bonding and Chemical Reactions

Transcription

1 Bonding and Chemical Reactions

2 Introduction Assignment- Chapter 5 Group 1: Describe the difference between compounds and mixtures. Group 2: Describe how the chemical structure of a compound affects its properties-four ways..explain. Group 3:Explain why atoms sometimes join to form bonds. Group 4: What is an ionic bond, why it forms, and characteristics. Group 5: What is a covalent bond, why it forms, and characteristics.

3 Compounds Pure substance made of two or more elements that are chemically joined. They do not look or act like the elements that formed them.

4 Chemical Bonds A chemical bond is the force that holds particles together. Octet Rule atoms bond in order to get 8 valence electrons Atoms either give up, take, or share electrons to get a full outer energy level. A chemical bond formed by the transfer of electrons is an ionic bond. A chemical bond formed by the sharing of electrons is a covalent bond.

5 Electron Dot Diagrams/Lewis Structures Consist of symbols with dots around them indicating valence electrons X Examples: Na Cl O Mg N C

6 Ionic Bonds Ionic bonds always result when a metal and nonmetal are together Formed when electrons are transferred from one atom to another. One atom gains electrons while another atom loses electrons. They do this to be like the noble gases. Oxidation numbers give us the loss or gain information.

7 Ionic Bonds Ionic bonds are a result of positive ions (cations) bonding with negative ions (anions) Example Mg Br

8 Bonding Comparison

9 Ionic Bonds Ions can exist as single ions or as polyatomic ions (a group of atoms with an overall charge) Examples: ammonium (NH 4 +1 ) carbonate (CO 3-2 ) nitrate (NO 3-1 ) sulfate (SO 4-2 ) chlorate (ClO 3-1 )

10 Characteristics of ionic compounds Form crystal lattice structures High melting points and high boiling points WHY? Very brittle As a solid, do not conduct electricity unless melted or dissolved in water. ions can then flow and carry a charge DEMO

11 Covalent Compounds Formed by bond made by the sharing of electrons. Atoms share to get a full outer energy level. Covalent compounds can have multiple bonds: single bonds: 1 pair of electrons shared example: H 2, Cl 2 double bond: 2 pairs of electrons shared example: O 2 triple bond: 3 pairs of electrons shared example: N 2

12 Covalent Compounds Atoms can also share with other atoms Examples: HCl CH 4 CO 2 H H-C-H H O=C=O

13 Bonding Comparison

14 Naming Simple Compounds Rules for naming More than 2 elements Metal and a polyatomic group K 2 (CO 3 ) Write name of metal** and name of group Only 2 elements Metal-nonmetal (ionic) KBr Write name of metal** and name of nonmetal(change the ending to ide) Nonmetal-nonmetal (covalent) SCl 4 Write the name of the element furthest to the left or top of table 1 st, and then the other element with the ending changed to ide. Use prefixes to state the number of atoms in the compound. No prefix on the first element if there is only one. **Use Roman Numerals for variable valence metals. CuCl 2

15 Bond Energy Energy is needed to break the bonds holding compounds together. Compounds with more bonds, take more energy. Compounds with different types of elements bonded together require more energy than ones with only one type of bond. Examples: NaCl CaCO 3

16 Chemical Equations and Reactions Chemical Reaction: Process by which a chemical change happens. Law of Conservation of Matter applies can t create or destroy, but can rearrange Chemical equations show what occurs in a chemical reaction

17 Chemical Equations and Reactions Left side called reactants Right side called products Reactants=Substances react with each other Products=New substances formed from a reaction Equations must be balanced with equal numbers of elements on both sides of the equation using coefficients

18 Types of Reactions Synthesis/Composition General Formula: A + B AB Two simple substances combine to form a more complex one. Final equation must be balanced Example: Na + Cl 2 NaCl balanced??? 2Na + Cl 2 2NaCl

19 Types of Reactions Decomposition General Formula: AB A + B One complex substance breaks into two simple ones. Final equation must be balanced Example: NaCl Na + Cl 2

20 Types of Reactions Single Replacement General Formula: A + BC B + AC Element + Cpd New Cpd + New Element Single element switches with a similar metal or nonmetal element. Final equation must be balanced Example: NaCl + Mg MgCl 2 + Na balanced? 2NaCl + Mg MgCl 2 + 2Na

21 Types of Reactions Double Replacement General Formula: AB + CD AD + CB Cpd1 +Cpd2 Cpd3 + Cpd4 Two different elements in two different compounds switch places. Final equation must be balanced Example: MgBr 2 + AlCl 3 AlBr 3 + MgCl 2 3MgBr 2 + 2AlCl 3 2AlBr 3 + 3MgCl 2