Unit 4 – Compounds and Bonding

What Do You Remember? 1) Define Compound Substance formed by 2 or more elements in which proportions are always the same 2) Give two example of a compound H20, NaCl, CO2 3) Define Element Substance with atoms that are all alike 4) Give two example of an element Any from the periodic table

6) Give an example of a mixture 5) Define Mixture A material made up of 2 or more substances that can be easily separated by physical means 6) Give an example of a mixture Soda, salad dressing, soup mixes, granite, cheese 7) What are 2 physical properties of iron? Malleable, luster, ductile, good conductor of heat and electricity

8) What are 2 physical properties of sulfur? - solid at room temp, brittle, no luster, not malleable 9) How is iron sulfide different from the 2 elements that make it up? - when you combine iron and sulfur it smokes 10) When iron sulfide is formed, is it a physical or a chemical change. - chemical change (making a new substance)

a) Can be separated by physical means? 11) If you mixed the iron and sulfur together, would that be a chemical or physical change? Physical – can separate by using a magnet 12) Mixture or Compound? a) Can be separated by physical means? mixture b) No definite chemical composition c) Maintains same properties as original compounds

13) Draw a Bohr Diagram of Nitrogen

14) Mixture, Compound, or Element a) Salt Water - mixture b) Salt - compound c) Phosphorus - element d) Hydrochloric Acid e) Einsteinium f) Sugar g) Hydrogen Peroxide h) Carbon Monoxide

Stability in Bonding Sodium (Na) and Chlorine (Cl) together can make up sodium chloride (NaCl) Compounds such as sodium chloride have properties that aren’t like any of those of the individual elements A chemical formula - tells what elements a compound contains and the exact number of atoms of each element NaCl – 1 molecule of sodium and 1 molecule of Chlorine

Some Familiar Compounds Water – H2O Salt - NaCl Sucrose – C12H22O11 Glucose – C6H12O6 Hydrochloric Acid – Stomach Acid – HCl Sulfuric Acid – Battery Acid – H2SO4 Dinitrogen oxide – Laughing Gas – N2O

Most of the elements can combine with other elements The 6 noble gases in Group 18 rarely form compounds because the atoms are unusually stable

Electron Dot Diagrams Only show the electrons in the outer energy level of an atom – Valence Electrons Don’t have to show energy levels

VALENCE ELECTRONS Elements in group 1 have 1 outer electron Elements in group 2 have 2 outer electrons Skip transitional metals (the energy levels are similar to groups 1 and 2) Elements in group 13 have 3 outer electrons Elements in group 14 have 4 outer electrons, and so on

Steps to Drawing Dot Diagrams: Write chemical symbol Find how many valence electrons are in element Draw dots around symbol

Let’s try drawing some of these… K Mg Al Na Cl

Atoms with partially stable outer energy levels can lose, gain, or share electrons to obtain a stable outer energy level. Note that there is 1 electron in the outer level of Na and 7 in Cl. When they combine, sodium loses one electron and chlorine gains one Hydrogen and oxygen share electrons to become more stable in the compound water

A chemical bond is the force that holds atoms together in a compound.

Ionic and Covalent Bonding Why do most elements form compounds? Become more stable – atomic stability More resistance to change Elements are most stable when they have 8 electrons on their outermost energy level MAGIC # is 8! Atoms are happy  when their outer energy levels are full!

Valence Electrons – the electrons that are involved in forming chemical bonds (outer energy level) Correspond to the groups; elements in the same group have the same number of valence electrons Except He (only has 2 electrons) and transitional metals vary

Examples:

How many valence electrons do the following atoms have? Na – 1 Ar – 8 F – 7 In general, an atom will form a chemical bond with another atom so that both atoms will have 8 electrons in their outer energy level. (Exception: Noble Gases)

Two main types of chemical bonds: Ionic Covalent

Ionic Bonds (IT – Ionic Transfers electrons ) Force of attraction between opposite charges of ions Transfer electrons Non-metal and metal Ex. NaCl High boiling point, high melting point, conducts electricity Crystalline solids

Covalent Bonds (CS – Covalent Shares electrons) Attraction that forms between atoms when they share electrons Non-metal and non-metal Ex. H2O Low boiling point, low melting point, doesn’t conduct electricity Molecules http://www.youtube.com/watch?v=QqjcCvzWwww

Identify the element, number of valence electrons and would the element develop a covalent bond, ionic bond, both or neither.

Organic Compounds Organic compounds – most of the compounds that contain the element CARBON Organic compounds make up all living things or things that have lived

90% of all compounds are organic!

Compounds such as carbon dioxide and the carbonates are considered inorganic. Inorganic compounds are mostly compounds not containing carbon

Why can carbon form so many compounds? 4 electrons in outer shell 4 covalent bonds Can bond with many elements (especially hydrogen and oxygen) Can link with other carbon atoms in different arrangements C

To determine molecular structure of organic compounds use the following formula: CnH2n + 2

Examples of organic molecules Methane gas (CH4) H H C H H

Propane gas molecule (C3H8)

Hydrocarbons – a compound made up of only carbon and hydrogen atoms Hydrocarbons are currently the main source of the world’s electrical energy and heat sources (such as home heating) because of the energy produced when burnt Ex. Methane, propane, butane, octane

Writing Formulas: Criss-Cross Method 1) Write down chemical symbols 2) List oxidation numbers in the upper right hand corner of each symbol Oxidation number – tells you how many electrons an atom has gained, lost, or shared to become stable To find the oxidation number take the 8 – valence electrons. (for groups 13-18)

Oxidation Number of Groups: Group 18 = 0 (remember…they don’t combine anyway)

4) Criss-cross the oxidation numbers to the new location 3) Next to the number in the right hand corner, write down + for metals, and – for non-metals. The element with the + oxidation number is written first The element with the – oxidation number is written second 4) Criss-cross the oxidation numbers to the new location 5) Drop the + or – and rewrite the formula.

Example:

Examples: Ag + S → Li + F → Ba + Cl → Ca2 + B-5 → Fe+2 + Ar →

Chemical Reactions What is a chemical reaction? When substances go through a chemical change and form new substances with different properties. What are some examples of chemical reactions? Rusting of iron Souring of milk Burning of paper Cooking an egg

2 Parts of a chemical reaction: Reactants - substances that enter into a reaction Na + Cl  NaCl Products - substances produced by a reaction Example: What are the reactants and products in the rusting of iron? Reactants Iron, water and oxygen Products Rust (Iron Oxide)

Rusting is a chemical reaction Rusting is a chemical reaction. The reactants are iron and oxygen and the product is iron oxide (rust). For rusting to occur, the iron atoms must lose some of their electrons (negative particles that travel around the nucleus of an atom), and the oxygen must gain them. Water is needed for rusting to occur because the electrons that the iron loses travel through the water.

How does a chemical reaction occur? An atom will try to get 8 valence electrons by breaking existing bonds and rearranged to form new bonds. A convenient way to express a chemical reaction is by writing a chemical equation: 4Fe + 3O2  2Fe2O3 coefficient reactants “yields” products

http://www.youtube.com/watch?v=dExpJAECSL8 Law of Conservation of Mass Matter cannot be created or destroyed during a chemical reaction (it can only be rearranged) The total mass of the reactants EQUALS the total mass of the products. Example: 2H2 + O2  2H2O If the total of 5 grams of Hydrogen and Oxygen gases were combined, then ______ of water would be obtained. Answer: 5 grams http://www.youtube.com/watch?v=x9iZq3ZxbO8 http://www.youtube.com/watch?v=dExpJAECSL8

Balanced Chemical Equations A chemical equation must show that atoms are NOT created or destroyed. Must have the same number of atoms on both sides Cannot add subscripts – use coefficients to balance equations

Is this equation balanced? H2 + O2 → H2O No there are 2 oxygen in reactants and only 1 in products How can we balance it? 2H2 + O2 → 2H2O

Balance the following equations by using coefficients (“numbers in front of substances”): a. Ag + S  Ag2S 2Ag + S  Ag2S b. Al + HCl  H2 + AlCl3 2Al + 6HCl  3H2 + 2AlCl3 c. KI  K + I2 2KI  2K + I2 d. K + O2  K2O 4K + O2  2K2O

Agenda for 12/17/15 BELLRINGER: BALANCE THIS PROBLEM Zn + HCl  ZnCl2 + H2 Go over homework Types and Signs of Chemicals Reactions Types of Chemical Reactions worksheet HW – Chemical Reactions worksheet #2 TEST TUESDAY

More Balancing Equations 2Na + Cl2 → 2NaCl 2H2 + O2 → 2H2O CH4 + 2O2 → CO2 + 2H2O 2K + Cl2 → 2KCl N2 + O2 → 2NO

More Balancing Equations 6) Zn + 2HCl → ZnCl2 + H2 7) N2 + 3H2 → 2NH3 8) Na2SO4 + CaCl2 → CaSO4 + 2NaCl 9) 2C2H6 + 7O2 → 4CO2 + 6H2O 10) 3Mg + N2 → Mg3N2

Signs that a chemical reaction has taken place: 1) Change in color

2) Formation of precipitate (formation of a solid when there was none)

3) Release of gas

4) Light is released

5) Energy changes occur a) Exothermic reaction – gives off energy; gets warmer Example: burning of wood, explosion of dynamite, Gummy Bear demo, Genie in a Bottle demo b) Endothermic reaction – absorbs energy; gets cooler Example: dissolving Epsom salts, reaction of Ba(OH)2 and NH4Cl

Types of Chemical Reactions: 1) Synthesis – 2 or more substances combine to form a single, complex product Examples: 2Mg + O2 → 2 MgO 4Fe + 3O2 → 2Fe2O3 (rust)

2) Decomposition – a complex substance is broken down into two or more simpler substances (opposite of synthesis) Example: Splitting water by electricity 2H2O → 2H2 + O2

3) Single Replacement – a free element replaces an element in a compound Example: Cu + 2AgNO3 → 2Ag + Cu(NO3)2

4) Double replacement – when two ions switch places in a reaction Example: Pb(NO3)2 + 2KI → PbI2 + 2KNO3