Chapter 6 Section 1 Compounds and Molecules Structure of Matter Chapter 6 Section 1 Compounds and Molecules

Let’s Review! An element is made up of entirely the same atom It is something that can not be broken down any further. Compounds are pure substances composed of the same ions and/or molecules. Compounds can be broken down into other substances.

Chemical Bonding Joining atoms to form new substances (molecules) This is a chemical change, the new substances will have different properties than the original elements. Chemical bonding involves valence electrons

Chemical Bonding Atoms are most stable (happy) with a full valence shell. A full valence is normally 8 e- (for H, He, Li and Be it is 2) Bonding is when atoms share or transfer electrons in order to get to a full valence shell.

Chemical Structure Chemical Structure: how the atoms are bonded together to make the compound Water’s chemical formula, H2O, tells us WHAT is in it, but it doesn’t tell us HOW it is put together or how it acts.

Bond Length and Angle Bond Length: the distance between nuclei of two bonded atoms Bond Angle: the angle formed by two bonds to the same atom, tells which way these atoms point.

Chemical Compounds Section 2

Let’s Recall… Why do atoms bond? To have a stable electron configuration

Types of Bonds Three kinds of chemical bonds Ionic, Covalent, Metallic The way a compound bonds determines many of its properties

Ionic Bonds Ionic Bonding: a transfer of electrons (something gains, something loses) Form from the attraction of oppositely charged ions Ionic bonds occur between metals (cations) and nonmetals (anions)

Ionic Compounds Ionic bonds are held together by electromagnetic force (opposites attract) Compounds with ionic bonds are ionic compounds Form networks, not molecules For example Na+ is attracted to Cl- when large amounts get together, they stack in a crystal arrangement

Properties of Ionic Compounds Examples of ionic compounds Salts, baking soda, and rust Brittle – tend to shatter when hit High Melting points – most don’t melt until they are very hot Solubility – many tend to dissolve in water.

Dissolving Ions If you dissolve ions in water, they will break into parts, some with a positive charge, some with a negative charge This difference in charge is why IONIC COMPOUNDS conduct electricity Electrolyte: anything dissolved in water that increases conductivity

Covalent Bonds Covalent Bonding: a sharing of electrons Usually between nonmetals

Covalent Bonds Structural formula for a covalent bond is shown as a single line More than one pair of electrons can be shared, and there will be an additional line for each pair shared

Covalent Bonds Covalent bonds can also be shown with a Lewis Dot diagram The valence electrons of the atom are drawn around the atom symbol Bonded molecules are drawn with the dots being shared

Covalent Compound Covalent Compounds are made of molecules. Molecules are atoms that share electrons in a bond. Covalent compounds can be solids, liquids or gases

Properties of Covalent Compounds Examples Glass, rubbing alcohol, nitroglycerin, and natural gas Low melting points – several exist as gases or liquids at room temperature. Most covalent compounds do not dissolve in water or produce positive and negative particles if they dissolve. Therefore most covalent compounds do not conduct electricity by themselves.

Metallic Bonding Bonds between metals Sharing and transfer of electrons Metallic bonds only occur with the same metal, not with others Ca can bond with other Ca atoms, but not Ba

Metallic Bond In metallic bonds, the valence electrons become community property, traveling anywhere they want to throughout the metal’s packed structure. The outermost energy levels overlap, and the electrons are free to move from atom to atom This “Sea of Electrons” is why metals are such good conductors of electricity and heat.

Compound Names and Formulas Section 3

Remember: Valence electrons are the ones that want to react Metals have fewer valence electrons, so they will give up 1, 2, or 3 electrons (cations) Nonmetals have more valence electrons, they will gain 1, 2, or 3 valence electrons (anions)

Naming Ionic Compounds Ionic bonds are between metals and nonmetals The name of an ionic compound consists of the names of the ions in the compound The metal is always named FIRST, and the nonmetal LAST

Naming Ionic Compounds The cation (metal) name will remain the same The anion (nonmetal) name will change drop the ending and add “-ide” For example – F- fluoride Cl-, O2-, C4- chloride, oxide and carbide Ions of chlorine and sodium give you sodium chloride (metal) (nonmetal)

Determining Formula of Ions Ions have different charges Ionic compounds want to have an overall charge of 0 (this makes them neutral and stable) Total positive charge = total negative charge For example: Na+ and O2- 2 sodium for every one oxygen Na2O

Determining Formula of Ions Example: BORON OXIDE Write the symbols of both elements (cation 1st, anion 2nd) Write the valence of each as a superscript Drop the positive and negative signs Crisscross the superscripts so they become subscripts Reduce when possible (not possible here) B O B3+ O2- B3 O2 B3 O2 B2O3

Let’s Practice! Al3+ and O2- Al2O3 Aluminum oxide K+ and Cl- KCl Potassium chloride Sr2+O2- Sr2O2  SrO Strontium Oxide The subscripts don’t effect the name if there is only one possibility

Determining Formula of Ions Some metals form different cations with different charges These are all metals that aren’t in group 1, 2 or aluminum – the transition metals! The cation charge follows the symbol as a roman numeral For example iron can form Fe2+ or Fe3+ These are said as iron (II) and iron (III) Cu+ and Cu2+ Copper (I) and Copper (II)

Covalent Naming Covalent bonds involve shared electrons, so there are no charges You still drop the ending of the second atom and replace it with the suffix “-ide”. Ionic names ignored the subscript numbers. Covalent does not Prefixes are used in the name, they tell you how many atoms of the element are in the compound You cannot reduce these formulas!

Prefixes prefix meaning *mono- 1 hexa- 6 di- 2 hepta- 7 tri- 3 octa- 8 tetra- 4 nona- 9 penta- 5 deca- 10 *“mono-”, it just keeps its original name!

Examples CO carbon monoxide CO2 carbon dioxide NI3 nitrogen triiodide P4O6 tetraphosphorus hexoxide

Continuing I4O9 tetriodine nonoxide S2F10 disulfur decafluoride IF7 Iodine heptafluoride Si2Cl6 disilicon hexachloride