The Structure of Matter Section 6.1: Compounds and Molecules What holds a compound together? How can the structure of chemical compounds be shown? What determines the properties of a compounds? Types of Chemical Bonds Video 1
Compounds Result from way atoms or ions are joined Similarities & differences of various compounds When elements combine, the resulting compound has properties very different from those of elements that make it Always have same chemical formula 2
What are bonds? A Chemical Bond is an attractive force that holds atoms or ions together. Atoms bond when their valence electrons interact. This way, the outermost energy level of the atom is full. (Octet Rule) Wannabe Noble Gases Bonds are Flexible Bonds are NOT like toothpicks, they ARE like springs There are many models of molecules, but the atoms are not stuck in place. Atoms move back and forth. 3
Chemical Structure Chemical Structure is the way the compounds atoms are bonded to make the compound. Bond length is the distance between the nuclei of two atoms. You can see this in the ball-and-stick model. Compounds with three or more atoms have bond angles. Models Ball-and-stick Ball represents atoms, stick represents bonds Space-filling Shows that atoms the right size and in the right place. Structural Uses chemical symbols to represent atoms. H O H H H C O H H 4
How does Structure Affect Properties? The chemical structure of a compound determines its properties. Network Structures: Atom bonds Compounds with network structures are strong. Ex) SiO 2 / quartz Stone mountain Ga How does Structure Affect Properties? Networks with bonded ions: oppositely charged ions High melting and boiling points Example: NaCl / table salt 5
How does Structure Affect Properties? Compounds made of molecules Sugar, CO 2, N 2, O 2 Weak attractions between each molecule, despite the strong attraction between the atoms that make up each molecule. How does Structure Affect Properties? Different molecules have different strengths of attraction. The stronger the attraction between molecules, the higher the boiling and melting points. When Hydrogen is attracted to an atom of another molecule, this is called a hydrogen bond. 6
Section 6.2: Ionic and covalent bonding Why do atoms form bonds? How do ionic bonds form? What do atoms joined by covalent bonds share? What gives metals their distinctive properties? How are polyatomic ions similar to other ions/ Ted talk video: Chemical Bonds Why Do Chemical Bonds Form? Atoms bond so each will end up with a stable electron configuration Full outermost s and p orbitals To become more stable 7
Electron Dot diagram A way of keeping track of valence electrons. How to write them -RLTB Write the symbol. Put one dot for each valence electron Don t pair up until they have to X Electron Dot diagram l l Nitrogen has 5 valence electrons. First we write the symbol. lthen add 1 electron at a time to each side. N luntil they are forced to pair up. 8
Write the electron dot diagram for the following elements. Na Mg C F Ne He O Electron Configuration Cations Metals lose electrons to fill their outer levels They make positive ions. Anions Nonmetals gain electrons to fill their outer levels They make negative ions. Ca Ca 2+ P P 3-9
What are 3 ways that atoms can form bonds? 1. Ionic bonds Transferring electrons 2. Covalent bonds Sharing electrons 3. Metallic bonds Many free electrons Valence electrons from one atom are transferred to another atom. They become charged ions Ionic Bonds Positive and negative charged ions are attracted to each other. 10
Example Sodium (Na) (Explosive metal)! Chlorine (Cl) (toxic gas!) Ionic Bonds Very strong bonds that form between ions with opposite charges. Cations and anions 11
Ionic Bonds In the form of networks, not molecules. Forms crystal lattice. Ionic Compound not molecules Ionic Bonds When you melt or dissolve ionic compounds in water, the ions are free to move around. This allows them to conduct electricity! Copyright 2010 Ryan P. Murphy 12
Ionic Compounds Sodium Chloride: NaCl, or 1 Na+ for every 1 Cl-ion. Calcium Fluoride: CaF 2, or 1 Ca 2 + for every 2 F-ions. Ionic Bonds Na Cl +1 1 13
Ionic Bonds Na Cl +1 1 Ionic Bonds Mg O +2 2 14
Ionic Bonds Mg +2 O 2 Ionic Bonds Cl 1 +2 1 Mg Cl 15
Ionic Bonds Cl 1 +2 Mg Cl 1 Chemical Formula = MgCl 2 Ionic Bonds Al O Al O O 16
Ionic Bonds +3 Al O 2 Al +3 2 O O 2 Ionic Bonds +3 Al O 2 +3 Al O 2 O 2 Chemical Formula = Al 2 O 3 17
Oxidation Numbers Remember that the charge of an ion can be determined by its place on the Periodic Table. 1+ 0 2+ 3+ 4 + 3-2- 1- Variable oxidation numbers This will be given to you. Look for the Roman Numeral! 4 - or For each elements on your notes, predict the charge of its most common ion using the periodic table. -3 +1-2 0 +2 +1 +2-1 -3 +2-2 +1-1 +1-1 0-1 0 18
Transition metals are less predictable. Form positive ions because they are metals. The charges are important in determining the formula of an ionic compound. What are the charges of the transition metals below: +2 +3 +2 +1 +4 +2 +2 +4 Iron (II) Copper (II) Tin (IV) Lead (II) iron (III) oxide Fe +3 O -2 Iron (III) Copper (I) Tin (II) Lead (IV) Writing Binary Ionic Formulas Steps for writing chemical formulas using oxidation numbers 1. Write the chemical symbols for the cation (first) and anion (second). Metal 1 st Nonmetal 2 nd 2. Write the oxidation number on top of the Chemical Symbols for the cation and anion. The 1 is understood. 3. Kris cross the oxidation numbers writing each number as a subscript for the other atom or polyatomic ion. 4.Reduce Subscripts if they can be reduced Mg +2 I MgI 2 magnesium iodide Ca 2 0 2 = Ca 2/2 O 2/2 = CaO Pb 2 O 4 = Pb 2/2 O 4/2 = PbO 2-19
Rules for Naming Binary Ions 1. The names of metals do not change. 2. Changing the name of nonmetals: Root of element name + -ide = name of ion Examples: The name of chlorine s ion: chlor- + -ide = chloride The name of nitrogen s ion: nitr- + -ide = nitride Rules for Naming Ions Examples of naming ions: The name of calcium s ion: calcium (The names of metals don t change!) The name of oxygen s ion: ox- + -ide = oxide The name of aluminum s ion: aluminum (The names of metals don t change!) 20
Rules for Naming Ions Write the name of each of the ions. sulfide nitride potassium oxide lithium bromide chloride hydrogen (+), hydride (-) Name the following Ions 1. NaF sodium fluoride 3. SrCl 2 strontium chloride 5. CaO calcium oxide 2. MgO magnesium oxide 4. Li 2 S lithium sulfide 6. KI potassium iodide 21
Name the Ions (transitional Metals) 1. CuCl Copper (I) chloride 3. ZnS Zinc (II) sulfide 5. NiO Nickel (II) oxide 2. PdO 2 Palladium (IV) oxide 4. Ni 2 O 3 Nickel (III) oxide 6. MnBr 4 Manganese (IV) bromide Write the formula (transitional Metals) 1.Copper (I) chloride CuCl 3. Chromium (I) Sulfide CrS 2. Lead (IV) Oxide PbO 2 4. Nickel (II) Oxide NiO 5. Silver (II) Fluoride 6. Manganese (II) Nitride AgF 2 Mn 3 N 2 22
Rules for Naming Ions Polyatomic Ions Ions that form after elements have shared electrons. Each polyatomic ion already has a name. Ends in ateor ite. Write the polyatomic ion name. sulfate permanganate hydroxide carbonate sulfite nitrate Polyatomic Ions vs Ions from the PT Be very careful that you do not mix up the names of ions. Decide which name goes with each ion. nitrate nitride N -3 NO 3 - S -2 sulfide SO -2 sulfite 3 P -3 phosphate PO -3 phosphide 4 23
Rules for Naming Polyatomic Ions This is just as easy to do with polyatomic ions. You just need to use the name of the polyatomic ion. Step 1: Write the symbol of the metal ion. Step 2: Write the formula of the polyatomic ion. Step 3: Determine the charges using the periodic table and the table of polyatomic ions. Step 4: Determine the formula from the ions. strontium nitrate ( ) +2 - Sr NO 3 Sr(NO 3 ) 2 The atoms in parentheses reminds us they are a single ion. Figure out the polyatomic ion formula. 1. Potassium hydroxide 2. Sodium carbonate KOH Na 2 CO 3 3. Hydrogen carbonate 4. Calcium chlorate H 2 CO 3 Ca(ClO 3 ) 2 Figure out the polyatomic ion name. 1. NH 4 F ammonium fluoride 3. Mg(NO 3 ) 2 magnesium nitrate 2. CaSO 4 calcium sulfate 4. NaOH sodium hydroxide 24
Practicing naming ionic compounds calcium chloride potassium sulfide potassium permanganate barium oxide ammonium chloride cesium chloride magnesium sulfate sodium bromide aluminum phosphide Zinc (II) Chloride ZnCl 2 CuO Copper (II) Oxide Pb3N Lead (I) Nitride Practicing Writing Ionic Compound Formulas KI SnCl 4 BaSO 44 NaCl SrS CuCO 3 AlBr 3 Li 3 N 25
Covalent Bonds Formed by nonmetals and Hydrogen Nonmetals hold onto their valence electrons, but want a full outer shell A bond formed when two atoms share electrons. Atoms may share more than one pair of electrons. Different from an ionic bond because they actually form molecules. Shared electrons A double bond is when atoms share two pair (4) of electrons. A triple bond is when atoms share three pair (6) of electrons. Covalent Bonds Another way of indicating bonds Often use a line to indicate a bond Called a structural formula Each line is 2 valence electrons H O H =H O H 26
Covalent Bonds Atoms do not always share electrons equally. Nonpolar Covalent Bond- electrons are shared equally. Polar Covalent Bond- Unequal sharing of electrons Covalent Bonds F F Shared pair of electrons 27
Covalent Bonds H O H Covalent Bonds H O H How many valence electrons does oxygen each hydrogen now have? now have? 28
Covalent Bonds Okay, now try this one... C O O Covalent Bonds There are 7 elements that exist in nature as diatomic molecules. What elements exist as diatomic molecules? H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 29
Covalent Bonds There are millions of covalent compounds. You will be learning about the easiest type of covalent compound to name: Binary Covalent Compounds What does binary mean? Binary means 2. Binary covalent compounds are between 2 different nonmetals. Covalent Bonds Nonmetals can share electrons in many different ways. Two nonmetals can create multiple compounds together. carbon and oxygen CO CO 2 nitrogen and oxygen N 2 O 4 N 2 O 3 phosphorous and chlorine PCl 3 PCl 5 30
Covalent Bonds Important Facts: Hydrogen only has 1 proton and 1 electron Behaves differently than any other element on the PT H + H - Hydrogen can donate its 1 electron. Hydrogen can gain 1 electron. Hydrogen can share electrons. This means that hydrogen can act as either a metal or a nonmetal! H 2 Covalent Bonds To show the correct ratio of elements, we use prefixes. Remove the -oor - a from a prefix before adding it element. Leave -i alone. 31
Covalent Bonds How would you write each of the prefixes in front of oxide? mono- monoxide tri- trioxide penta- pentoxide hepta- heptoxide nona- nonoxide di- dioxide tetra- tetroxide hexa- hexoxide octa- octoxide deca- decoxide Naming Binary Covalent Bonds Step 1: Write the name of the first nonmetal. Step 2: Write the name of the second nonmetal changing its ending to -ide. Step 3: Add prefixes to specify how many of each element are present. dinitrogen tetroxide N 2 O 4 32
Covalent Bonds Rules for Using Prefixes Rule 1: Prefixes are only for BINARY COVALENT compounds. Rule 2: The prefix mono-is never used on the first element of a binary covalent compound. It is assumed that there is only 1. Example: CO 2 is carbon dioxide, and not monocarbon dioxide. Rule 3: Remove the -oor -afrom a prefix before adding it to oxide. Example: CO is carbon monoxide, and not carbon monooxide. Name the binary covalent compounds carbon dioxide carbon disulfide phosphorous tribromide phosphorous pentabromide diphosphorous pentasulfide dinitrogen monosulfide silicon disulfide nitrogen tribromide dinitrogen tetrachloride 33
Writing Covalent Bonds formulas Because of the prefixes, it is very easy to go from the name of a binary covalent compound to its formula. Step 1: Write the symbol of the first nonmetal and the subscript that matches the prefix. Step 2: Write the symbol of the second nonmetal and the subscript that matches the prefix. dinitrogen tetrafluoride N 2 F 4 What is it? 34
Covalent Bonds Write the formulas of the binary covalent compounds CCl 4PCl5 N 2 O CS BH 3 S 2 Br 6 SiS 2 PI3 NCl 3 IF 7 N 2 O 4 PCl 3 CO IClS4N4 NO 2 H 2 O ClF 5 Metallic Bonds The bonding between atoms within metals. The sharing of many free electrons. Sea of electrons Metals are flexible and conduct electric current well Their atoms and electrons can move freely throughout a metal s packed structure. 35
Empirical vs Molecular formulas The empirical formula tells us the simplest formula, or the smallest whole-number ratio of atoms in a compound. Different compounds can have the same empirical formula (ratio of atoms). The molecular formula tells you exactly how many atoms are in one molecule of a compound. All compounds have different molecular formulas. Compound Emp. Form. Mol. Form. Formaldehyde CH 2 O CH 2 O Acetic acid CH 2 O C 2 H 4 O 2 (x2) Glucose CH 2 O C 6 H 12 O 6 (x6) 36
Acids and Bases Svante Arrhenius was a scientist who defined acids and bases. This is the simplest definition of an acid and a base. He defined an acidas any substance which donates a hydrogen ion(h + ). He defined a baseas any substance which donates a hydroxide ion (OH - ). Review What elements do ionic compounds contain? Ionic compounds contain a metaland a nonmetal. What elements do covalent compounds contain? Covalent compounds contain only nonmetals. 37
Review Decide whether the compounds are ionic or covalent. I C I I C C I I I C C I Review Write the formulas of the compounds. HCl BaF 2 SnS N 2 O CS 2 S 2 Cl 6 Na 3 PO 4 PtCl 2 38
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