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Chapter 5: Chemical Names and Formulas

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1 Chapter 5: Chemical Names and Formulas

2 Random Music to Lighten Your Day
Mike Stanfill, Private Hand - Flash Animation - The Elements, by Tom Lehrer

3 Elements to Memorize (Name and Symbol) – 32 Total
Hydrogen Lithium Sodium Potassium Magnesium Calcium Iron Chromium Manganese Cobalt Nitrogen Phosphorus Chlorine Bromine Neon Argon I HIGHLY recommend flash cards for these. Practice nightly. Nickel Copper Silver Gold Zinc Mercury Boron Carbon Aluminum Silicon Oxygen Sulfur Fluorine Iodine Helium Krypton

4 Common Polyatomic Ions (-1)
C2H3O2- HSO3- HSO4- HCO3- NO2- NO3- CN- OH- MnO4- ClO- ClO2- ClO3- ClO4- Acetate Hydrogen sulfite Hydrogen sulfate Hydrogen carbonate Nitrite Nitrate Cyanide Hydroxide Permanganate Hypochlorite Chlorite Chlorate Perchlorate

5 Common Polyatomic Ions (-2)
SO32- SO42- CO32- CrO42- SiO32- Oxalate Sulfite Sulfate Carbonate Chromate Silicate

6 Common Polyatomic Ions (Other)
PO43- Phosphate PO33- Phosphite NH4+ Ammonium

7 5.1 The Periodic Table Arranges elements according to similarities in their properties. Each column is known as a group. Groups 1-2, and are known as the representative elements. These exhibit the entire range of chemical properties. Made up of three basic groups Metals Metalloids Nonmetals

8 Metals On the left side of the periodic table.
High electrical conductivity and luster, ductile and malleable. With one exception, all are solid at room temperature. Groups 3 through 12 are transition metals, and groups at bottom are called inner transition metals or the rare earth metals.

9 Nonmetals Upper right of periodic table
Nonlusterous, generally poor conductors of electricity. Hydrogen is actually a nonmetal

10 Metalloids The elements that act as the “border” between metals and nonmetals. Has the properties of both metals and nonmetals.

11

12 Overall Periodic Table
We’ll get back to this topic later in the year. Pg. 108 has a good break-down of metals/non-metals and metalloids. On to naming!

13 5.2 – Atoms and Ions Normally, an atom is neutral. Why?
Sodium for example. Has 11 protons. How many electrons? 11 When forming a compound, Na will lose an electron. Now no longer has same # of protons as electrons. Now the sodium ion is positively charged.

14 Ions Ions are atoms or groups of atoms that have a positive or negative charge. To have a positive or negative charge, what must have happened? Must have gained or lost an electron Positive? Negative?

15 Metals tend to lose electrons during bonding.
An ion with a positive charge is called a cation. So a sodium cation would be represented symbolically as Na+ Na1+ also acceptable Magnesium (Mg) forms Mg2+. How many electrons did magnesium gain? Just kidding. How many did it lose?

16 Ion Naming For metals The name of the cation is exactly the same as the name of the element Sodium atoms (Na) form sodium cations (Na+) Potassium atoms (K) form potassium cations (K+) Even though the name is the same, they react differently. Sodium metal explodes when exposed to water Sodium cations are in salt-water, harmless

17 Nonmetals Atoms of nonmetallic elements tend to gain electrons.
They form anions, which are atoms or groups of atoms with a negative charge. Name of anion is NOT the same as the element. The name of the anion ends in –ide. Sulfur atom (S) forms sulfide anion (S2-) Bromine atom (B) forms bromide anion (B-)

18 5.3 Compounds From before, atoms of different elements may come together to form compounds. In many compounds, atoms are bound together to form a molecule. A molecule is an electrically neutral group of atoms that act as one unit. Compounds can be molecules

19 Compounds made from molecules are called molecular compounds.
Tends to have relatively low melting and boiling points. Many exist as gases at room temperature. Usually made from two or more nonmetallic elements. Not all compounds are made from molecules however.

20 Ions can join together to form ionic compounds
NaCl (table salt) is an example Ionic compounds are always formed from combining cations with anions. Although composed of ions, are ionic compounds are electrically neutral. Why? Almost always formed from metallic and nonmetallic elements.

21 Example of Ionic Compound

22 5.4 Chemical Formulas Over 10 million compounds have been identified. Some ionic, some molecular. No two have identical properties Composition can be represented by a chemical formula Shows the kind and numbers of atoms in the smallest representative unit of the substance

23 The molecular formula shows the number and kinds of atoms in a molecule or compound.
Water has two hydrogens bound to an oxygen Molecular formula of H2O Number of atoms of each element is given by the subscript written next to each element symbol Formula for ethane is C2H6. What is the composition of ethane?

24 Some elements exist naturally as molecules
Hydrogen, fluorine, oxygen, nitrogen, chlorine, bromine and iodine all are found in a molecular form in nature H2, F2, O2, N2, Cl2, Br2 and I2 These are called diatomic molecules Means they contain two of the same element

25 Formulas tell nothing about structure, only what’s it made from
Formulas can also be written for ionic compounds, though formula doesn’t represent a molecule Represents a formula unit The lowest whole-number ratio of ions in an ionic compound NaCl Shows lowest ratio is 1 Na+ to 1 Cl- Combine Mg2+ with Cl- MgCl2

26 Example of Ionic Compound

27 5.5 Laws of Definite and Multiple Proportions
Simply put, in any sample of a chemical compound the masses of the elements are always in the same proportions. Also, the number of atoms in a given compound are always in the same proportions. Skipping the math in this section.

28 5.6 Ionic Charges of the Elements
This section is super-important! To write formulas for ionic compounds, need to know what kind of ions atoms tend to form. Luckily, the periodic table will help with this! Here are the rules:

29 Ionic Rules Ionic Charges of Representative Elements 1A 2A 3A 4A 5A 6A
Li+ Na+ K+ Rb+ Cs+ Be2+ Mg2+ Ca2+ Sr2+ Ba2+ Al3+ Does not form ions N3- P3- O2- S2- Se2- F- Cl- Br- I- Nonmetals in 4A tend to be found in molecular compounds, not ionic compounds Elements in 8A do not tend to form compounds at all

30 Transition Metals and Ionic Charge
Unlike the cations of 1A, 2A and 3A, most transition metals have more than one common ionic charge. This is also characteristic of tin and lead (4A) For example, iron commonly forms Fe2+ and Fe3+. List of these common ions on pg. 120 (do not need to memorize) Basic rule (called the Stock system) Cu+ written as Copper(I) ion Sn2+ written as Tin(II) ion Mn3+ written as Manganese(III) ion

31 Exception for Transition Metals
Silver cations always have 1+ charge Cadmium and zinc cations always have 2+ charge.

32 5.7 Polyatomic Ions All of the ions we’ve discussed so far are formed from single atoms. Called monatomic ions Unlike those, there are other ions formed from groups of atoms so tightly bound together, they act as a single unit and carry a charge. Called polyatomic ions These are the compounds you need to memorize

33 Besides being composed of multiple atoms, act the same way as a normal ion
If an anion, will bond to a cation (or more than one) to balance out charges NO3- (nitrate anion) will readily bond with Na+ cation to form compound with formula NaNO3 Similarly, CO32- will bond with Na+ to form compound with formula Na2CO3 More on this later

34 5.8 Common and Systematic Names
In early days of chemistry, compounds often named after person who discovered them Or for the name to describe some property or source of the compound K2CO3 (Potassium carbonate) commonly called potash. Named this way because the compound was separated by boiling wood ashes in iron pots. Laughing gas (N2O), baking soda, quicksilver, all common names. Needed a common naming scheme. Going to learn this soon.

35 5.9 Writing Formulas for Binary Ionic Compounds
Binary Ionic Compounds are composed of TWO elements. Happens when two monatomic ions bond Remember, ionic compounds are electrically neutral So positive charge must equal negative charge Easy with K+ and Cl-. Charges exist in 1:1 ratio, so compound would be KCl

36 Even harder…remember, look at ratio of charges!
A little harder… Ca2+ and Br-. Charges exist in 2:1 ratio, so ions must combine in 1:2 ratio. Why is this? So formula should be CaBr2 Even harder…remember, look at ratio of charges! Iron (III) ion and oxide anion.

37 Ratio of charges is 3:2…not a simple thing to do
Iron (III) ion = Fe3+ Oxide anion = O2- Ratio of charges is 3:2…not a simple thing to do Need to find least common multiple of the charges What would it be? 6! To reach a charge of 6 for each, need 2 Fe3+ and 3 O2- Gives us formula of Fe2O3

38 Let’s try something a little different…
Sn3N4 What version of tin is this? To determine, need to figure out charge contributions N exists as N3- N contributes 12- charge So Sn must contribute 12+ charge Look at number of atoms in tin How many times does that number go into 12? 4 times! That is the positive charge on tin! So this ion is a Tin (IV) cation

39 5.10 Naming Binary Ionic Compounds
Very3 important section When dealing with NOT a transition metal: Is the name of the cation followed by the name of the non-metallic anion. MgCl2 Would be magnesium chloride K3N Would be potassium nitride

40 However, when dealing with the transition metals that can form more than one ion…things become a little more difficult In name, must include the Stock notation to identify cation formed by the transition metal CuO Copper oxide would be incorrect, because Stock notation not used First must determine which ion of copper is formed This is a Cu2+ ion. How do I know? So name would be Copper (II) oxide

41 Let’s try that again… SnO2 Again, Tin oxide would be incorrect
Need to determine charge on tin What would be charge on tin have to be? Sn4+ How do I know? Each O provides 2- charges, so oxygen provides a total of 4- charges Therefore, this is named tin (IV) oxide

42 5.11 Ternary Ionic Compounds
Ternary ionic compounds contain atoms of 3 different elements Hint: We’re going to use those polyatomic ions we talked about These are handled exactly the same way as a binary ionic compound, except that instead of 2 ions, we are using (usually) 1 ion and 1 polyatomic ion.

43 Example Sodium cation and nitrate anion. Na+ and NO3-
Charges exist in 1:1 ratio, so ions combine in 1:1 ratio So would be NaNO3

44 Another example, a little harder
Calcium cation and nitrate anion Ca2+ and NO3- Charges exist in 2:1 ratio, so we need 2 nitrates for every calcium Ca(NO3)2 What does the () mean? Means there are 2 of the NO3 polyatomic ions How many oxygens in this?

45 Naming Named just like binary ionic compounds
So previous example would be calcium nitrate

46 5.12 Naming Binary Molecular Compounds
This is for MOLECULAR COMPOUNDS, not ionic compounds, rules are slightly different How can we tell a molecular compound from an ionic compound? Molecular compound made from nonmetals. Ionic charges NOT used to assign formulas or names to these Two nonmetallic elements can also combine in more than one way Carbon and oxygen can form CO and CO2, also form two polyatomic ions, CO32- and C2O42-.

47 We use prefixes to name everything
For the previous carbon and oxygen compounds, the desire to call them carbon oxide can be strong. Resist this temptation Each of those compounds is very different We use prefixes to name everything

48 Table 5.5, page 131 Prefixes Used in Naming Binary Molecular Compounds
Number mono- 1 di- 2 tri- 3 tetra- 4 penta- 5 hexa- 6 hepta- 7 octa- 8 nona- 9 Deca- 10

49 How to Use Chart If I had CO molecule If CO2
Would use prefix mono- for the single oxygen Finally, ALL binary molecular compounds end in –ide. So this would be carbon monoxide. If first atom has only 1 of it, then we don’t use prefix on it. Which is why isn’t monocarbon monoxide. If CO2 Use di- prefix for oxygen Carbon dioxide

50 H2O 2 hydrogens so di-prefix 1 oxygen so mono-prefix Dihydrogen monoxide Also known as: Water Hehe…. Final rule: The vowel at the end of the prefix is dropped when the name of the element begins with a vowel. Which is why the above is monoxide, not monooxide.

51 Let’s try a few more I4O9 SF6 N5Cl10 Br7S8 Tetriodine nonoxide.
Sulfur hexafluoride N5Cl10 Pentanitrogen decachloride Br7S8 Heptabromine octasulfide

52 5.13 Naming Acids Don’t worry about this section for now, we’ll cover acids later

53 5.14 Summary for Naming Ionic compounds Always neutral
Positive charge = negative charge Metals always positive, nonmetals always negative When using a transition metal that forms more than one ion, must indicate which ion was formed by using Stock system. Should always end in –ide Polyatomic ions treated as a unit. They travel together

54 Molecular Compounds Must indicate how many of each element by prefix system If only 1 of the first element, does not need a prefix If element names starts with a vowel, and prefix ends with a vowel, drop the vowel on the prefix

55 Homework 22-26, 28-30


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