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Chapter 5 Chemical Names and Formulas
I.
Introduction –
- Elements are the building blocks of all living and nonliving things
- Most of the 118 elements are unstable in nature so they combine to form compounds to become stable
- These 118 elements can combine differently and in different ratios to form an almost unlimited number of
compounds
- These compounds are all identified by a unique chemical formula
II.
The Periodic table
- The periodic table was developed through the efforts of Newland Mendeleev and later refined by Moseley
- The periodic table list elements from left to right according to their atomic numbers this causes the elements
to be arranged according to their similarities and differences
- Each horizontal row in the period table is called a period (1-7)
- The closer elements are to each other in the period the more properties they have in common
- Each vertical column of elements in the periodic table is known as a group
- There are 18 groups of elements they are designated by a number-letter combination
- The Group A elements are known as the representative elements
- The representative elements include the entire range of chemical properties (metals, metalloids, and
nonmetals)
- Elements on the left of the periodic table are the metals
- Metals properties: conductors, high luster, ductile, malleable, free electrons, most solid at room temperature
(mercury)
- 80% of all elements are metals
- The metals include the transition metals, which are group B elements, and the inner transition metals, which
are called the rare earths
- The nonmetals are found in the upper right hand corner of the periodic table
- Nonmetal properties: insulators, nonlustrous or dull, brittle, no free electrons, found as solids, liquids, and
gases
- Elements in group 18, 0, or 8A are called the noble gases because they do not react with other elements
- Stair-step line divides the metals and the nonmetals
- Most elements on each side of the stair-step line are metalloids
- Metalloids have properties of both metals and nonmetals
Concept practice
1. Identify the following elements as metals, metalloids, or nonmetals.
a. gold
b. silicon
c. manganese
d. sulfur
e. barium
2. Which of the above elements are representative elements?
5-2 Apply using periodic table handout
III.
Atoms and Ions
- Each element is made up of atoms of the same kind
- All atoms are electrically neutral because protons = electrons
- When an atom loses or gains electrons it becomes a charged ion
- Ions are atoms or groups of atoms that have a positive or negative charge due to loss or gain of electrons
- Metallic atoms tend to lose electrons to become ions
- Na loses an electron when it combines so it has a positive charge of 1+
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Any atom or group of atoms that gain a positive charge are called cations
Metallic atoms that become cations have the same name but are called cations instead of atoms
Li atom becomes Li+ cation
Their names stay the same, but their properties change when they become cations
Na atoms react explosively in water – Na+ cation is soluble in water
Nonmetallic atoms tend to gain electrons to form ions
Atoms or groups of atoms that gain one or more electron to become negative are called anions
Their names change and their properties change when they become anions
The name of the anion ends in ide
The Chlorine atom gains 1 electron to become a Chloride anion with a charge of 1-
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Write the symbol and name of the ion formed.
a. A strontium atom loses two electrons.
b. An iodine atom gains one electron.
C. Describe two ways in which an ion forms from an atom
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Demo Na and water -
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IV.
Ionic Charges of an Element
- In ionic compounds the net charge must always be zero
- To write chemical formulas for ionic compounds the ionic charges of the elements must be determined
(oxidation numbers)
- This can be done using the periodic table
- Metallic ions tend to lose electrons thus picking up a positive charge
- Group 1A,2A,and 3A charge = group number
- Group 1A – lose 1 electron to become +1 cations (Li, Na, K, Rb, Cs, Fr)
- Group 2A – lose 2 electrons to become +2 cations (Be, Mg, Ca, Sr, Ba)
- Group 3A – lose 3 electrons + 3 cation (Al)
- Nonmetals tend to gain electrons so they form negative anions
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V.
Their charge is negative and can be determined by subtracting their group number by 8
7A – gain 1 electron 7 - 8 = -1 (F, Cl, Br, I)
6A – gain 2 electrons 6 - 8 = -2 (O, S, Se)
5A – gain 3 electrons 5 - 8 = -3 (N, P)
4A and 8A elements generally do not form ions
4A C and Si form molecular compounds
8A are the noble gases
Hand out ion sheet
Some elements (mostly transition metals) have more than one ionic charge page 120 table 5.3 (Example Pb
+2 and Pb +4 – Sn +2 and Sn +4) (Except Ag +1 and Zn +2 are transitions with only 1 ionic charge)
A roman numeral in parentheses is used in part of the name to indicate the charge of the element with more
than one oxidation number (stock system)
Lead (II) or Lead (IV) Tin (II) or Tin (IV) – If only one oxidation number no Roman Numeral in Name Aluminum (III)
Classical system uses the root word and suffixes at the end of the word (ous - lower ic – higher) ferrous would be Iron
(II) ferric would be Iron (III)
Practice
What is the charge of the ion of each of the following elements? (For metals with more than one common
ionic charge, the number of electrons lost is indicated.) a. sulfur
b. lead, four electrons lost
c. zinc d. argon e. bromine
I. copper, one electron lost.
Name the ions in Example above. List each as a cation or an anion.
Do 5-2 hw ions using periodic table and ion sheet
Polyatomic Ions
- Monatomic ions are formed from single atoms gaining or losing one or more electrons
- Polyatomic ions are tightly bound groups of atoms that behave as a unit and carry a charge (radicals)
- Polyatomic ions form by combining with monatomic ions or other polyatomic ions
- Polyatomic ions carry a charge so they are not found free in nature they are only found within compounds in
combinations that neutralize them
- Most polyatomic ions name end in either ite or ate
- The ite ending indicates one less O than the ate
- Write the symbol for each ion. Be sure to include the charge.
a. oxide ion
b. lead (II) ion c. lithium ion
d. nitride ion
e. cupric ion
f. fluoride ion
- Name the following ions. a. Ba2+
VI.
b. I-
c. Ag+
d. Hg2+
e. P3-
f . Sn4+
- Exceptions to this are ium ammonium, ide in cyanide and hydroxide
- Handout Polyatomic Hw Sheet 5-7
- List below polyatomic ion that has a -1 charge and is composed of 1O and 1 H
- List below polyatomic that has a +1 charge and is composed of 1 N and 4 H
- List below a polyatomic that behaves like group 6A anions
Compounds
- Compounds are formed by the chemical combination of two or more elements
- A molecule is an electrically neutral group of atoms that act as one
- Molecules of a given compound are identical, but they are different than molecules from another compound
- Compounds that are composed of molecules are molecular compounds
- Molecules are the smallest part of molecular compound that has all the properties of that compound
- Molecular compounds form when atoms share electrons (covalent bonding) usually formed by the sharing of
two nonmetallic elements
- Properties: relatively low melting and boiling point, most exist as gases or liquids at room temperature
(generally weaker bonds) (nonmetals to nonmetals)
- Example H2O – periodic table 354
- When metals and nonmetals combine to form compounds they usually form ionic compounds (ionic bonding)
- Ionic bonding involves the exchange of electrons between atoms
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Ionic compounds are usually composed of positive cations and negative anions
Ionic compounds are made up of charged particles but like molecular compounds they are electrically neutral
Most ionic compounds are crystalline solids at room temperature - high melting points Ex. NaCl (generally
stronger bonds)
Page 112 concept practice 5 and 6
Demo 5.3 page 106B
VII.
Chemical Formulas
- Due to the endless number of compounds chemists use chemical formulas to identify compounds
- A chemical formula shows the kinds and numbers of atoms in the smallest representative unit of the
substance, it also shows the ratio of one type of element to another in the compound
- Types of Chemical formulas
- Molecular formula shows the number and kinds of atoms present in a molecule of a compound Ex. H 2O (2
nonmetals)
- Diatomic molecules contain two atoms of the same atom
- There are 7 diatomic molecules H2 N2 O2 F2 Br2 Cl2 I2
- Structural formula tells the number and kinds of atoms along with how they are arranged and connected page
113
- Some compounds have the same molecular formula but may have different structural formula (isomers)
Hydrocarbons – octane C8H18
- To represent a ionic compound a formula unit is used
- A formula unit is the ratio that describes how many and what ions are present in the ionic compound
- Ionic charges are used to determine the ratio of the ions in the ionic compound
- Identify the number and kinds of atoms present in a molecule of each compound.
- a. ascorbic acid (vitamin C), C6H8O6 b. monosodium glutamate (MSG), C5H8O4NNa c. sucrose
(table sugar), C12H22O11 d. trinitrotoluene (TNT), C7H5N3O6 e. ammonium nitrate (a fertilizer),
NH4NO3
- Would you expect the following pairs of atoms to combine chemically to give an ionic or a
molecular compound? a. Li and S b. O and S
c. Al and O
d. F and Cl
e. I and K
f.
H and N
VIII.
Common and Systematic Names
- Compounds were often named according to some physical or chemical property of the compound (potash
K2CO3 , laughing gas N2O, rust, water, salt)
- Common names are very descriptive but they do not identify which elements are present in the compound
- It would also be impossible to memorize the 10 million common names of the compounds
- Common names mean different things to different people (location)
- The systematic method of naming chemical compounds is generally used to name inorganic compounds or
compounds that do not contain carbon
- Page 124 concept practice 16
- Quiz 5.2
Writing Chemical Formulas for Binary Ionic Compounds
- Binary compounds are composed of two elements that have to cancel each others charge out
- The positive charge on the cation must be equal to the negative charge on the anion so the net charge will be
zero on the ionic compound
- Rules for writing formulas
- 1. Write the symbol for the cation
- 2. Write symbol for anion
- 3. Identify oxidation numbers (charges) on the ions
- 4. Add subscripts to balance charges
- Crisscross method can be used to determine subscripts
- If same number cancel each other out - Reduce if need be – never write a 1
- Page 126 example 5 – concept practice 17 – practice problem 18
IX.
X.
Naming Binary Ionic Compound
- Rules
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1. Write the name of the cation
2. Write the root word of the anion
3. Add the ending ide to the root
4. If the ions have more than one oxidation number
- A. Determine which ion it is by balancing the charges
- B. Add the roman numeral in parentheses to indicate the oxidation number
Page 128 example 6 - concept practice 19 – practice problem 20
XI.
Ternary Ionic Compounds
- Ternary compounds contain atoms of three different elements – usually contain polyatomic
- Rules for writing formulas:
- 1. Write the symbol or formula of the cation
- 2. Write the symbol or formula of the anion
- 3. Identify oxidation numbers (charges) on the ions
- 4. Add subscripts to balance charges – if subscript is added to polyatomic parentheses must be used around
polyatomic
- Crisscross method can be used to determine subscripts – no 1’s - reduce
- Rules for writing names:
- 1. Write the name of the cation
- 2. Write the name of the anion
- 3. Use ite or ate to indicate polyatomic (except: hydroxide, cyanide)
- 4. If the ions have more than one oxidation number
- A. Determine which ion it is by balancing the charges
- B. Add the roman numeral in parentheses to indicate the oxidation number
- Page 130 example 8 practice problem 23 and 24
XII.
Binary molecular Compounds
- Binary molecular compounds are composed of two nonmetallic elements
- Binary molecular compounds are composed of molecules, so ionic charges are not used to assign formulas or
names to the compounds
- Binary molecular compounds often combine in more than one way example CO and CO 2
- Rules for naming:
- 1. Use prefix to indicate number of atoms of each element in each molecule – ion sheet bottom
- 2. Write name of first element (lowest electronegativity) farthest to left
- 3. Write root name of second element add ide
- 4. Vowel at end of prefix is dropped if same as the elements first vowel
- 5. If a single atom is in the first element no prefix is used
- Name these compounds N2O – PCl3 –AlCl3 – SF6
- Rules for writing formulas:
- 1. Write the symbol of the first element
- 2. Write the symbol of the second element
- 3. Use the prefixes to determine the subscripts of the atoms
- Carbon tetrabromide – dinitrogen tetrahydride – boron trichloride – diphosphorus trioxide
XIII.
Naming Common Acids
- Acids are compounds that give off hydrogen ions when dissolved in water
- The industrial strength of a country can be judged by how much acid it uses
- Acids are used in manufacturing, steel making, and fertilizers
- Common acids on ion sheet – bottom
- Go over hydrochloric and hydrofluoric
- Page 133 concept practice 28
XIV.
Summary of Naming and Formula Writing
1. Ionic compound net charge must be zero
2. Ide ending usually means binary compound
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3. Ite or ate ending usually means polyatomic
4. Prefixes in name usually mean molecular compound – show # of atoms
5. Roman numeral is used to show the ionic charge of the cation
- Page 134 practice problem 29 and 30
- Quiz 5.3
XV.
The Law of Definite Proportions (different elements in same compound)
- Law of definite proportions states in samples of any chemical compound the masses of elements are always
in the same proportions
- This means that in order to be considered a compound a substance must always contain the same elements
in exactly the same proportion by mass
- Example: In all hydrogen peroxide samples the mass ratio of hydrogen to oxygen is always 16:1 – 16g of O to
1g of H
- Water has a mass ratio of 8:1 – 8g of O to 1g of H
- Although hydrogen peroxide and water both only contain H and O they have very different properties, which is
due to the different mass ratios in which they are combined
- The law of definite proportions describes the mass ratios of the elements that make up the compound
XVI.
A the Law of Multiple Proportions (same elements in different compound))
- The Law of Multiple Proportions states that whenever two elements form more than one compound, the
different masses of one element that combine with the same mass of the other element are in the ratio of
small whole numbers
- Carbon reacts with oxygen to form 2 compounds. Compound A contains 2.41g carbon reacts with 3.22g of
oxygen. Compound B contains 6.71g of carbon for each 17.9g of oxygen. What is the lowest whole number
mass ratio of carbon that combines with the given mass of oxygen?
- Use law of definite proportions to find ratios – then compare ratios to find law of multiple proportions answer.
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