Chapter 6 Chemistry in Biology. Section 6.1 Atoms, Elements, & Compounds.
Elements and Compounds of Chemistry
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Transcript of Elements and Compounds of Chemistry
Elements and Compounds of
Chemistry
Naming and Formulas
The Periodic Table
The Periodic Table The most significant tool that chemists use
to organize and use chemical facts.
Properties of elements are organized into Groups: columns Periods: rows
Table Information Atomic number
Atomic symbol
Atomic weight (average)
Molecules Groups of atoms that are chemically
bonded Diatomic molecules: two atoms of the same
element H, N, F, O, I, Cl, Br (mnemonic device)
Molecular compounds: atoms to two or more different elements
Formulas Molecular formula: indicate the actual
numbers of atoms in a molecule Ex: C2H8
Empirical formula: give only the relative number of atoms of each type Ex: CH4
Structural Formula Molecular and empirical formulas do not
give any indication of how the atoms are linked or oriented to each other.
Structural formulas shows which are attached to which.
Ions Ions are electrically charged atoms
Cations: positively charged ions (Na+)
Anions: negatively charged ions (Cl-)
Polyatomic ions: atoms joined in a molecule that together carry a charge (OH-)
Predicting ionic charges Pattern: left side positively charged ions
Group 1: +1 Group 2:+ 2 Group 6: -2 Group 7: -1 Group 8: 0
Ionic Compounds Compounds composed of electrostatically
attracted cations and anions.
Typically made of metals (cations) and nonmetals (anions)
Molecular compounds are generally considered to be made of nonmetals.
Nomenclature There are more than 10 million known
chemical substances Chemists have created a standardized
system for naming compounds IUPAC Inorganic Organic
Names and Formulas of Ionic Compounds Naming cations (metals)
Rule: cations have the same name as the metal they came from
Some metals can form different charges, in this case add a roman numeral after the ion to represent the charge. Ex: Cu2+ (copper II ion)
Some cations are made from nonmetals and are polyatomic. Their names end in –ium
Ex: NH4+ (ammonium ion)
Naming Anions Rule: monatomic anions are named by
dropping the ending of the element and adding –ide Ex: H- hydride or F- flouride
Polyatomic ions that contain oxygen (oxyanions) have names that end in –ate or -ite
Naming ionic compounds Rule: names of ionic compounds are the
cation name followed by the anion name. Practice:
BaBr2
Al(NO3)3
FeCl3
Naming Binary Molecular Compounds Name the element farthest to the left on
the periodic table first If they are in the same group the lower
one is named first Change the ending of the second element
to –ide Greek prefixes are used to indicate the
number of atoms of each element present Mono is not used for the first element.
Practice IF5
XeO3
Dihydrogen monoxide Carbon tetrachloride Tetraphosphorus hexasulfide
The binary compounds of hydrogen are special cases. They were discovered before a convention was adopted and hence their original names have stayed.
Hydrogen forms binary compounds with almost all non-metals except the noble gases. Examples
HF - hydrogen fluorideHCl - hydrogen chloride H2S - hydrogen sulfide
Water H2O is not called dihydrogen monoxide
Binary compounds of Hydrogen
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When many hydrogen compounds are dissolve in water they take on the form of an acid. Special rules apply to acids. The “ite” suffix becomes “ous” and the “ate” suffix becomes “ic”
Acids
HCl Hydrochloric Acid Cl- Chloride
HNO2 Nitrous Acid NO2- Nitrite
HNO3 Nitric Acid NO3- Nitrate
H2SO3 Sulfurous Acid SO32- Sulfite
H2SO4 Sulfuric Acid SO42- Sulfate
H3PO3 Phosphorous Acid PO33- Phosphite
H3PO4 Phosphoric Acid PO43- Phosphate
H2CO3 Carbonic Acid CO32- Carbonate
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Chemical Reactions Elements and compounds frequently
undergo chemical reactions to form new substances
In a chemical reaction, chemical bonds are frequently broken and new chemical bonds are formed
Atoms are neither created nor destroyed in an ordinary chemical change
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Chemical Reactions A balanced chemical reaction is used to
describe the process that occurs in a chemical change.
For example: Zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas.
This chemical reaction could be written asZn + 2 HCl ZnCl2 + H2
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Reactants and Products In the chemical reaction
Zn + 2 HCl ZnCl2 + H2
Reactants Products
This shorthand way of describing a chemical reaction is known as a chemical equation
The starting materials are shown on the left and are known as reactants
The substances formed are shown on the right and are known as the products
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Balancing a Chemical Reaction A proper chemical reaction must be
balancedZn + 2 HCl ZnCl2 + H2
Reactants Products Each element must appear on both sides
of the arrow and equal number of times Chemical reactions can be balanced by
inserting numbers in front of formulas. These numbers are called coefficients
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Balancing Chemical Reactions Most simple equations can be balanced by
inspection Example: Balance the following equation
BaCl2 + K3PO4 Ba3 (PO4)2 + KCl
• There are 3 Ba on the right so we need coefficient of 3 in front of BaCl2
• There are 2 PO4 on the right so we need a coefficient of 2 in front of K3PO4.
• This leaves 6 K on the left so we need a coefficient of 6 in front of the KCl on the right
The balanced equation is
3 BaCl2 + 2 K3PO4 Ba3 (PO4)2 + 6 KCl
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Balancing Chemical Reactions An equation is balanced when there are the same
number and kind of atoms on both sides of the arrow
3 BaCl2 + 2 K3PO4 Ba3(PO4)2 + 6 KCl
Reactants (Left) Products (Right)
Ba 3 Ba 3
Cl 3 x 2 = 6 Cl 6
K 2 x 3 = 6 K 6
P 2 P 2
O 2 x 4 = 8 O 2 x 4 = 824
State Symbols State symbols are often added to chemical equations.
CaCO3 (s) + 2 HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l)
Symbols
(s) Solid
(l) Liquid
(g) Gas
(aq) Aqueous (Water Solution)
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Types of Reactions There are many kinds of chemical
reactions that occur. Some are very simple while others are very complex and may occur in multiple steps.
A number of reactions conform to some relatively simple patterns
Understanding and identifying these patterns can be helpful in predicting the products of similar reactions
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Direct Combination In a direct combination, two elements or
compounds combine to form a more complicated product
ExamplesCaO + CO2 CaCO3
2 H2 + O2 2 H2O
2 FeCl2 + Cl2 2 FeCl3 N2 + O2 2 NO
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Direct Combination In a direct combination, two elements or
compounds combine to form a more complicated product
ExamplesCaO + CO2 CaCO3
2 H2 + O2 2 H2O
2 FeCl2 + Cl2 2 FeCl3 N2 + O2 2 NO
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Single Replacement In a single replacement, one substance
(usually an element) takes the place of another in a compound
ExamplesZn + H2SO4 ZnSO4 + H2
Cl2 + 2 KBr 2 KCl + Br2
Mg + CuCl2 MgCl2 + Cu
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Double Replacement In a double replacement, two substances
exchange places in their respective compounds
ExamplesAgNO3 + NaCl AgCl + NaNO3
3 CaCl2 + 2 K3PO4 Ca3(PO4)2 + 6KCl BaCl2 + Na2SO4 BaSO4 + 2NaCl
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