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Section 1—Stability in Bonding. Chapter 19— CHEMICAL BONDS. Why is the Statue of Liberty Green?. Copper, Sulfur, and Oxygen.
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Section 1—Stability in Bonding Chapter 19— CHEMICAL BONDS
Copper, Sulfur, and Oxygen • Some of the matter around you is in the form of uncombined element, such as copper, sulfur, and oxygen. But, like many other sets of elements, these 3 elements unite chemically to form a compound when the conditions are right. • The green coating on the Statue of Liberty and some old pennies is a result of this chemical change.
Copper Sulfate (Copper + Sulfur + Oxygen) • One compound in this coating, is a new compound called copper sulfate. • Copper sulfate isn’t shiny and copper colored like elemental copper. Nor is it a pale-yellow solid like sulfur or a colorless, odorless gas like oxygen. • Copper sulfate has its own unique properties.
Example—Sodium + Chlorine = Salt (Sodium Chloride) Sodium (shiny, soft, silvery metal) Chlorine (poisonous greenish-yellow gas)
Sodium(Na) + Chlorine(Cl) = Sodium Chloride(NaCl—Chemical Formula) or Table Salt
CHEMICAL FORMULA • A chemical formula tells what elements a compound contains and the exact number ofatoms of each element in a unit of that compound. • EXAMPLE—H2O =CHEMICAL FORMULA • H=hydrogen; O=oxygen; and a subscript of 2 = 2 atoms of hydrogen and if no subscript = 1 atom of oxygen
Example—BATTERY ACID OR SULFURIC ACID • H2SO4 = • 2 hydrogen atoms • 1 sulfur atom • 4 oxygen atoms
ATOMIC STABILITY • Why do atoms form compounds? • Atoms combine when the compound formed is more STABLE than the separate atoms. • 115 elements—MOST combine with other elements • GROUP 18—the 6 NOBLE GASES seldom form compounds. WHY?
ATOMS OF GROUP-18 ARE UNUSUALLY STABLE • These elements all have 8 electrons in their outer energy level, giving them a COMPLETE outer energy level. EXCEPT He—only 2 electrons, but a COMPLETE outer energy level. • An atom is chemically stable (will not form compounds) when its outer energy level is COMPLETE. • He = 2 outer electrons • Ne = 8 outer electrons • Ar = 8 outer electrons
The Noble Gases are STABLE because they each have a COMPLETE outer energy level.
How do the ELECTRON DOT DIAGRAMS represent other elements? • How does that relate to their ability to make compounds? • HYDROGEN contains 1 electron in its 1 energy level. (INcomplete, UNstable) • This is why so many hydrogen containing compounds, including WATER exist on Earth.
HELIUM • In contrast, helium’s outer energy level contains 2 electrons. • Helium already has a full outer energy level by itself and is COMPLETE and STABLE. • Helium rarely forms compounds, but, by itself, the element is a commonly used gas.
How does hydrogen or any other element find or get rid of extra electrons? • Atoms with INcompleteouter energy levels can lose, gain, or share electrons to obtain a STABLE outer energy level. • They do this by combining with other atoms that also have partially complete outer energy levels. • RESULT: Each achieve stability.
EXAMPLE—SODIUM AND CHLORINE • Sodium--GROUP 1 • 1 electron in its outer energy level • (INCOMPLETE, UNSTABLE) • Chlorine—GROUP 17 • 7 electrons in its outer energy level • (INCOMPLETE, UNSTABLE)
SODIUM AND CHLORINE • When these atoms combine, sodium loses 1 electron and chlorine gains 1 electron. • RESULT: Sodium and chlorine both receive a COMPLETE and STABLE outer energy level.
EXAMPLE—HYDROGEN AND OXYGEN • In the compound water, each hydrogen atom needs 1 electron to fill its outer energy level. • The oxygen atom needs 2 electrons for its outer energy level to be stable with 8 electrons. • HYDROGEN and OXYGEN share electrons instead of gaining or losing electrons.
WATER—H2O When atoms gain, lose, or share electrons, an attraction forms between the atoms, pulling them together to form a compound. This attraction or force that holds atoms together is a CHEMICAL BOND.
Section 2—TYPES OF BONDS Chapter 19: CHEMICAL BONDS
What is an ION? • An atom that has LOST or GAINED electrons is called an ion. • An ion is a charged particle, because it now has either MORE or LESS ELECTRONS than protons. • The POSITIVE and NEGATIVE charges are NOT BALANCED. • BEFORE (INDIVIDUAL ELEMENTS): PROTONS = ELECTRONS • NOW (GETTING READY TO FORM COMPOUNDS): PROTONS ≠ ELECTRONS
EXAMPLE---NaCl (SALT) • Some of the most common compounds are made by the LOSS and GAIN of just 1 ELECTRON. (Group 1 element + Group 17 element) Ex. NaCl • Examples…Sodium chloride (table salt); sodium fluoride (anticavity ingredient in toothpaste); and potassium iodide (ingredient in iodized salt)
What happens when sodium and fluorine atoms come together? • Na LOSES AN ELECTRON Na+ • (1 LESS ELECTRON = POSITIVE CHARGE) • The 1+ charge is shown as a superscript written AFTER the element’s symbol, Na+, to indicate its charge. • F GAINS AN ELECTRON F- • (1 MORE ELECTRON = NEGATIVE CHARGE) • RESULT: The compound has a neutral charge, because positive and negative charges of the ions cancel each other. Ex. NaF (Another Ex. Na+ and Cl- NaCl )
The IONIC Bond • An ionic bond is a force of attraction between the opposite charges of the ions in an ionic compound. (Metal + Nonmetal) • Ionic bond with more than 1 electron involved… MgCl2 MagnesiumGroup 2 and ChlorineGroup 17
When magnesium reacts with chlorine, a magnesium atom LOSES 2 electrons and becomes a POSITIVE charged ion, Mg2+. • At the same time, 2 chlorine atoms GAIN 1 electron each and become NEGATIVE charged ions, Cl-. • A MAGNESIUM atom has 2 electrons to LEND, but a single CHLORINE atom needs to BORROW only 1 electron. • Therefore, it takes 2 chlorine atoms to take the 2 electrons from the 1 magnesium ion.
MgCl2 (Compound is neutral ) • Magnesium LOSES 2 electrons = Mg2+ • 2 Chlorine atoms GAIN 2 electrons = Cl- Cl- (Each Cl atom GAINS 1 electron)
ZERO NET CHARGE • The POSITIVE CHARGE of the 1 magnesium ion is exactly EQUAL to the NEGATIVE CHARGE of the 2 chloride ions. • ***Therefore, the compound is NEUTRAL. • ***Ionic bonds usually are formed by bonding between METALSand NONMETALS(losing/gaining electrons). • (Examples: NaCl and MgCl2)
SHARING ELECTRONS • Some atoms of NONMETALS are unlikely to LOSE or GAIN electrons. • For example, the elements in GROUP 14 have 4 electrons in their outer energy level. They would have to lose or gain 4 electrons in order to have a stable outer energy level. • The loss of this many electrons takes a great deal of energy. Each time an electron is removed, the nucleus holds the remaining electrons even more tightly.
COVALENT BOND • The attraction that forms between atoms when they SHARE electrons is known as a covalent bond. • A neutral particle that forms as a result of electron sharing is called a molecule. • O = 6 electrons • H = 1 electron • H = 1 electron • 2 SINGLE COVALENT BONDS
COVALENT BONDS (N2, O2) • N = 5 electrons • N = 5 electrons ***3 pairs of electrons represent 3 bonds • O = 6 electrons • O = 6 electrons ***2 pairs of electrons represent 2 bonds
UNEQUAL SHARING • Electrons are not always shared equally between atoms in a covalent bond. • The strength of the attraction of each atom ot its electrons is related to… • SIZE of the atom • CHARGE of the nucleus • TOTAL NUMBER OF ELECTRONS the atom contains
This type of molecule is called polar. A polar molecule is one that has a slightly positive end and a slightly negative end, although the overall charge is NEUTRAL.
A nonpolar molecule is one in which electrons are shared equally in bonds. • C = 4 electrons • Cl = 7 electrons ***4 Chlorine atoms needed to equally share electrons, so that carbon and chlorine all have 8 electrons in their outer energy levels. • CCl4 • This type of molecule does not have oppositely charged ends.
Section 3—WRITING FORMULAS AND NAMING COMPOUNDS Chapter 19—CHEMICAL BONDS
WRITING FORMULAS • The first formulas of compounds you will write are for binary ionic compounds. • A binary compound is a compound that is composed of 2 elements. • EXAMPLE—Potassium iodide, the salt additive, is a binary ionic compound.
WRITING FORMULAS • What do you need to know before you can write the formula? • Which ELEMENTS are involved? • What NUMBER OF ELECTRONS are lost, gained, or shared? (IN ORDER TO BECOME STABLE)
OXIDATION NUMBER = CHARGE OF THE ION • An OXIDATION NUMBER tells you how many electrons an atom has GAINED, LOST, or SHARED to become stable. (p. 588) • For ionic compounds, the OXIDATION NUMBER is the same as the CHARGE OF THE ION.
EXAMPLE—Sodium (Na) and Chlorine (Cl) CHARGEOX. # Na ion = 1+ 1+ Cl ion = 1- 1- • Na = G-1, 1 outer electron (LOSES 1 ELECTRON OR LOSES 1 NEG—CHARGE IS POS) • Cl = G-17, 7 outer electrons (GAINS 1 ELECTRON OR GAINS 1 NEG—CHARGE IS NEG)
COMPOUNDS ARE NEUTRAL • Although the individual IONS in a compound carry CHARGES, the COMPOUND itself is NEUTRAL. • ***A formula must have the right number of POSITIVE IONS and the right number of NEGATIVE IONS so the charges BALANCE. • EXAMPLE…Sodium chloride (NaCl) • Na+ 1+ • Cl- 1- 0 (Compound is neutral/0 charge)
CALCIUM FLUORIDE • Ca2+ = 2+ • F1- = 1- • In this case, you need to have 2 fluoride ions for every calcium ion in order for the charges to cancel and the compound to be NEUTRAL. • CaF • 2+ + 1- • 2+ + 2(1-) • 2+ + 2- =0 (COMPOUND IS NEUTRAL) • 1 ATOM OF Ca and 2 ATOMS OF F; CaF2
Aluminum Oxide • Al3+ = 3+ • O2- = 2- • What is the least common multiple of 3 and 2? • 6 (2 x 3) • 2 Al ions and 3 O ions are needed in order to have a 6+ charge and a 6- charge IONSCHARGES Al= 2 x 3+ = 6+ O= 3 x 2- = 6- 0 • Therefore, the nuetral compound = • Al2O3
RULES FOR WRITING FORMULAS—Sodium Chloride • Write the symbol of the element or polyatomic ion (ions with more than 1 atom)that has a positive oxidation number or charge. Ex. Na ***H, ammonium ion (NH4), and all metals have positive oxidation numbers. Ex. Na = metal = + • Write the symbol of the element or polyatomic ion with the negative oxidation number. Ex. Cl ***Nonmetals (other than H) and polyatomic ions (other than NH4) have negative oxidation numbers. Ex. Cl = nonmetal = -
RULES FOR WRITING FORMULAS—(CONTINUED) • Use subscripts next to each ion so that the sum of the charges is ZERO. CHARGE Na ion = 1+ Cl ion = 1- Ex. Therefore, 1 atom of sodium and 1 atom of chlorine is needed…NaCl
COMPOUNDS WITH COMPLEX IONS • Not all compounds are binary (contain 2 elements). Baking soda, used in cooking, has the formula: • NaHCO3 • Which 4 elements does it contain? • Na = sodium H = hydrogen • C = carbon O = oxygen
Some compounds, including baking soda, are composed of more than 2 elements. They contain polyatomic ions. • poly = many • polyatomic = many atoms • A polyatomic ion is a positively or negatively charged covalently (nonmetals) bonded group of atoms.
RULES FOR WRITING NAMES—BaF2 • You can name a binary ionic compound (2 elements—1 metal and 1 nonmetal) • (Using TABLE 2-p.588, check to see if the positive ion is capable of forming more than 1 oxidation number.) Write the name of the positive ion (METAL). Ex. Barium
RULES FOR WRITING NAMES—(CONTINUED) • Write the root name of the negative ion (NONMETAL). The root is the first part of the element’s name. (chlorine = chlor-; oxygen = ox) Ex. Fluorine = fluor • Add the ending –ide to the root. Ex. BaF2 = Barium fluoride
RULES FOR WRITING NAMES—POLYATOMIC IONS—Ex. NaHCO3 • The polyatomic ion in baking soda is the hydrogen carbonate ion. (HCO3-) • To name a compound that contains one of these ions… • Write the name of the positive ion (METAL). Ex. Sodium • Write the name of the negative ion (NONMETALS) TABLE 4—P.591-Hydrogen carbonate (Sodium hydrogen carbonate)
POLYATOMIC ION—EX. K2SO4 • Potassium sulfate • WRITING FORMULAS FOR COMPOUNDS CONTAINING POLYATOMIC IONS, FOLLOW THE RULES FOR BINARY COMPOUNDS, WITH 1 ADDITION. • ***When more than 1 polyatomic ion is needed, write parentheses around them before adding the subscript…