Chapter 20 Chemical Bonds

Ions Ex. Sodium: +11 – 10 = +1 p+ - e- = charge Atoms can gain or lose e- to form ions. Ion—an atom with a positive or negative charge. To find the charge, take the number of protons & subtract the number of electrons p+ - e- = charge Ex. Sodium: +11 – 10 = +1 Chlorine: +17 – 18 = -1

2 Types of Ions Cations—ions that have a + charge Form by atoms losing electrons Losing negative electrons makes it positive Metals form cations Anions—ions that have a – charge Form by atoms gaining electrons Nonmetals form anions

Ion Symbols Write the symbol of the element with its charge as a superscript A superscript is a small number in the upper right hand corner Ex. Na+1 & Cl-1 Polyatomic Ions—ions made of more than one atom. (ex. Sulfate: SO4-2) Chart on the back of your PT Write the symbol exactly as it is on the chart

Another casualty in the War of the Atoms.

Atomic Stability Atoms combine to form a compound that is more stable than the atoms alone Want to be like noble gases Noble gases are already stable and do not form compounds. Their outer energy level is full.

Rule Atoms gain, lose, or share electrons to get a full valence electron shell like the noble gases. H, He, Li, B, Be want 2 valence e- ALL other elements want 8 valence e- (an octet)

Ions & Bonding Atoms don’t gain or lose electrons on their own, it takes more than one. When an electron is lost by 1 atom it is gained by another. This makes an ionic bond Ex. Sodium has 1 valence e-Chlorine has 7, so it needs 1 more electron to be stable. If sodium gives its 1 valence e- to chlorine, they are both stable with 8 valence e-

Formulas Chemical Formula—tells what elements a compound contains & the number of atoms of each element. Ex. NaCl: 1 sodium atom & 1 chlorine atom A subscript is written after a symbol to tell how many atoms of that element there are. (unless there is just 1) MgCl2: 1 magnesium & 2 chlorines

Rules for Binary Ionic Formulas Binary = 2 different elements Write the metal cation 1st. Write the nonmetal anion 2nd. The net charge (overall charge) is zero. Na+1 Cl-1 = 0 Use subscripts to show multiple ions. Write the formula in the lowest whole number ratio. (reduce if needed)

Silver Chloride Cl-1 Ag+1 AgCl

Copper (I) Arsenide (Domeykite) Cu+1 As-3 Cu3As

Magnesium Sulfide Mg+2 S-2 MgS

Lead (IV) Sulfide (Galena) Pb+4 S-2 PbS2

Zinc Phosphide Zn+2 P-3 Zn3P2

A trick for ionic formulas Write both ions with their charges as superscripts. Crisscross the charges to make the subscripts in the formula Do not put + or – in the formula Cu3+ & O2- Cu2O3

Polyatomic Ions Ions that contain more than 1 element. Use parenthesis to indicate multiple polyatomic ions. Ex. Mg(NO3)2 Al(OH)3

Magnesium Sulfate Mg+2 SO4-2 MgSO4

Copper (II) Nitrate Cu+2 NO3-1 Cu(NO3)2

Strontium Hydroxide Sr+2 OH-1 Sr(OH)2

Ammonium Sulfide NH4+1 S-2 (NH4) 2S

Mistakes to Avoid Charges are not written in the formula Don’t drop polyatomic subscripts Hydroxide, OH, needs parentheses to indicate multiples. K+1Br-1 KBr CaNO2 Ca(NO3)2 CaOH2 Ca(OH)2

Write the cation name 1st Rules for Naming Binary Ionic with Group A Elements Write the cation name 1st Cation name is the same as the element name Write the anion name 2nd Change the ending of the element name to –ide. Ex. Oxygen becomes oxide Chlorine becomes chloride

Variable Charged Cations (transition & other metals) Same rules as for Group A, but… Name of the cation includes its charge as a Roman Numeral in parentheses Cu+2 = copper(II) Cu+1 = copper(I) (none are negative) No roman numerals are in formulas

Compounds Containing Polyatomic Ions Cation name: If the cation is a polyatomic ion, name it just as it is written on the back of your P.T. If cation is 1 element, use previous rules

Anion name: If the anion is a polyatomic ion, name it just as it is written on the back of your P.T. DO NOT change the ending. Most end in –ate or –ite If anion is 1 element, use previous rules

Ionic VS Covalent Ionic Electrons are transferred The bond is held together by the attraction between the + and - Covalent/Molecular Electrons are shared Atoms are physically attached by sharing electrons http://www.youtube.com/watch?v=_M9khs87xQ8&feature=youtu.be

Covalent/Molecular Compounds Ionic compounds contain a metal & a nonmetal Covalent: 2 or more nonmetals or metalloids Composed of molecules—NOT IONS—no charges!

Single, Double, & Triple Bonds Single Covalent Bond—2 shared electrons (1 pair) Double Covalent Bond—4 shared electrons (2 pairs) Triple Covalent Bond—6 shared electrons (3 pairs)

Covalent e- dot diagrams In e- dot diagrams a line represents a single bond A double line represents a double bond, and a triple line represents a triple bond + + +

Covalent/Molecular Compounds Unlike ionic compounds, 2 Nonmetals or Metalloids can combine in more than 1 way! CO2: the gas we breathe out. CO: colorless, odorless, deadly gas Both are carbon oxides, but it is important to distinguish between them.

Naming Covalent (Molecular) Compounds Prefixes tell the number of each element in the compound. The 2nd element: change the ending to -ide 1-mono 2-di 3-tri 4-tetra 5-penta 6-hexa 7-hepta 8-octa 9-nona 10-deca Examples: CO2 is carbon dioxide CO is carbon monoxide

IMPORTANT: The mono prefix is left off if the first element has 1 IMPORTANT: The mono prefix is left off if the first element has 1. Otherwise ALL parts of the name have a prefix. Sometimes the vowel at the end of a prefix is dropped so the name sounds better. Monoxide—not Monooxide

Formulas of Covalent Compounds The prefixes tell you the subscripts of elements in the formula. Example: tetraiodine octoxide I4O8 Do not reduce molecular formulas

Lets try some examples N2O PCl3 SF6 Dinitrogen monoxide Given the formula, name the following molecular compounds. N2O PCl3 SF6 CS2 C4O5 Dinitrogen monoxide Phosphorus trichloride Sulfur hexafluoride Carbon disulfide Tetracarbon pentoxide

More examples Carbon tetrafluoride Disulfur dichloride CF4 Given the name, what’s the formula for the following compounds. Carbon tetrafluoride Disulfur dichloride Dinitrogen tetroxide Phosphorus pentafluoride Trihydrogen Mononitride CF4 S2Cl2 N2O4 PF5 H3N

Ionic Covalent Type of elements Metal + Nonmetal (& polyatomic ions) 2 or more nonmetals/metalloids Smallest particle Ions (charges) Molecules (no charges) How bonds form Electrons are transferred Electrons are shared Formulas Balance the charges Use prefixes to tell subscripts Name Some have Roman Numerals Don’t change polyatomic ions 2nd element ends in –ide NO PREFIXES!! Prefixes tell how many 2nd element ends in -ide

Ionic or Covalent Quiz Number 1-10 and answer I or C Metal + Nonmetal Nonmetal + Nonmetal Metalloid + Nonmetal NO2 Mg(OH)2 NaI CH4 Calcium Phosphate Nitrogen trifluoride Sand (silicon dioxide)

Properties of Compounds When elements combine, the compounds are more stable than the elements alone. Compounds have different properties than their elements Na: soft metal, explodes in water Cl: toxic gas Salt (NaCl): edible crystal

Properties of Ionic & Covalent Ionic Bonds: held together by the attraction of a + and - charges Weak bonds Covalent Bonds: sharing electrons is a strong bond. (single, double, or triple) Can be Polar or Nonpolar

Polar vs Nonpolar Polar: is slightly (―) on one end & slightly (+) on the other. e- are pulled closer to the larger nucleus water is polar Nonpolar: e- are shared equally Oxygen gas (O2) is nonpolar