Chemical Bonds

Atom – the smallest unit of matter “indivisible” Helium atom

electron shells Atomic number = number of Electrons Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells. Electron shells determine how an atom behaves when it encounters other atoms

Electrons are placed in shells according to rules: The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons C would like to N would like to O would like to Gain 4 electrons Gain 3 electrons Gain 2 electrons

Why are electrons important? Elements have different electron configurations different electron configurations mean different levels of bonding

Electron Dot Structures Symbols of atoms with dots to represent the valence-shell electrons 1 2 13 14 15 16 17 18 H He:            Li Be  B   C   N   O  : F  :Ne :                    Na Mg  Al  Si  P S :Cl  :Ar :        

Chemical bonds: an attempt to fill electron shells Ionic bonds – Covalent bonds – Metallic bonds

Learning Check A. X would be the electron dot formula for  A. X would be the electron dot formula for 1) Na 2) K 3) Al   B.  X  would be the electron dot formula 1) B 2) N 3) P

IONIC BOND bond formed between two ions by the transfer of electrons

Formation of Ions from Metals Ionic compounds result when metals react with nonmetals Metals lose electrons to match the number of valence electrons of their nearest noble gas Positive ions form when the number of electrons are less than the number of protons Group 1 metals  ion 1+ Group 2 metals  ion 2+ Group 13 metals  ion 3+

Formation of Sodium Ion Sodium atom Sodium ion Na  – e  Na + 2-8-1 2-8 ( = Ne) 11 p+ 11 p+ 11 e- 10 e- 0 1+

Formation of Magnesium Ion Magnesium atom Magnesium ion  Mg  – 2e  Mg2+ 2-8-2 2-8 (=Ne) 12 p+ 12 p+ 12 e- 10 e- 0 2+

Some Typical Ions with Positive Charges (Cations) Group 1 Group 2 Group 13 H+ Mg2+ Al3+ Li+ Ca2+ Na+ Sr2+ K+ Ba2+

Learning Check A. Number of valence electrons in aluminum 1) 1 e- 2) 2 e- 3) 3 e- B. Change in electrons for octet 1) lose 3e- 2) gain 3 e- 3) gain 5 e- C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+

Solution A. Number of valence electrons in aluminum 3) 3 e- B. Change in electrons for octet 1) lose 3e- C. Ionic charge of aluminum 3) 3+

Learning Check Give the ionic charge for each of the following: A. 12 p+ and 10 e- 1) 0 2) 2+ 3) 2- B. 50p+ and 46 e- 1) 2+ 2) 4+ 3) 4- C. 15 p+ and 18e- 2) 3+ 2) 3- 3) 5-

Ions from Nonmetal Ions In ionic compounds, nonmetals in 15, 16, and 17 gain electrons from metals Nonmetal add electrons to achieve the octet arrangement Nonmetal ionic charge: 3-, 2-, or 1-

Fluoride Ion     1 - : F  + e : F :     2-7 2-8 (= Ne) unpaired electron octet     1 - : F  + e : F :     2-7 2-8 (= Ne) 9 p+ 9 p+ 9 e- 10 e- 0 1 - ionic charge

Ionic Bond Between atoms of metals and nonmetals with very different electronegativity Bond formed by transfer of electrons Produce charged ions all states. Conductors and have high melting point. Examples; NaCl, CaCl2, K2O

Ionic Bonds: One Big Greedy Thief Dog!

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

COVALENT BOND bond formed by the sharing of electrons

Covalent Bond Between nonmetallic elements of similar electronegativity. Formed by sharing electron pairs Stable non-ionizing particles, they are not conductors at any state Examples; O2, CO2, C2H6, H2O, SiC

Covalent Bonds

Bonds in all the polyatomic ions and diatomics are all covalent bonds

when electrons are shared equally NONPOLAR COVALENT BONDS when electrons are shared equally H2 or Cl2

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)

when electrons are shared but shared unequally POLAR COVALENT BONDS when electrons are shared but shared unequally H2O

Polar Covalent Bonds: Unevenly matched, but willing to share.

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

Hydrogen Bond “Hydrogen bond" implies, one part of the bond involves a hydrogen atom. The hydrogen must be attached to a strongly electronegative heteroatom, such as oxygen, nitrogen or fluorine, which is called the hydrogen-bond donor.

METALLIC BOND bond found in metals; holds metal atoms together very strongly

Metallic Bond Formed between atoms of metallic elements Electron cloud around atoms Good conductors at all states, lustrous, very high melting points Examples; Na, Fe, Al, Au, Co

Metallic Bonds: Mellow dogs with plenty of bones to go around.

Ionic Bond, A Sea of Electrons

Metals Form Alloys Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal. Examples are steel, brass, bronze and pewter.

Formula Weights Formula weight is the sum of the atomic masses. Example- CO2 Mass, C + O + O 12.011 + 15.994 + 15.994 43.999

Practice What is the type of bond and what is the formula weight? Na2O CH4 CO2 K2O MgO

Practice Compute the mass of the following compounds round to nearest tenth & state type of bond: NaCl; 23 + 35 = 58; Ionic Bond C2H6; 24 + 6 = 30; Covalent Bond Na(CO3)2; 23 + 2(12 + 3x16) = 123; Ionic & Covalent

Formulas and Names of Binary Metal-Nonmetal Compounds The name of the metal is first (ie: NaCl, sodium chloride) The name of the nonmetal has -ide added (ie: NaCl sodium chloride) IF the metal has more than one possible charge -indicate which ion using the charge in roman numerals (ie: FeCl2 Iron (II) chloride).

Cu2S Name the first ion. Since it is a transition metal, you must use a Roman Numeral. Which Roman Numeral? The Roman Numeral is the same as the charge of the ion. How do you find the charge? Deductive reasoning! All compounds are neutral Sulfur has a -2 charge (group 16) There are two coppers. Therefore each copper must have a +1 charge for all ions to be neutral Copper I Sulfide

Another Example: MnO2 Name the first ion. Since it is a transition metal, you must use a Roman Numeral. How do you determine the Roman Numeral? It is the same as the charge. What is the charge of Mn? All compounds are neutral. Oxygen (group 16) has a -2 charge. There are two oxygens and one Mn. Therefore Mn must have a +4 charge for this compound to be neutral. Manganese IV oxide

You need to remember the charges for these. There are three transition elements which do not require a Roman Numeral because they have single definite charges. These are Zinc – Zn+2 Cadmium – Cd+2 Silver – Ag+1 You need to remember the charges for these. No Roman Numerals needed for these. Ag2O Name the first ion. Name the second ion changing the suffix to –ide. Silver oxide ZnCl2 Name the first ion. Zinc chloride Name the second ion changing the suffix to –ide.

How do you write formulas for binary ionic compounds given the name? Two simple steps: Write the symbol and charge of each ion Balance the charges by providing subscripts to tell how many of each atom is present. Magnesium chloride Mg+2 Cl-1 Cl-1 You need a second Cl-1 to balance the charges MgCl2

FeBr3 More examples: Iron III bromide Write the symbol and charge of each ion. The charge of the iron is provided by the Roman Numeral. Fe+3 Br -1 Br -1 Br -1 FeBr3 Balance the charges by supplying subscripts. The subscripts tell how many of each ion is needed to balance the compound. You’ll need three bromine ions to balance the one iron.

Al2S3 Aluminum Sulfide Write the symbol and charge of each ion. Balance the charges by supplying subscripts. S-2 In this case the charges do not evenly divide into each other. You must find the least common multiple. SIX Al2S3 How many aluminums are needed to arrive at a +6 charge? 2 How many sulfurs are needed to arrive at a -6 charge? 3

You need to learn these!!! CO3-2 carbonate This ion is composed of one carbon and three oxygens and the entire group has a charge of -2. Polyatomic ion – Group of atoms that act as a unit and carry a charge. More examples: PO4-3 Phosphate C2H3O2-1 Acetate SO4-2 Sulfate OH-1 Hydroxide SO3-2 Sulfite NO3-1 Nitrate ClO4-1 Perchlorate NO2-1 Nitrite ClO3-1 Chlorate NH4+1 Ammonium (only positive PI) ClO2-1 Chlorite ClO-1 Hypochlorite You need to learn these!!!

A few more examples: Fe(OH)3 Name the first ion. Iron III hydroxide Remember that iron requires a Roman Numeral since it is a transition element. What Roman Numeral should be used? Since there are 3 OH groups, each with a -1 charge, the charge of the iron must be +3 for the compound to be neutral The Roman Numeral comes from the charge of the ion. How do you find the charge of the iron? You know two things: All compounds are neutral. You know the charge of OH (-1) Name the polyatomic ion.

NH4Cl Name the first ion. Ammonium chloride Name the second ion. Notice that since the second ion is a nonmetal that, like binary ionic compounds, the suffix of the nonmetal changes to –ide. Name the first ion. (NH4)3PO4 Ammonium phosphate Name the second ion. Looks like a monster, but it’s really a pussycat.

ONE more example: Cu2SO4 Name the first ion. You should realize that you need a Roman Numeral since copper is a transition metal. Copper I sulfate The Roman Numeral is the same as the charge. What is the charge? The charge of sulfate is -2. Since there are two coppers, the charge of the copper must be +1. Name the second ion.

Naming – you must use prefixes. 1 = mono 3 = tri 5 = penta 7 = hepta 9 = nona 2 = di 4 = tetra 6 = hexa 8 = octa 10 = deca Steps The first nonmetal only gets a numeric prefix when there is more than one. No prefix if there is only one. The second element always gets a numeric prefix and always has a suffix of -ide

Dinitrogen tetraoxide H2O Dihydrogen monoxide CCl4 CO2 Carbon dioxide CO Carbon monoxide N2O4 Dinitrogen tetraoxide H2O Dihydrogen monoxide CCl4 Carbon tetrachloride Name the first element. Since there is only one, no prefix is needed. The second element always gets a prefix and a suffix of –ide. Name the first element. Since there are two present, the prefix “di” is needed. The second element always gets a prefix and a suffix of –ide.

AlCl3 What do you think about this one??? Be careful. This is a metal and nonmetal. Always keep your Periodic Table in front of you for reference. You may have been tempted to say “aluminum trichloride”. This is INCORRECT! This is a binary IONIC compound. No prefixes are used. Simply aluminum chloride. Given the names of binary molecular compounds, how do you write the formulas? Very easy to do!!! The prefixes tell you how to write the formulas. DO NOT CONSIDER CHARGES. NONMETALS ARE ALL NEGATIVE SO TO USE CHARGES DOES NOT WORK!

SiO2 P2Cl5 Silicon dioxide Diphosphorous pentachloride Silicon and oxygen are both nonmetals. The lack of a prefix on silicon means that there is only ONE silicon. The prefix “di” in front of oxide means that there are TWO oxygens. SiO2 Diphosphorous pentachloride P2Cl5 Phosphorous and chloride are both nonmetals. The prefix “di” means that there are TWO phosphorouses (Is that a word?) The prefix “penta” before chlorine means that there are five chlorines.

NO Is this not sooooooo easy!?? Nitrogen monoxide Nitrogen and oxygen are both nonmetals. The lack of a prefix on nitrogen means only ONE nitrogen. The prefix “mono” on oxygen indicates ONE oxygen. NO Is this not sooooooo easy!??

Let’s Practice Ca(OH)2 Calcium hydroxide SO2 Sulfur dioxide (NH4)3PO4 Ammonium phosphate Co2(CO3)3 Cobalt (III) carbonate HBr Hydrobromic acid Ternary Ionic Binary molecular Ternary Ionic Ternary Ionic Binary acid

Potassium acetate KC2H3O2 Cadmium nitrate Cd(NO3)2 Aluminum oxide Al2O3 Hydrosulfuric acid H2S Difluorine trioxide F2O3 Ternary Ionic Ternary Ionic Binary Ionic Binary acid Binary molecular