4Compounds, not elements, determines most of what we experience in this world How elements bond together in compounds determines the properties of matter that we observeMany of the elements that we observe in nature are poisonous in their natural form, but as compounds, they sustain and enable lifeIonic compounds, unlike covalent compounds, dissociates in water to form positive and negative ionsCovalent compounds remain as whole units when dissolved in waterMetals form special bonds that are neither ionic or covalent, but somewhere in the middleMetals conduct electricity because their valence electrons are not fixed and can move from atom to atom
5Sulfur can help life because it is an essential nutrient and is found in amino acids Sulfur also causes the foul smell in garlic, rotten eggs and in skunksIron is important to many body functions including the transferring of oxygen from lungs to the cells (hemoglobin)Iron is also magnetic in nature and when the two (iron and sulfur) are mixed they each maintain their physical and chemical properties, until both are heated close to the melting point of steel (where a chemical reaction occurs)The resulting compound is iron sulfide and no longer has the properties of iron or sulfur, but new properties
6What is a chemical bond?Using a molecule building kit, a chemical bond is a stick and atoms joined togetherThe sticks between the atoms represent bonds between each atomInside the atom are positive and negative charges that attract and repel each other (protons repel other protons and electrons repel each other)There are also intermolecular forces, forces between one atom and another atom or atomsBecause of protons of one atom attracting electrons of another atom, there is an array of charges that each atom has to deal with which can cause a shift in atomic chargesPolarization is an uneven distribution of positive or negative charge that occurs when anything (like other atoms) creates an charge outside of the atom (this is how bonds form)
7That distortion is called polarization. The electron cloud responds to changes in the electromagnetic environment.That distortion is called polarization.
8What happens when two hydrogen atoms approach each other? Each nucleus attracts the electron cloud of the other atom.Each nucleus repels the other nucleus.The electron cloud repels the other electron cloud.At a certain distance there is an equilibrium between attractive and repulsive forces.
9In nonpolar covalent bonds, the difference between the electronegativity of both atoms is very little (between 0.3 and 0.0)In polar covalent bonds the difference between the electronegativity of both atoms is a moderate difference (between 1.7 and 0.3)In ionic bonds the difference between the electronegativity of both atoms is a large difference (between 3.3 and 1.7)
10Covalent bond is formed when atoms share electrons (sometimes the sharing is equal, sometimes it is not equal sharing)Ionic bonds are formed when metals give 1, 2, or three electrons to a nonmetal (each atom becomes charged (as positive or negative)In a non-polar covalent bond, the sharing of electrons is equal so the electrons are evenly distributed so there is little charge separation on the surface of the moleculeIn a polar covalent bond, the uneven sharing of electrons creates a region that is more positive, and another area that is more positive than the opposite end.Metallic bonds both atoms have a low electronegativity and low ionization energy so they don’t attract each other’s electrons very wellAs a result of metallic bonding, a bunch of atoms share electrons
11Assignment Take a new sheet of paper and fold it into three sections Write your name, the title of the chapter and the numberOn the first section from the sheet of paper, please write six things that you learned from your notes so far that could appear on your test.
12Sometimes when two or more molecules combine the result can be a polar or non polar molecule, even though individual bonds are polarThe reason for this is because when a molecule is called polar, the overall molecule is polar and not just certain bonds (the surface of the molecule can be non polar, even though is has polar bonds)
13When a chemical bond is formed, some valence electrons are either shared or transferred between atomsOnly unpaired unshared electrons can participate in chemical bondsIt is important to know that in the outer shell, the 5th, 6th and 7th valence electrons pair up and reduce the amount of electrons available to take part in chemical bondingThe number of valence electrons affects bond number and ion chargeIn a molecular compound, each unpaired unshared valence electron can form one covalent chemical bondExample: both nitrogen and phosphorous atoms have three unpaired valence electrons (so they can form three covalent bonds)All atoms react chemically to reach the octet configuration
14Atoms are neutral charge but unpaired unshared electrons can cause atoms to become positive or negative ions by the gaining or loss of electronsWhen an atom (metal) loses one or more electrons, it becomes a positive ion with a “+” 1, 2, or 3 chargeGroup 1 metals lose 1 electron to become a +1 ionGroup 2 metals lose 2 electron to become a +2 ionGroup 13 metals lose 3 electron to become a +3 ionWhen an atom (nonmetal) gains one or more electrons, it becomes a negative ion with a “-” 1, 2, or 3 chargeGroup 17 metals gain 1 electron to become a -1 ionGroup 16 metals gain 2 electron to become a -2 ionGroup 15 metals gain 3 electron to become a -3 ion
15A covalent bond An ionic bond Electrons are shared between the two nuclei.One or more electrons are transferred to form ions.The positive and negative ions attract each other.
16Some atoms are more greedy for electrons than others! Electrons are unevenly shared between oxygen and hydrogen.
17Oxygen is slightly more electronegative than hydrogen. Electronegativity(electron sharing)Oxygen is slightly more electronegative than hydrogen.This results in uneven sharing of electrons.
18Types of bond Nonpolar covalent bond Polar covalent bond Atom 1 Atom 2 Ionic bondAtom 1Atom 2Difference in ENElectron sharinghigh ENvery littleequal or nearly equal sharinghigh ENmedium ENmoderateuneven sharinghigh ENlow ENlargetransfer of electronsEN = electronegativity
20Types of bondAn ionic crystalIonic bonds connect atoms to all neighbors, not just a single neighbor as in a molecule.
21Types of bond A metallic bond Like a covalent bond Like an ionic bondElectrons are sharedNo two atoms are specifically bonded togethermetallic bond: an attraction between metal atoms that loosely involve many electrons.
22Nonpolar covalent bond Polar covalent bond Ionic bondDifference in ENElectron sharingvery littleequal or nearly equal sharingmoderateuneven sharinglargetransfer of electronsEN = electronegativity
24Electronegativity of atoms: Difference in electronegativity:I – I = 2.66 – 2.66 = 0
25Electronegativity of atoms: I = 2.66 Difference in electronegativity:I – I = 2.66 – 2.66 = 0The I–I bond is nonpolar covalent.
26Difference in electronegativity: O – C = 3.44 – 2.55 = 0.89 of atoms:C = 2.55O = 3.44Difference in electronegativity:O – C = 3.44 – 2.55 = 0.89The C–O bond is polar covalent.0.89
27Nonpolar bonds in a molecule make the molecule nonpolar.
28Polar bonds in a molecule make the molecule polar.
29AssignmentWrite a three dollar summary of what you learned (a paragraph, with a topic sentence and three supporting sentences)Turn to page 224 and complete # 1 – 5 then turn them inHonors chemistry Homework:Page 224 #
34Ionic bondsWrite the electron configuration for a magnesium ion (Mg2+).Asked: Electron configuration of Mg2+Given: Mg, atomic number of 12, charge of +2Relationships: The electron configuration of magnesium is 1s22s22p63s2.
35Ionic formulasWhat is the correct formula for calcium oxide, a compound used in making paper and pottery, and adjusting the pH of soils?Asked: The formula for the ionic compound calcium oxideGiven: Calcium oxide is made from calcium and oxygen ions. Calcium forms +2 ions and oxygen forms –2 ions.Relationships: Ca2+ and O2– must combine in a ratio that will balance out the positive and negative charges.
36As stated earlier, elements share, lose or gain electrons to satisfy the octet rule and become more stableThe exception to the octet rule are those closest to helium such a hydrogen, lithium, beryllium and boron (since helium is the closest completely stable noble gasFor those elements mentioned above, the octet rule is more the duel rule or the rule of “2” these elements bond chemically to have a configuration of two electrons
37In a covalent bond, each shared electron is seen as a valence electron by both elements In H2, each atom shares a electron to have two electrons in their outer shellIn water H2O, each the hydrogen shares an electron with the oxygen giving them two valence electrons and oxygen eight valence electronsWhen ions are formed, they have an electron configuration of the closest noble gasNa+ has the neon configurationO2- has the Neon configuration
39Covalent bondsBonds form in such a way that each atom in the compound achieves the same number of valence electrons as the closest noble gas atom.
40Covalent bonds Ion formation Electrons are transferred so that each element has 8 valence electrons and has the same configuration as the closest noble gas. The light elements H, Li, Be, and B prefer to have 2 valence electrons.Ion formationAtoms gain or lose one or more electrons to reach the same electron configuration as the closest noble gas, with 8 valence electrons.octet rule: rule that states that elements transfer or share electrons in chemical bonds to reach a stable configuration of eight valence electrons.
41AssignmentOn the second section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.
42Ionic compounds generally form crystals because of the interchanging of +tive and –tive charges Ionic compounds are neutral even though they are made up of trillions of charged ionsThe formula of an ionic compound can be determined as long as you cancel the positive and negative
43As stated earlier, covalent bonds share electrons not transfer them The number of covalent bonds is equal to the number of unpaired valence electronsOnly hydrogen and nonmetals are commonly found as covalent bondsCarbon-like compounds form four covalent bondNitrogen-like compounds form three covalent bondOxygen-like compounds form two covalent bondHalogens form one covalent bond
44Carbon has four valence electrons and they are all unpaired Oxygen has six valence electrons, but only two are unpaired and able to form covalent bondsIf Lewis dot structures are drawn for elements, it can be used to tell the valence electrons and the unpaired electrons (which is the same as the number of possible covalent bonds)Atoms or molecules with unpaired electrons are highly reactive and are known as free radicalsFree radicals are responsible for aging, and diseases such as cancerAntioxidants are a good part of diet because they prevent free radicals form reacting with and damaging DNA
45AssignmentWrite a detailed three dollar summary of what you learned (a paragraph, with a topic sentence and three supporting sentences)Turn to page 224 and complete # 6 – 7,Page 226 # then turn them inHonors chemistry homeworkPage 225 #
46Vocabulary: Section 3 Isomer Free radical Antioxidant VSEPR Region of electron densityTrigonal planarLone pairsTetrahedralTrigonal pyramidalBent
47Why can’t a water molecule be like this? Each water molecule contains one oxygen atom and two hydrogen atoms.One central oxygen atomWhy can’t a water molecule be like this?One hydrogen atom on either side
48Why can’t a water molecule be like this? The oxygen forms one bondOne hydrogen forms two bondsOne hydrogen forms one bondThe Lewis structures indicate that it is not possibleWhy can’t a water molecule be like this?
49Lewis structures for individual atoms are like puzzle pieces. Put them together to form molecules.
50Use Lewis structures to predict: 1) the chemical formula2) the bonding pattern3) the shape of the moleculeTo be discussedlater in this sectionH2O is flat and bent
51Lewis Dot StructuresLewis dot structures allows chemist to be able to identify and predict how elements will join together to form moleculesIf you have a formula, you can use Lewis structures to determine how they will joinThe goal of using Lewis structures is to end up with each atom having no unpaired electrons and each having eight valence electrons (unless it is hydrogen, helium, lithium, beryllium or boron)
52The chemical formula for water is H2O Use Lewis structures to predict:1) the chemical formulaThe chemical formula for water is H2O(2 hydrogen atoms for every 1 oxygen atom)
53IsomersSometimes there is more than one way to satisfy the molecular formulaIsomers are when there is more than one way to represent a chemical formulaFor example, C2H6O can form ethanol as well as dimethyl ether (they both have different chemical and physical properties)
55Consider the chemical formula C2H6O Dimethyl ether
56Two isomers of C2H6OEthanolDimethyl etherisomer: a specific structure of a molecule, only used when a chemical formula could represent more than one molecule.
57Give three isomers for the formula C3H8O Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule.
58Give three isomers for the formula C3H8O Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule.Asked: The Lewis dot diagrams and structural formulas for the three molecules represented by the formula C3H8OGiven: Carbon has four unpaired electrons, hydrogen has one, and oxygen has two. Three carbons, eight hydrogens and one oxygen form each molecule.Relationships: The atoms will bond together such that all unpaired electrons will be paired up with electrons from other atoms.
59Give three isomers for the formula C3H8O Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule.Asked: The Lewis dot diagrams and structural formulas for the three molecules represented by the formula C3H8OGiven: Carbon has four unpaired electrons, hydrogen has one, and oxygen has two. Three carbons, eight hydrogens and one oxygen form each molecule.Relationships: The atoms will bond together such that all unpaired electrons will be paired up with electrons from other atoms.
60Double and Triple Bonds There are many compounds or molecules with more than one bond between two atomsEthene and ethyne have double and triple bonds respectivelyOxygen also has double bondsLewis dot structures show two dimensional representations of chemical bonding whit is a limitation since the 3D shape of a molecule determines the chemical properties of a moleculeVSEPR – Valence Shell Electron Pair RepulsionThe first three words “VSE” represent the valence electrons and how they react and the last two words “PR” represents the paired electrons that are not sharedPaired electrons are not shared in a chemical bond, but they do effect the shape of the moleculePaired electrons repel each other as well as repel shared ones
61Multiple bonds Sharing a pair of electrons is called a single bond. Carbon, nitrogen and oxygen commonly form double and triple bonds.Double bond(2 pairs of electrons)Triple bond(3 pairs of electrons)EtheneEthyne
62AssignmentOn the third section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.
63Electron DensityIf you rubbed a balloon against your hair, it would pull electrons off of your hair and become more negativeIf you put two charged balloons together, they would repel each other (since similar charges repel)The same thing happens when there are two regions of electron density around the atomThe electrons repel each other until they are the maximum distance apartWhen you have two balloons that are negatively charged, they move apart in a linear shape apart (180o)When they are three areas, the shape of the repulsion (120o) which is called trigonal planar shapedWhen they are four areas, the shape of the repulsion (109.5o) which is called tetrahedral shaped
64VSEPR theoryMolecular polarity is an uneven distribution of molecular charges between atomsVSEPR stands for valence-shell, electron-pair repulsionVSEPR theory states that repulsion between the sets of valence electrons surrounding an atom causes these sets
65Two areas of electron density repel to form linear shapes Two regionsTwo areas of electron density repel to form linear shapesThe two 180o angles formed around each carbon make the entire molecule straight.
66Three areas of electron density repel to form trigonal planar shapes Three regionsThree areas of electron density repel to form trigonal planar shapesThese three regions of electron density repel, forming 120o angles between the three atoms bonded to each carbon atom
67Four regionsThe four regions of electron density around the carbon repel, forming angles of 109.5o.
68Four regionsDifferent geometries formed by atoms with four regions of electron densityTetrahedralTrigonal pyramidalBent
69Water and ammonia have similar angles even though they are not the same.
71AssignmentWrite a detailed three dollar summary of what you learned (a paragraph, with a topic sentence and three supporting sentences)Turn to page 224 and complete # 8 – 14 then turn them inHonors chemistry homeworkPage 225 #
72Test: - Next week Tuesday or Thursday depending on your class. Homework requirement: Learn all terms and concepts covered on this topic.Make sure you have all assignments between page 224 and 227 completed and turned in by your test date.