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UNIT 2: Structure and Properties of Matter Chapter 3: Atomic Models and Properties of Atoms Chapter 4: Chemical Bonding and Properties of Matter.

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Presentation on theme: "UNIT 2: Structure and Properties of Matter Chapter 3: Atomic Models and Properties of Atoms Chapter 4: Chemical Bonding and Properties of Matter."— Presentation transcript:

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2 UNIT 2: Structure and Properties of Matter Chapter 3: Atomic Models and Properties of Atoms Chapter 4: Chemical Bonding and Properties of Matter

3 Chapter 4: Chemical Bonding and Properties of Matter UNIT 2 The chemical bonding in a substance influences the shape of its molecules, and molecular shape influences the properties of that substance. One of the properties of iron is its strength, which makes it ideal for use in support structures. TO PREVIOUS SLIDEPREVIOUS The strength of iron makes it useful in items such as horseshoes. Chapter 4: Chemical Bonding and Properties of Matter

4 UNIT 2 Section Models of Chemical Bonding Chapter 4: Chemical Bonding and Properties of Matter TO PREVIOUS SLIDEPREVIOUS Three types of chemical bonding are ionic, covalent, and metallic.

5 UNIT 2 Section 4.1 Electronegativity TO PREVIOUS SLIDEPREVIOUS Electronegativity is the relative ability of an atom to attract shared electrons in a chemical bond. What general trends in electronegativity are shown in the periodic table? Chapter 4: Chemical Bonding and Properties of Matter

6 UNIT 2 Section 4.1 Electron Sharing and Electronegativity Electronegativity difference, ΔEN, between two atoms bonded together can be low, intermediate, or high. The electron density diagrams below show the differences in the bonds. when ΔEN is 0: electrons are equally shared when ΔEN is 1: electrons are more closely associated with the more electronegative atom when ΔEN is high, there is little sharing of electrons TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Bonding is a continuum between equal sharing and minimal sharing of electrons.

7 UNIT 2 Section 4.1 Scientists have categorized types of bonds according to ΔEN. ΔEN between 1.7 and 3.3: mostly ionic ΔEN between 0.4 and 1.7: polar covalent ΔEN between 0.0 and 0.4: mostly covalent (non-polar) Three categories of bonds have been set based on ΔEN. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Electron Sharing and Electronegativity

8 Chemists use the electron-sea model to describe metallic bonding. The model proposes that the valence electrons of metal atoms move freely among the ions, forming a “sea” of delocalized electrons that hold the metal ions rigidly in place. UNIT 2 Section 4.1 Metallic Bonding TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Microscopic analysis shows that the structure of metals consists of aggregates of crystals.

9 UNIT 2 Section 4.1 Properties of Metals Melting and Boiling Points the stronger the bonding forces, the higher the melting and boiling points of pure metals TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Periodic table trends include: 1. For Group 1, melting points decrease as the atomic number increases. 2. For Groups 1 to 6, across a period, melting points increase as atomic number increases.

10 UNIT 2 Section 4.1 Properties of Metals TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Malleability and Ductility Based on the electron-sea model, metals can be shaped because, when struck, the metal ions can slide by one another while the electrons still surround them. Hardness The variation between metals is due to differences in crystal size (smaller ones make harder metals). Electrical and Thermal Conductivity Metals are good conductors because their electrons are free to move from one atom to the next.

11 UNIT 2 Section 4.1 Alloys Alloys are solid mixtures of two or more metals. the addition of the second metal, even in a very small amount, can significantly affect the properties of a substance in some cases, non-metal atoms, such as carbon, are added TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter If atoms of the second metal are similar in size to the first metal, they take the place of those atoms. If atoms of the second metal are much smaller than atoms of the first metal, they will fit in spaces between the larger atoms.

12 occurs when ΔEN is between 1.7 and 3.3 essentially, involves one atom losing one or more electrons and another atom gaining those electron(s) UNIT 2 Section 4.1 Ionic Bonding There are different ways to show the transfer of electrons in the formation of ionic compounds. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

13 Ionic compounds exist as crystal lattice structures with particular patterns of alternating positive and negative ions. The unit cell is the smallest group of ions that is repeated. UNIT 2 Section 4.1 Ionic Crystals NaCl forms a cubic crystal lattice structure. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Different types of crystal structures can form. the relative sizes and charges of the ions affect the type of crystal structure that an ionic compound will form.

14 UNIT 2 Section 4.1 Properties of Ionic Compounds Melting and Boiling Points high due to very strong attractions between ions TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Solubility ionic compounds are soluble in water when the attractive forces between the ions and water molecules are stronger than the attractive forces among the ions themselves When sodium chloride (NaCl) dissolves in water, attractive forces between water molecules and NaCl ions act to break apart the ionic bonds.

15 UNIT 2 Section 4.1 Properties of Ionic Compounds TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Conductivity solids do not conduct because ions cannot move compounds conduct when dissolved in water and ions can move Mechanical Properties hard and brittle, so will break apart when struck Ionic crystal will break on smooth planes, where like charges become aligned.

16 UNIT 2 Section 4.1 Covalent Bonding The length of a covalent bond is determined by different electrostatic forces. Forces in covalent bonds: both attractive and repulsive forces play a role TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter occurs when ΔEN is less than 1.7 covalent bonds are classified into two types: polar covalent: atoms do not share electrons equally non-polar covalent: atoms share electrons almost equally

17 Describe the chemical bonding and structure of NaCl. How do bonding and structure influence the general properties of the substance? UNIT 2 Section 4.1 Answer on the next slide TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter L EARNING C HECK

18 NaCl is composed of a metal atom bonded to a non-metal atom with ΔEN > 1.7. As such, the bond is classified as ionic. It exists as a cubic crystal lattice structure, with an alternating pattern of chloride ions and sodium ions. Properties of NaCl include high melting and boiling points; solubility in water; hard and brittle; a poor conductor as a solid, but it does conduct electricity when dissolved in water. Section 4.1 UNIT 2 TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter L EARNING C HECK

19 UNIT 2 Section 4.1 Quantum Mechanics and Bonding Valence Bond (VB) Theory explains bond formation and molecular shapes based on orbital overlap. The region of overlap has a maximum capacity of two electrons, which have opposite spins. There should be maximum overlap of orbitals, since the greater the overlap, the stronger and more stable the bond. Atomic orbital hybridization is used to help explain the shapes of some molecules. Quantum mechanics is used to explain and describe chemical bonding. It is also used to account for shapes of molecules. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

20 UNIT 2 Section 4.1 Quantum Mechanics and Bonding According to MO theory: Covalent bond formation involves atomic orbital overlap that results in formation of new orbitals called molecular orbitals. Molecular orbitals have shapes and energy levels that are different from those of atomic orbitals. The electrons in molecular orbitals are delocalized throughout the orbital. Molecular Orbital (MO) Theory explains bond formation and molecular shapes based on the formation of new molecular orbitals. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

21 UNIT 2 Section 4.1 Explaining Single Bonds For molecules like hydrogen fluoride: the 1s orbital of H overlaps with the half-filled 2p orbital of F TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter According to MO theory, the bond is a sigma (σ) bond, which is symmetrical and freely rotates.

22 UNIT 2 Section 4.1 Explaining Single Bonds TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter For molecules like methane: the VB theory of hybrid orbitals is used to explain molecular shape carbon forms four hybrid orbitals (sp 3 ) by combining three 2p orbitals and a 2s orbital so that four identical bonds can be created The four sp 3 orbitals of C overlap with the s orbitals of H to form methane.

23 UNIT 2 Section 4.1 Explaining Double Bonds TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Hybrid orbitals are used to explain the structure of ethene or molecules like ethene. it is planar with ~120º bond angles the structure is explained by formation of 3 sp 2 hybrid orbitals for each carbon (a 2s orbital mixes with two 2p orbitals)

24 UNIT 2 Section 4.1 Explaining Double Bonds TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter For bond formation in ethene: one sp 2 orbital of each carbon overlaps to form a σ bond between the carbons two sp 2 orbitals of each carbon overlap with the 1s orbitals of the hydrogens to form σ bonds the lobes of the 2p orbitals of each carbon overlap above and below the plane to form a pi (π) bond

25 UNIT 2 Section 4.1 Explaining Triple Bonds TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter For molecules like ethyne: the linear structure is explained by formation of 2 sp hybrid orbitals for each carbon (a 2s orbital + a 2p orbital) sigma bonds form from overlap between sp of each carbon and between sp of carbons and 1s of hydrogens two pi bonds form from overlap of the two 2p orbitals of each carbon

26 UNIT 2 Section 4.1 Types of Hybridization TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter The names of hybrid orbitals (formed by the combination of two or more orbitals in the valance shell of an atom) indicate the number and types of atomic orbitals that were combined. Atoms of Period 3 elements can have d orbital hybridization with s and p orbitals. The number of hybrid orbitals that form is the same as the number of atomic orbitals that are combined. Each hybrid orbital has a certain overall shape.

27 Allotropes are compounds that consist of the same element but have different physical properties. UNIT 2 Section 4.1 Allotropes Allotropes of carbon: A graphite, B diamond, C buckyballs, D nanotubes An example is allotropes of carbon, which differ in the pattern of covalent bonds between carbon atoms. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

28 Network solids are substances that consist of atoms bonded covalently in a continuous two- or three-dimensional array. There is no natural beginning or end to the chains of atoms. UNIT 2 Section 4.1 Covalent Network Solids Silicon dioxide, SiO 2, exists as a network solid that is represented as (SiO 2 ) n. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

29 Section 4.1 Review UNIT 2 Section 4.1 TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

30 UNIT 2 Section Shapes, Intermolecular Forces, and Properties of Molecules TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Molecular compounds form a much greater variety of structures than ionic compounds form. Understanding the properties of molecules requires an understanding of their three-dimensional shapes. Different theories and models are used to predict molecular shapes. The shape of a molecule is the result of the presence of atoms, bonding electrons, and non-bonding electrons, as well as forces of attraction and repulsion.

31 UNIT 2 Section 4.2 Depicting Two-Dimensional Structures of Molecules with Lewis Structures TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

32 UNIT 2 Section 4.2 Some Exceptions When Drawing Lewis Structures The ammonium ion has a co-ordinate covalent bond. Co-ordinate Covalent Bonds: one atom contributes both electrons bonds behave the same way as other covalent bonds and therefore are not indicated in Lewis structures TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Expanded Octet (Expanded Valence): central atom has more than an octet of electrons a feature of some Period 3 and higher elements For SF 6 (g), 12 electrons are around the central atom.

33 UNIT 2 Section 4.2 Some Exceptions When Drawing Lewis Structures In BF3(g), boron has an incomplete octet. An Incomplete Octet: central atom has fewer than an octet of electrons TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Resonance Structures: measured bond lengths may not support Lewis structures one of two or more Lewis structures that show same relative position of atoms but different positions of electron pairs Actual bond lengths in ozone are between those of single and double bonds.

34 UNIT 2 Section 4.2 Predicting the Shapes of Molecules Using VSEPR Theory The valence-shell electron pair repulsion (VSEPR) theory TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter For VSEPR, there are five electron-group arrangements. (Electron groups are represented by bars). is a model used to predict molecular shape is based on electron groups around a central atom being positioned as far apart as possible (repulsion) predicts certain arrangements of electron groups

35 UNIT 2 Section 4.2 Electron Groups and Molecular Shapes TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

36 UNIT 2 Section 4.2 Electron Groups and Molecular Shapes If one or more electron groups around a central atom is a lone pair, different strengths of repulsive forces will alter bond angles to differing degrees. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

37 UNIT 2 Section 4.2 Summarizing Molecular Shapes TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

38 UNIT 2 Section 4.2 Summarizing Molecular Shapes TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

39 UNIT 2 Section 4.2 Guidelines for Using VSEPR Theory to Predict Molecular Shape TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

40 What is the electron-group arrangement and molecular shape of HCN? UNIT 2 Section 3.2 Answer on the next slide TO PREVIOUS SLIDEPREVIOUS Chapter 3: Atomic Models and Properties of Atoms L EARNING C HECK

41 HCN has two bonding groups and no lone pairs. The electron-group arrangement is linear, and the shape of the molecule is also linear. Section 3.2 UNIT 2 TO PREVIOUS SLIDEPREVIOUS Chapter 3: Atomic Models and Properties of Atoms L EARNING C HECK

42 UNIT 2 Section 4.2 Determining the Hybridization of the Central Atom of a Molecule or Ion Chapter 4: Chemical Bonding and Properties of Matter TO PREVIOUS SLIDEPREVIOUS

43 What is the hybridization for the phosphorus atom in the molecule below? UNIT 2 Section 4.2 Answer on the next slide TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter L EARNING C HECK

44 The electron-group arrangement for phosphorus is tetrahedral. Therefore, P has an sp 3 hybridization. Section 4.2 UNIT 2 TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter L EARNING C HECK

45 UNIT 2 Section 4.2 The Influence of Molecular Shape on Polarity The shape of a molecule affects that molecule’s polarity. polar bonds have a bond dipole bond dipoles are indicated using vectors that point in the direction of higher electron density TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter In a polar covalent bond, a partial positive charge is associated with one atom and a partial negative charge is associated with the other atom.

46 UNIT 2 Section 4.2 Determining Whether a Molecule is Polar A molecule with one or more polar bonds is not necessarily a polar molecule. The molecule’s shape must be considered. The polarity as a whole can be determined by adding the vectors. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Both water and carbon dioxide have two polar bonds. But water’s bent shape results in a polar molecule, while carbon dioxide’s linear shape results in a non-polar molecule.

47 UNIT 2 Section 4.2 Molecular Shapes and Polarities TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter

48 UNIT 2 Section 4.2 How Intermolecular Forces Affect the Properties of Solids and Liquids Intermolecular forces exist between ions and molecules and influence the physical properties of substances. TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Categories of forces: dipole-dipole ion-dipole induced dipole dispersion

49 UNIT 2 Section 4.2 Dipole-Dipole Dipole-dipole forces: are forces of attraction between polar molecules, which have a region of partial positive charge and a region of partial negative charge are a main reason for melting and boiling point differences between polar and non-polar molecules include hydrogen bonding, as an example of one type TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Hydrogen bonding (dotted lines) in water

50 UNIT 2 Section 4.2 Ion-Dipole TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter Ion-dipole intermolecular forces. Ion-dipole forces: are forces of attraction between partial charges on polar molecules and ions depend on the size and charge of the ion and the magnitude of the partial charge and size of the molecule are involved in the process of hydration

51 UNIT 2 Section 4.2 Induced Dipoles TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter A dipole can be induced in a non-polar molecule. Dipole-induced dipole forces: are forces of attraction between a polar molecule and a non-polar molecule that has an induced (temporary) dipole due to the nearby polar molecule Ion-induced dipole forces: are forces of attraction between an ion and a non-polar molecule that has an induced dipole due to the nearby ion

52 UNIT 2 Section 4.2 Dispersion Forces TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter The more linear molecule has a higher boiling point because the dispersion forces are greater. Dispersion forces: are forces of attraction between all molecules, including non-polar molecules are due to spontaneous temporary dipoles that form due to the constant motion of electrons in covalent bonds depend on the size and shape of the molecules the larger and more linear the molecule, the greater the force of attraction

53 Section 4.2 Review UNIT 2 Section 4.2 TO PREVIOUS SLIDEPREVIOUS Chapter 4: Chemical Bonding and Properties of Matter


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