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Chapter 6 – Chemical Bonds

Chapter 6 – Chemical Bonds. Jennie L. Borders. Standards. SPS1. Students will investigate our current understanding of the atom b. Compare and contrast ionic and covalent bonds in terms of electron movement.

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Chapter 6 – Chemical Bonds

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  1. Chapter 6 – Chemical Bonds Jennie L. Borders

  2. Standards • SPS1. Students will investigate our current understanding of the atom • b. Compare and contrast ionic and covalent bonds in terms of electron movement. • SPS2. Students will explore the nature of matter, its classification and its system for naming types of matter • B. Predict formulas for stable binary ionic compounds based on balance of charges • C. Use IUPAC nomenclature for transition between chemical names and chemical formulas of • Binary ionic compounds (containing representative elements) • Binary covalent compounds (ie. carbon dioxide, carbon tetrachloride

  3. Standards • SPS4. Students will investigate the arrangement of the periodic table. • a. Determine the trends of the following • Number of valence electrons • Types of ions formed by representative elements • Locations of metals, nonmetals and metalloids • Phases at room temperature

  4. Section 6.1 – Ionic Bonds • When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react. • The noble gases have stable electron configurations with eight valence electrons (or two in the case of helium).

  5. Stable Electron Configurations • The chemical properties of an element depend on the number of valence electrons. • An electron dot diagram is a model of an atom in which each dot represents a valence electron.

  6. Ionic Bonds • Some elements achieve stable electron configurations through the transfer of electrons between atoms. • An atom that has a net positive or negative charge is called an ion.

  7. Ions • An ion with a negative charge is an anion. Anions like the Cl- ion are named by adding the suffix –ide to the element name. (Ex. Cl- = chloride) • An ion with a positive charge is a cation. The name of a cation is the same as the element name. (Ex. Na+ = sodium)

  8. Ion Charges • The charges that an ion has are based on the number of valence electrons that an element has. • All of the elements in the same group have the same charge.

  9. Ion Charges • Is it easier for lithium to gain 7 more electrons or lose 1 electron? • What charge would lithium have? lose 1 electron +1

  10. Ion Charges • Is it easier for beryllium to gain 6 more electrons or lose 2 electrons? • What charge would beryllium have? lose 2 electrons +2

  11. Ion Charges • Is it easier for boron to gain 5 more electrons or lose 3 electrons? • What charge would boron have? lose 3 electrons +3

  12. Ion Charges • Is it easier for carbon to gain 4 more electrons or lose 4 electrons? • What charge would carbon have? lose or gain 4 electrons +4 or -4

  13. Ion Charges • Is it easier for nitrogen to gain 3 more electrons or lose 5 electrons? • What charge would nitrogen have? gain 3 electrons -3

  14. Ion Charges • Is it easier for oxygen to gain 2 more electrons or lose 6 electrons? • What charge would oxygen have? gain 2 electrons -2

  15. Ion Charges • Is it easier for fluorine to gain 1 more electron or lose 7 electrons? • What charge would fluorine have? gain 1 electron -1

  16. Ion Charges • Would neon want to gain or lose electrons? • What charge would neon have? No, it has a full energy level 0

  17. Ion Charges • Since elements in the same group have the same number of valence electrons, they all have the same charge.

  18. Formation of Ionic Bonds • A chemical bond is the force that holds atoms or ions together as a unit. • An ionic bond is the force that holds cations and anions together. • An ionic bond forms when electrons are transferred from one atom to another.

  19. Formation of Ionic Bonds • When an ionic bond is formed, electrons are transferred until each atom has a full outer energy level.

  20. Ionic Compounds • Compounds that contain ionic bonds are ionic compounds, which can be represented by chemical formulas. • A chemical formula is a notation that shows what elements a compound contains and the ratio of the atoms or ions of these elements in the compound.

  21. Crystal Lattices • A chemical formula for an ionic compound tells you the ratio of the ions in the compound. • Solids whose particles are arranged in a lattice structure are called crystals.

  22. Properties of Ionic Compounds • Ionic compounds tend to have high melting points (above 300oC). • Ionic compounds are poor conductors in the solid state, but they can conduct heat or electricity when they are melted. • Ionic compounds are brittle, so they shatter when struck by a hammer. • The properties of ionic compounds can be explained by the strong attractions among ions within a crystal lattice.

  23. Ionic Compounds and Electricity

  24. Section 6.1 Assessment • When is an atom least likely to react? • Describe one way an element can achieve a stable electron configuration. • What characteristic of ionic bonds can be used to explain the properties of ionic compounds? • What will the ratio of ions be in any compound formed from a Group 1 metal and a Group 7 nonmetal?

  25. Section 6.1 Assessment • Why do ionic compounds include at least one metal? • Based on their chemical formulas, which of these compounds is not likely to be an ionic compounds: KBr, SO2, or FeCl3?

  26. Section 6.2 – Covalent Bonding • A covalent bond is a chemical bond in which two atoms share a pair of valence electrons. • When two atoms share one pair of electrons, the bond is called a single bond.

  27. Covalent vs Ionic Bond

  28. Molecules of Elements • A molecule is a neutral group of atoms that are joined together by one or more covalent bonds. • The attractions between the shared electrons and the protons in each nucleus hold the atoms together in a covalent bond. • Many nonmetal elements exist as diatomic molecules. Diatomic means two atoms. They are H2, F2, Cl2, N2,Br2, O2, and I2.

  29. Diatomic Elements

  30. Multiple Covalent Bonds • When two atoms share two pairs of electrons, the bond is called a double bond. • When two atoms share three pairs of electrons, the bond is called a triple bond.

  31. Section 6.2 Assessment • What attractions hold atoms together in a covalent bond? • Which of these elements does not bond to form molecules: oxygen, chlorine, neon, or sulfur? • Based on their electron dot diagrams, what is the formula for the covalently bonded compound of nitrogen and hydrogen?

  32. Section 6.3 – Naming Compounds and Writing Formulas • The name of an ionic compound must distinguish the compound from other ionic compounds containing the same elements. • The formula of an ionic compound describes the ratio of the ions in the compound.

  33. Binary Ionic Compounds • A compound made from only two elements is a binary compound. • When naming an ionic compound the name of the metal (cation) does not change and the name of the nonmetal (anion) has the suffix –ide. • Ex. MgBr2 = magnesium bromide

  34. Metal with Multiple Ions • Many transition metals form more than one type of ion. • When a metal forms more than one ion, the name of the ion contains a roman numeral to indicate the charge of the ion. • Ex: Fe+2 = iron (II) Fe+3 = iron (III)

  35. Polyatomic Ions • A covalently bonded group of atoms that has a positive or negative charge and acts as a unit is a polyatomic ion.

  36. WRITING FORMULAS FOR IONIC COMPOUNDS • Place the symbol of the cation first, followed by the symbol of the anion. • Use subscripts to show the ratio of the ions in the compound. • Because all compounds are neutral, the total charges on the cations and anions must add up to zero.

  37. Crossing Charges • To balance the charges in an ionic compound, you can cross the charges if they are not the same.

  38. Describing Molecular Compounds • The name and formula of a molecular compound describe the type and number of atoms in a molecule of the compound. • Molecular compounds only contain nonmetals.

  39. Naming Molecular Compounds • The name of the first element is the same. The name of the second element ends in the suffix -ide. • Prefixes tell the number of atoms of each element. A prefix is not used when the first element only has 1 atom. • Ex. CO2 = carbon dioxide

  40. Prefixes 1 = mono 6 = hexa 2 = di 7 = hepta 3 = tri 8 = octa 4 = tetra 9 = nona 5 = penta 10 = deca

  41. Writing Molecular Formulas • Write the symbols for the elements in the order the elements appear in the name. The prefixes indicate the number of atoms of each element in this molecule. • Ex: diphosphorus pentoxide = P2O5

  42. Section 6.3 Assessment • What does the formula of an ionic compound describe? • What do the name and formula of a molecular compound describe? • What suffix is used to indicate an anion? • Why are Roman numerals used in the names of compounds that contain transition metals? • What is a polyatomic ion?

  43. Section 6.3 Assessment • How is it possible for two different ionic compounds to contain the same elements? • How many potassium ions are needed to bond with a phosphate ion? • What are the name of these ionic compounds: LiCl, BaO, and Na3N? • Name the molecular compounds with these formulas: N2O7 and CO. • What is the formula for the ionic compound formed from potassium and sulfur?

  44. Section 6.4 – The Structure of Metals • In a metal, valence electrons are free to move among the atoms, so the cations are surrounded by a sea of electrons. • A metallic bond is the attraction between a metal cation and the shared electrons that surround it.

  45. Metallic Bonds • The cations in a metal form a lattice that is held in place by strong metallic bonds between the cations and the surrounding valence electrons. • The more valence electrons an atom can contribute to the shared pool, the stronger the metallic bond will be.

  46. Properties of Metals • The mobility of electrons within a metal lattice explains the fact that metals are good conductors and malleable.

  47. Alloys • An alloy is a mixture of two or more elements that have metallic properties.

  48. SECTION 6.4 ASSESSMENT • What holds metal ions together in a metal lattice? • What characteristic of a metallic bond explains some of the properties of metals? • Explain why the metallic bonds in some metals are stronger than the bonds in other metals. • Why are metals good conductors of electric current? • Can two different elements form a metallic bond together?

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