CHEMICAL BONDS CHAPTER 7,8

CHAPTER 7 CHEMICAL BONDS 6.1 IONIC BONDING 6.2 COVALENT BONDING 6.3 NAMING COMPOUNDS & WRITING FORMULAS 6.4 THE STRUCTURE OF METALS

Objectives Identify when an atom is unlikely to react Ionic Bonding Identify when an atom is unlikely to react Identify one way in which elements can achieve stable electron configurations Determine how the structure of an ionic compound affect its properties

CHAPTER 7 CHEMICAL BONDS Ionic Bonding Bonding Why are Noble Gases inert (nonreactive)? Stable electron configuration – the highest occupied energy level of the noble gas atom is filled. Eight valence electrons in the case of all Noble gases Except Helium(He), which has two…however is still filled Other elements tend to react to achieve the same stable electron configuration as the Noble Gases… filled outermost energy levels.

CHAPTER 7 CHEMICAL BONDS Ionic Bonding Electron Dot Diagrams An electron dot diagram is a model of an atom in which each dot represents a valence electron, and the element symbol represents the nucleus and all other electrons of the atom. Examples:

CHAPTER 7 CHEMICAL BONDS Ionic Bonding Ionic Bonds – Transfer of Electrons Atoms of elements that do not have a complete set of valence electrons tend to react with other atoms to form stable electron configurations. Some elements do this by a transfer of electrons: Ionic bonding. When an atom gains or loses electrons, the number of protons and electrons is no longer equal. It now has a net positive or negative charge and is an ion. An ion is a charged atom.

CHAPTER 6 CHEMICAL BONDS Ionic Bonding Ionic Bonds – Formation of Ions Cations = Positve Charge If an ion has more protons than electrons, it has a net positive charge, and is called a cation. Represented by a superscript plus sign to the right of the element symbol. Example : Na+ Named after their elements. For example, Na+ is called the sodium ion. Anions = Negative Charge If an ion has more electrons than protons, it has a net negative charge, and is called a anion. Represented by a superscript minus sign to the right of the element symbol. Example : Cl- Named by using part of the element name plus the suffix -ide. For example, Cl- is called the chloride ion.

CHAPTER 6 CHEMICAL BONDS Ionic Bonding

CHAPTER 6 CHEMICAL BONDS Ionic Bonding Formation of Ionic Bonds OPPOSITES ATTRACT: Once ions are formed from the transfer of electrons, the positive and negative ions are attracted to each other and form chemical bond. A chemical bond is the force that holds atoms or ions together as a unit. An ionic bond is the force that holds anions and cations together.

CHAPTER 6 CHEMICAL BONDS Ionic Bonding

CHAPTER 7 CHEMICAL BONDS Ionic Bonding Ionization Energy For an atom to lose an electron, the electron must gain enough energy to overcome its attraction to the positive nucleus. The amount of energy required to remove an electron is called ionization energy. It varies from element to element. The lower the ionization energy (IE), the easier it is to remove an electron from an atom.

CHAPTER 7 CHEMICAL BONDS Ionic Bonding Ionization Energies of the A Group Elements Which group has the highest ionization energies? Why? Which group has the lowest ionization energies? Why? Which element has the lowest ionization energy? Why? Which element has the highest ionization energy? Why?

CHAPTER 7 CHEMICAL BONDS Ionic Bonding Ionic Compounds Ionic compounds (contain ionic bonds) can be represented by chemical formulas Chemical Formula: Shows elements in a compound with element symbols Gives ratios of atoms or ions in the compound via subscripts If only one atom of an element is present, no subscript is required Examples: NaCl MgCl2

CHAPTER 7 CHEMICAL BONDS Ionic Bonding Properties of Ionic Compounds Tend to form crystal lattices (repeating patterns of ions resulting from attractions between positive and negative ions.) Properties of ionic compounds can be explained by strong attractions among ions in a crystal lattice. High melting point (a lot of energy required to break attractions between ions.) Solid state is brittle (pushing like ions together causes them to repel in a “rebound effect”) Solid has poor conductivity (ions can’t move), but liquid state has high conductivity (ions can move)

CHAPTER 7 CHEMICAL BONDS Ionic Bonding Bonding Basics Worksheet Write the electron dot diagram (Lewis Structure) for each element. Use one color for the electrons in metals, and another color for the electrons in nonmetals. Draw an arrow (or more if needed) with a different color to show the transfer of electrons, and move the colored dot to the new location. Determine the charge for each ion and write the formula. Make sure the sum of the oxidation numbers is zero and write the chemical formula.

Objectives Covalent Bonding Determine how atoms are held together in a covalent bond Identify what happens when atoms don’t share electrons equally List the factors that determine whether a molecule is polar Compare and contrast the attractions between polar and nonpolar molecules

CHAPTER 8 CHEMICAL BONDS Covalent Bonding Covalent Bonds Covalent Bonds (Co- means “to share” / -valent refers to valence electrons) Chemical bond in which two atoms share a pair of valence electrons Attractions between shared electrons and the protons in each nucleus hold the atoms together Molecule: a neutral group of atoms joined by one or more covalent bonds Multiple covalent bonds: sometimes 2 atoms can share more than one pair of electrons 2 shared pairs: double bond (4 electrons total are shared ) 3 shared pairs : triple bond (6 electrons are shared) O O O2

CHAPTER 8 CHEMICAL BONDS Covalent Bonding Covalent Bonds Representation (example: hydrogen gas, or H2) Electron Dot diagram Structural Formula (dash represents a pair of shared electrons) For Multiple bonds, multiple lines between two atoms would be used. ELECTRON DOT DIAGRAM H H

CHAPTER 8 CHEMICAL BONDS Covalent Bonding Covalent Bonds Representation (example: hydrogen gas, or H2) Electron Dot diagram Structural Formula (dash represents a pair of shared electrons) For Multiple bonds, multiple lines between two atoms would be used. ELECTRON DOT DIAGRAM H H

CHAPTER 8 CHEMICAL BONDS Covalent Bonding Covalent Bonds Representation (example: hydrogen gas, or H2) Electron Dot diagram Structural Formula (dash represents a pair of shared electrons) For Multiple bonds, multiple lines between two atoms would be used. ELECTRON DOT DIAGRAM H H Shared Electrons

CHAPTER 8 CHEMICAL BONDS Covalent Bonding Polar vs Nonpolar Bonds Unequal sharing of electrons Some atoms have a greater attraction for electrons Electronegativity: the ability of an atom to attract electrons to itself in a covalent bond. Polar Covalent Bond Electrons shared UNEQUALLY between 2 atoms The two atoms have DIFFERENT electronegativities Nonpolar Covalent Bond Electrons shared EQUALLY between 2 atoms The two atoms have SIMLAR electronegativities.

CHAPTER 8 CHEMICAL BONDS Covalent Bonding Polar Molecules Polar molecules have partial positive and negative charges at opposite ends (like a magnet has North and South poles) Partial negative charge: δ- Partial positive charge:δ+ Polarity of a molecule is determined by Type of covalent bonds (polar or nonpolar) Shape of molecule Polar molecule Nonpolar molecule

CHAPTER 8 CHEMICAL BONDS Covalent Bonding Attraction Between Molecules All molecules have a force of attraction between them. Attractions between polar molecules like water, are stronger than those between nonpolar molecules In water, these attractions are called hydrogen bonds (partial positive hydrogen ends attract partial negative oxygen ends) This explains many of water strange and important properties: High surface tension High adhesion and cohesion Lower density in solid state (ice floats!)

Objectives Naming Compounds & Writing Formulas List the information that the name and formula of an ionic compound provide Determine what information does the name and formula of a molecular compound provide

CHAPTER 7 CHEMICAL BONDS Naming Compounds & Writing Formulas Naming Ionic Compounds A compound made from only two elements is a binary ionic compound. Naming ionic compounds is easy: It’s the name of the cation (positive ion) Followed by the name of anion (negative ion), it has the suffix –ide. Let’s take calcium and iodine as an example: Calcium is the name of the cation and, iodide is the name of the anion, therefore: calcium iodide

CHAPTER 7 CHEMICAL BONDS Naming Compounds & Writing Formulas Writing Ionic Compounds Once again let’s look at calcium iodide: What are their oxidation numbers? Cross them (only the numbers…no charges!) Don’t write ones! Rewrite the formula +2 -1 Ca I CaI2

CHAPTER 7 CHEMICAL BONDS Naming Compounds & Writing Formulas Describing Ionic Compounds The following are two substances, both made with compounds of copper and oxygen. The name of an ionic compound must distinguish the compound from other ionic compounds containing the same elements. Copper (I) oxide – Cu2O Copper (II) oxide – CuO

CHAPTER 7 CHEMICAL BONDS Naming Compounds & Writing Formulas Metals with Multiple Ions Remember an Ion is: a charged atom 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 on the ion.

CHAPTER 7 CHEMICAL BONDS Naming Compounds & Writing Formulas Copper and Oxygen Copper (I) oxide Copper (II) oxide +1 -2 +2 -2 Cu O Cu O Cu2O Cu2O2 CuO

CHAPTER 7 CHEMICAL BONDS Naming Compounds & Writing Formulas Polyatomic Ions A polyatomic ion is a covalently bonded group of atoms that has a positive or negative charge, and acts as a single unit (like an ion). The prefix poly- means many Most polyatomic ions are anions, which means they will have a negative charge. Sometimes parentheses are used in a formula to denote the number of polyatomic ions are included within that formula.

CHAPTER 7 CHEMICAL BONDS Naming Compounds & Writing Formulas Naming & Writing Compounds with Polyatomic Ions Let’s look at calcium and phosphate (a polyatomic ion) NOTHING CHANGES!, follow the same steps as before! What are their oxidation numbers? Cross them. (Only the numbers, NO CHARGES) Don’t write ones! Rewrite the formula. Use parentheses if necessary The name of this compound is: calcium phosphate +2 -3 Ca PO4 Ca3(PO4)2 Ca3PO42

CHAPTER 7 CHEMICAL BONDS Naming Compounds & Writing Formulas Math Practice Write the formula for the compound calcium oxide. Write the formula for the compound copper(I) sulfide. Write the formula for the compound sodium sulfate. Write is the name of the compound whose formula is NaOH? CaO Cu2S Na2SO4 sodium hydroxide

CHAPTER 8 CHEMICAL BONDS Naming Compounds & Writing Formulas Describing Molecular Compounds Molecular compounds are those compounds formed by sharing electrons, covalently bonded. The name and formula of a molecular compound describe the type and number of atoms in a molecule of the compound. The general rule is the most metallic element appears first in the name. If both elements are in the same group, the more metallic element is closer to the bottom of the group. The name of the second element is changed to end in the suffix –ide. (as in carbon dioxide)

CHAPTER 8 CHEMICAL BONDS Naming Compounds & Writing Formulas Naming Molecular Compounds Number of Atoms Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca- When naming molecular compounds prefixes are used to denote the number of atoms of each element within the molecule. The prefix mono- is often is not used for the first element in the name. N2O4 dinitrogen tetroxide

CHAPTER 8 CHEMICAL BONDS Naming Compounds & Writing Formulas Naming Molecular Compounds Number of Atoms Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca- P2O5 diphosphorus pentoxide CO carbon monoxide

CHAPTER 8 CHEMICAL BONDS Naming Compounds & Writing Formulas Writing Molecular Compounds Number of Atoms Prefix 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca- carbon tetrafluoride CF4 pentaphosphorus decoxide P5O10

CHAPTER 8 CHEMICAL BONDS The Structure of Metals What are the forces that give a metal its structure as a solid? How do metallic bonds produce some of the typical properties of metals? How are the properties of alloys controlled?