CHAPTER 7,8. 6.1 IONIC BONDING 6.2 COVALENT BONDING 6.3 NAMING COMPOUNDS & WRITING FORMULAS 6.4 THE STRUCTURE OF METALS

CHEMICAL BONDSCHAPTER 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

Identify one way in which elements can achieve stable electron configurations

Determine how the structure of an ionic compound affect its properties

Ionic Bonding

BondingWhy 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 gasesExcept 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.

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CHEMICAL BONDS Ionic Bonding

Electron Dot DiagramsAn 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:

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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.

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Ionic Bonds – Formation of Ions

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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


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 holdsatoms or ions together as a unit.

An ionic bond is the force that holds anionsand cations together.

CHAPTER 6


CHAPTER 6


Ionization EnergyFor 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.

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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?

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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

requiredExamples: NaCl MgCl2

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Properties of Ionic CompoundsTend 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)

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Bonding Basics Worksheet

1. Write the electron dot diagram (Lewis Structure) for each element.

2. Use one color for the electrons in metals, and another color for the electrons in nonmetals.

3. 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.

4. Determine the charge for each ion and write the formula.

5. Make sure the sum of the oxidation numbers is zero and write the chemical formula.

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

Objectives 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)

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CHEMICAL BONDS Covalent Bonding

O O O2

Covalent BondsRepresentation (example: hydrogen gas, or H2)

Electron Dot diagramStructural Formula (dash represents a pair of shared electrons)For Multiple bonds, multiple lines between two atoms would be used.

ELECTRON DOT DIAGRAM

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H H




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H H




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H H Shared Electrons

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.

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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

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Polar molecule Nonpolar molecule

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!)

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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

Objectives Naming Compounds & Writing Formulas

Naming Ionic CompoundsA 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:

CHAPTER 7

CHEMICAL BONDSNaming Compounds & Writing Formulas

Calcium is the name of the cation and, iodide is the name of the anion, therefore: calcium iodide

Writing Ionic CompoundsOnce 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

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Ca I +2 -1

CaI2

Describing Ionic CompoundsThe 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.

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Copper (I) oxide – Cu2O Copper (II) oxide – CuO

Metals with Multiple IonsRemember an Ion is: a charged atomMany 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.

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Copper and Oxygen

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Copper (I) oxide Copper (II) oxide

Cu O Cu O+1 -2 +2 -2

Cu2O Cu2O2 CuO

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.

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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

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Ca PO4

+2 -3

Ca3PO42Ca3(PO4)2

Math Practice

1. Write the formula for the compound calcium oxide.

2. Write the formula for the compound copper(I) sulfide.

3. Write the formula for the compound sodium sulfate.

4. Write is the name of the compound whose formula is NaOH?

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CaO

sodium hydroxide

Na2SO4

Cu2S

Describing Molecular CompoundsMolecular 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)

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CHAPTER 8


Number of Atoms Prefix

1 mono-2 di-3 tri-4 tetra-5 penta-6 hexa-7 hepta-8 octa-9 nona-

10 deca-

Naming Molecular Compounds• 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

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10 deca-

Naming Molecular Compounds

P2O5

diphosphorus pentoxide

COcarbon monoxide

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10 deca-

Writing Molecular Compounds

carbon tetrafluoride

CF4pentaphosphorus decoxide

P5O10

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?

CHAPTER 8

CHEMICAL BONDS The Structure of Metals

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CHAPTER 7,8. 6.1 IONIC BONDING 6.2 COVALENT BONDING 6.3 NAMING COMPOUNDS & WRITING FORMULAS 6.4 THE STRUCTURE OF METALS