Chemical Bonding

Metallic Bonding and Compounds

Metallic Bonds• Electrons are shared loosely• Electrostatic (positive-

negative) attraction between kernels (nuclei and non-

valence electrons) and a “sea” of free floating valence electrons

Check-In1. How are electrons shared in a metallic bond?2. What does the word “electrostatic” mean?3. What is a “kernel”?4. Why do we call the electrons a “sea” in a

metallic bond?

Metallic Bonding and Compounds

• Metal + metal• Conduct electricity and heat• Usually solid at room temp (range of m.p./b.p.) • Not soluble in water• Luster is shiny• Malleable and ductile

Characteristics of Compounds

Check-In1. How does the “sea” of mobile valence

electrons help explain at least one of the characteristics of metallic compounds?

Metallic Bonding and Compounds• Alloy: a mixture (usually a solid) that contains two or more elements and

has the characteristics of a metal• Compositions of Selected Alloys

– stainless steel 74% Fe, 18% Cr, 8% Ni, .18% C– coinage silver 90% Ag, 10% Cu– plumber’s solder 67% Pb, 33% Sn– brass 67% Cu, 33% Zn– 18 carat gold 75% Au, 10-20% Ag, 5-15% Cu– nichrome 60% Ni, 40% Cr

*note that the elements in an alloy are not present in specific ratios (the percentages may be adjusted)

Ionic Bonding and Compounds

Ionic Bonding• Electrons are transferred• Bond is an electrostatic attraction

between a cation and an anion (ions)

• atoms are often less stable than ions

• metals lose electrons to form positive ions to achieve stability cations– example: sodium

• non-metals gain electrons to form negative ions to achieve stability anions– example: chlorine

Check-In1. What happens to electrons in an ionic bond?2. Why do atoms lose or gain electrons?3. What holds an ionic bond together?4. What kind of elements lose electrons? What

kind gain electrons?

Ionic Bonding and Compounds

Characteristics of Compounds• metal + nonmetal• called “salts”• solids at room temperatures

(high m.p. and b.p.)• may dissolve in water to form

electrolytes (can conduct electricity)

• conduct electricity when molten (liquid at high temperature)

• brittle• crystalline, NOT molecules

– they form 3D crystal arrays of alternating anions and cations

Check-In1. What kind of elements make up an ionic

bond?2. What are ionic compounds called?3. In which two situations will ionic compounds

conduct electricity? Why do you think this is? (hint: what is electricity?)

4. What are two more properties of ionic compounds?

Chemical Formulas• Chemical formula- what elements it contains

and the ratio of the atoms of those elements– Example: NaCl (sodium chloride)Contains 1 sodium ion and 1 chlorine ion (chloride)

– Example: H2O (water)

• The formula is a combination of the symbols H and O and the subscript number 2

Contains 2 Hydrogen atoms and 1 Oxygen atom

Chemical Formulas• Subscript means “written below” and is written after the

symbol. • It tells how many atoms of that element are in one unit of the

compound. • If the symbol has no subscript, the unit contains only one

atom of that element.

Familiar Name Chemical Name FormulaBaking soda Sodium Bicarbonate NaHCO3

Battery Acid Sulfuric Acid H2SO4

Table salt Sodium Chloride NaCl

Vinegar Acetic Acid HCH3COO

Octet Rule• Octet Rule: atoms tend to gain, lose, or share electrons in

order to acquire a full set of valence electrons• Think of ionic bond formation as a process:

– electrons are lost/gained to achieve a stable octet of electrons– ions form – ions brought together by electrostatic attractions.

• Lewis Dot Diagrams:• Recall that a way to show and emphasize an atom’s valence

electrons is to draw the element’s dot diagram• Li Be N O Cl Si Ar

Covalent Bonding and Compounds

Covalent Bonds• electrons are shared tightly• electrostatic attraction between

electrons and nuclei

Check-In1. What happens to electrons in a covalent

bond?2. On your drawing of methane (CH4), draw

arrows showing what is attracted to what.3. Draw Lewis dot diagrams for two chlorine

atoms. Use circles to show how they might both get a full octet of electrons.

Covalent Bonding and Compounds

Characteristics of Compounds• nonmetal + nonmetal• solids/liquid/gas at room

temperatures (variable m.p. and b.p., generally lower than ionic compounds)

• may dissolve in water but doesn’t form an electrolyte

• doesn’t conduct electricity when solid or molten (liquid at high temperature)

• forms molecules

Check-In1. What kinds of elements participate in covalent

bonds?2. Which is the only nonmetal on the left side of

the periodic table?3. What are two ways covalent compounds behave

differently than ionic compounds? (hint: look back at your ionic notes)

4. What is the name of one piece of a covalent compound?

Covalent Bonding and Compounds• unshared pair - valence electrons that are not shared in bonds• single bond - only a single pair of electrons are shared between two atoms

(see examples above)• double bond - two pairs of electrons are shared between two atoms

– examples: formaldehyde- H2CO

oxygen- O2

• triple bond - three pairs of electrons are shared between two atoms– examples: nitrogen N2

ethyne, or acetylene, C2H2

Check-In1. How many single bonds are in the methane

molecule you drew earlier?2. How many unshared pairs are in the oxygen

molecule example?3. How many electrons are shared in a double

bond?4. Which do you think is the strongest bond,

single, double, or triple? Why?

Compounds• Compounds are substances made up of two or more

elements in fixed proportions.– Electrically neutral (equal numbers of positive and negative charges)– Atoms combine by gaining, losing, or sharing electrons to form

chemical bonds– Atoms achieve greater stability in bonding with other atoms

3 Types of bonding • Metallic– (metal + metal)

• Ionic– (metal + nonmetal)

• Covalent/molecular– (nonmetal + nonmetal)

Classify each compound as: M- Metallic

I- IonicC- Covalent

• KCl• Brass (Cu + Zn + Sn)• CO2

• NO2

• Sterling silver (Ag + Cu)• SnF2

• CH4

• MgCl2

• NH3

• LiF

Empirical vs. Molecular Formulas

• empirical formula – shows the lowest whole number ratio of atoms in a compound– always used for ionic compounds – can be useful for partially describing covalent compounds

• example: Ca2+ and F- combine to form CaF2

• molecular formula – shows the actual number of atoms in a single molecule – cannot be used for ionic compounds

• examples: sucrose- C12H22O11 and glucose- C6H12O6

• Questions: – What is the empirical formula for sucrose? – What is the empirical formula for glucose? ________