1. Chemical Bonding

2. Metallic Bonding and Compounds
Metallic Bonds
Characteristics of Compounds
Electrons are shared loosely
Electrostatic (positive-negative) attraction between kernels (nuclei and non-valence electrons) and a “sea” of free floating valence electrons
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

3. 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 % Fe, 18% Cr, 8% Ni, .18% C
coinage silver 90% Ag, 10% Cu
plumber’s solder 67% Pb, 33% Sn
brass % Cu, 33% Zn
18 carat gold % 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)

4. Ionic Bonding and Compounds
Characteristics of Compounds
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
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

5. Covalent Bonding and Compounds
Covalent Bonds
Characteristics of Compounds
electrons are shared
electrostatic attraction between electrons and nuclei
nonmetal + nonmetal
solids/liquid/gas at room temperatures (variable m.p. and b.p.)
may dissolve in water but doesn’t form an electrolyte
doesn’t conduct electricity when solid or molten (liquid at high temperature)
forms molecules

6. 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

7. 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

8. 3 Types of bonding Metallic (metal + metal) Ionic (metal + nonmetal)
Covalent/molecular
(nonmetal + nonmetal)

9. Classify each compound as: M- Metallic I- Ionic C- Covalent
KCl
Brass (Cu + Zn + Sn)
CO2
NO2
Sterling silver (Ag + Cu)
SnF2
CH4
MgCl2
NH3
LiF

10. Chemical Formulas
Chemical formula- what elements it contains and the ratio of the atoms of those elements
Example: NaCl (sodium chloride)
Contains 1 sodium atom and 1 chlorine atom
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

11. 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
Formula
Lye
Sodium Hydroxide
NaOH
Ammonia
NH3
Sand
Silicon Dioxide
SiO2
Battery Acid
Sulfuric Acid
H2SO4

12. 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

13. 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? ________