Ionic bonding

(Ch. 7 CP)( Do Block Actitivity) (Ch. TP)

Focus Question: How and why do elements combine?

Review:

What are valence electrons? ______

What is the octet rule? ______

What are cations and anions? ______

What is electronegativity? ______

Two types of compound formation at the atomic level:

1. Covalent Bonds - electrons are shared

2. Ionic bonds - electrons are transferred (“stolen”)

Ionic Bonds – occurs between metals (very low electronegativity) and non-metals (electronegative -high):

@ Nax + Cl:  Na+ + [ Cl ]- NaCl

Write new electron configuration for both.

@do electron configuration for Na and Cl ions. Then try Mg and Cl ions MgCl2.

The strong attractive forces between ions of opposite charges are called Ionic Bonds. The resulting compounds are called Ionic Compounds.

When these ions come together, they form crystals.

A Crystal is regular, repeating arrangement of atoms, ions, or molecules.

Properties of Crystals:

Strong attractive forces, high melting point, very hard and brittle, i.e. NaCl – cube shaped, 800°C.

Compounds are represented by formulas. For example:

NaCl – (sodium chloride) table salt

CuO (copper II oxide)

Fe2O3 – rust

H2O – water

Halide anions: Cl-, F-, etc. Group 7A

Chemical Formula (formula unit) -shows the kinds and numbers of atoms in the smallest representative unit of a substance.

Example: Fe2O3 – rust (formula unit – ionic compound)

H2O – water (molecule – Covalent compound)

Structural Formula – shows how the elements are joined.

Ball and Stick:

Space Filling Model:

Electron Dot Structure of K and O:

K. + K. + :O  K+ + K+ + O2-

CP: Guided Practice: p.193, 9,10 TP p. 131, 5.3 and 5.4

Charge/Oxidation Number: The charge on the ion when metals and nonmetals gain or lose electrons. Potassium has an oxidation number of 1+.

Bonding in metals:

Free floating valence electrons

Ionic Charges:

Group 1A, 2A, and 3A lose electrons – cations. Their ionic charge is positive and equal to their group number.

Group 5A, 6A, and 7A gain electrons – anions. Their ionic charge is negative and the number is equal

(Group # - 8 ). For example: Phosphorus

P(5 – 8) = P3-

Table 7.2 p. 192

The two non-metals in Group 4Ausually form molecular compounds. C and Si.

How do you write the formula for Ionic Cpds.?

Step 1) Write the symbol for the elements or polyatomic ions. (Cations are always first; anions are last.)

Step 2) Write the charge (oxidation #) for the elements or polyatomic ions.

Step 3) Drop the + or – sign, then criss-cross down the number only.

Step 4) Reduce the subscript if necessary

Step 5) Write the final answer.

Ex: Sodium Oxide

Na+1O-2  Na2O

Ex: Use this method to check that the compound is neutral.

Fe2O3, Iron(III) Oxide (binary ionic cpd) (What is this?)

Find the least common multiple:

Fe = +3 x 2 = +6O = -2 x 3 = -6

Fe3+ O2-charge = zero (0)

(p. 153, 26, 27)

Ternary compounds (3 elements):

Calcium Nitrate – Ca2+ and (NO3)-

Ca2+ (NO3)-  Ca(NO3)2

LiCN – lithium cyanide

Fe(ClO3)3 - Iron(III) Chlorate

NAMING IONIC COMPOUNDS:

Group A metals – name stays the same

Group B metals – name stays the same, but a roman numeral is added to show the charge (oxidation state).

Second element’s ending changes to ide.

Transition Metals: may have more than one ion.

Copper(I) and Copper(II) (stock names)

Cu +and Cu2+

Cuprous ion Cupric ion (classical)

(Table 5.4, p. 164) Page 255, 9.2

Guided Practice:

Lead, 4 electrons lost  Pb4+ Lead (IV)

Copper, 1 electron lost  Cu+ Copper (I)

Copper (I) chloride, Lead (IV) sulfide

PP: 16, 17, p. 145 cp

PP:p. 140, 5.27  TP

Polyatomic ions: composed of two or more atoms with a charge.

Sulfite – SO32-Sulfate – SO42-

(Table p. 257, Table 9.3 and Back of PT cp)(Table 5.6, p. 142 tp)

Indep. Practice: p. 258, #9 (cp)

Indep. Practice: p. 148, 5.37 (tp)

Binary Compounds: compounds composed of two elements. i.e. KCl (ionic)

Guided and Independent Practice

(p. 207, 45 )cp

(p.140, 5.23) tp

**Cp: p. 282, #67 a thru f

Important Vocabulary

Hydrates: When water molecules are chemically bonded to ionic cpds. CuSO4. 5 H2O (copper(II) sulfate pentahydrate).

Gypsum (buildings) CaSO4.2H2O

Applied Chemistry :

Hygroscopic substances - ionic substances that absorb water from the air. Sodium Carbonate (Na2CO3) and

Sodium Hydroxide (NaOH)

Deliquescent – substances that take enough water from the air to become liquids by dissolving completely.

What are desiccants and where are they found?

Desiccants are hygroscopic substances that are found in small packets usually with electronic equipment. (SiO2).

Other places???

Anhydrous Compounds – when a “hydrated” compound is heated so all the water molecules are driven off. Example: CuSO4. 5 H2O becomes CuSO4 (anhydrous)

(TP, Ch 5, p.133) (CP, Ch7, 196-198)

Ionic Properties:

Ionic compounds:

  • are composed of well-organized, tightly bond ions.
  • are crystalline solids at room temperature.
  • are hard, rough and brittle.
  • have high melting points due to the attractions between the positive and negative charges. (above 300°C)
  • dissolve in water and conducts electricity (electrolytes). Electrolytes are compounds that conducts electricity when melted or dissolved in water.
  • KCl, CuSO4, NaCl, NaHCO3

(salt sub., pools, salt, baking soda)

  • Representative Unit is a Formula Unit

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