IONIC electrons traded to form separate ions

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COVALENT electrons shared between a few nuclei distinct molecules

METALLIC electrons shared among all nuclei

13

Atoms (or ions) combine (bond) to form molecules (or compounds).

There are three forms of bonding.

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1. Valence electrons are involved in bonding

2. Octet rule: elements tend to gain, lose or share electrons so as to gain an inert gas configuration. (Duet for H and He) Ø 

IONIC COMPOUNDS share some Characteristic properties

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1.  low electrical conductivity as

solids (high as liquids) 2.  very high melting, boiling

points 3.  hard but brittle 4.  soluble only in polar solvents

(water)

•  distinct +/− ions •  ∞ crystal lattice •  strong omnidirectional

electrostatic bonds

By knowing properties, it is easier to distinguish Ionic vs. Molecular

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Ionic compound: a compound that consists of positive and negative ions. Metal + nonmetal (usually)

Molecular compounds: compounds consisting of individual molecules All nonmetals or nonmetals and metalloids.

Molecular compounds usually have low melting points

Ionic compounds have high melting points and are brittle.

Eg. NaCl K2SO4 Mg(NO3)2 NH4Cl

Eg. HCl H2O CH3COOH NH3

Ionic bonding occurs when ions combine to form compounds (salts).

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Electrons are exchanged to form separate ions with complete octets.

Ionic bond (interaction between the ions) is due to electrostatic attraction.

Coulomb's Law is place to start.

Lattice energy is the change in energy when an ionic solid is separated into

isolated ions in the gas phase.

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Lattice energy cannot be determined experimentally

How do we determine Lattice energy? Born-Haber cycle (10.8)

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Using known properties of atoms, lattice energy can be calculated. Process is known as the Born-Haber cycle.

Use Coulomb’s Law (charge and size) to explain trends in Lattice Energy

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LiF E = 1017 kJ MgO E = 3890 kJ Why the big difference???

dQQE 21!

Q1 +1 +2 Q2 −1 −2

d (0.76+ 1.33)/2 d= 1.045Å

(0.72 + 1.40)/2 d =1.06Å

E

Use Coulomb’s Law (charge and size) to explain trends in Lattice Energy

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What if the charge is the same? Q1Q2 = −1 for all of these salts d

QQE 21!

LiI NaI KI d= 1.48Å d= 1.61Å d= 1.79Å

Ion sizes are important in ionic bonds.

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Which has the greatest lattice energy? (How do you know?) NaF NaCl NaBr NaI

lattice energy can’t be measured: what can we measure that is related to lattice energy?

Melting point increases as lattice energy increases.

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mp NaF 993oC NaCl 801oC NaBr 747oC NaI 661oC MgO 2800oC

TRANSITION METAL IONS are exceptions to octet rule.

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•  s electrons are part of valence electrons

•  transition metals can have variable charges.

When forming an ion: •  s electrons are lost first •  then maybe d electrons

Naming Inorganic Compounds and Ions

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Name Formula potassium ion

CO32−

ammonium ion sodium bicarbonate

H2SO4 " Combine Ca+2 and PO4

3−

Cu(II) and sulfate ion

See Section 5.4 Tables 5.2, 5.10