IONIC AND METALLIC BONDING

Chapter 7

Objectives

You WILL be able to…Determine number of valence electrons in an atom

of a representative elementExplain how the octet rule applies o atoms of

metallic and nonmetallic elementsDescribe how cations formExplain how anions formExplain the electrical charge of an ionic compoundDescribe 3 properties of ionic compoundsModel the valence electrons of metal atomsDescribe the arrangement of atoms in metalExplain the importance of alloys

Ions

Valence Electrons – Electrons in the highest occupied energy level of an element’s atoms

The number of valence electrons determines an element’s properties

Group number indicates the number of valence e-

The Octet Rule- the achievement of 8 electrons in the highest energy level of an atom

Done by losing, gaining, or sharing valence electrons

Formation of Cations

Cations form when atoms lose valence electronsMetals usually do this because they only have a few

valence electrons and they have low ionization energies

The loss of valence electrons makes the cation more stable than the atom because there is an complete octet in the valence shell

For example:Na = 1s22s22p63s1 and Na + = 1s22s22p6

Monatomic cations are named using the name of the element (ie sodium ion, magnesium ion)

Some metals that easily give up valence electrons are…

Alkali metals (+1 charge)Alkali Earth Metals (+2 charge)Aluminum (+3 charge)Heavier group IV and V elements (Sn +2 or +4; Pb

+2 or +4; Bi +3)Most transition and inner transition elements (Ag+1,

Zn +2, Cr +3; most rare earth metals +3)Some transition metals have cations with varying

charge depending on what they are bonded with (ie Fe +3 and Fe+2)

Formation of Anions

Anions form when atoms gain valence electrons

The gain of valence electrons makes the anion more stable than the atom because there is now a complete octet in the valence shell

For example:Cl = 1s22s22p63s23p5 and Cl -

=1s22s22p63s23p6

Anions are named using the root of the element’s name plus the ending –ide (ie. bromide, chloride)

Some nonmetals easily acquire electrons…Halogens (-1 charge)Chalcogens (-2 charge)Nitrogen (-3 charge)

Polyatomic Ions are comprised of two or more atoms covalently bonded that can be considered as acting as a single particle

Ionic Bonds and Ionic Compounds

Ionic bonds are formed when the charges on positive ions balance the charges on the negative ions through electrostatic attraction

Formula units are the lowest whole number ratio of ions in an ionic compound.

Chemical formulas are shorthand ways of showing the amounts and the types of elements in the smallest representative unit

Example: NaCl, CaBr2, AlI3 (salts)

Electron Dot Formulas-Open and closed circles or x’s

Ionic attractions are so strong that almost all ionic compounds are solid with unique crystalline structures

The strength of the bonds also leads to high melting points and boiling points

Ionic bonds almost always occur between metals and nonmetals

Ionic compounds are also good conductors of electricity if dissolved in water or molten

Ionic compounds are electrically neutral, therefore the number of positive charges is the same as the number of negative charges.

Colors of Ionic Compounds

Transition metal ions having partially filled d orbitals usually have a color.

For example…NiSO4

FeCl3

CuSO4

Metal cations that have no d electrons or completely filled d orbitals are usually not colored.

NaCl MgSO4

CaCl2 ZnCl2

Metals in Bonding

Metals have loosely held valence electronsWhen metal atoms exist in the solid form of a

metal all the nuclei share all the valence electrons of all the atoms in the sample

“Electron Sea”

The “sea of electrons” explains physical properties such as conductivity, malleability, and ductility

Metals are arranged in compact and orderly patterns

Alloys

Mixtures of two or more elements where at least one is a metal

Steel, brass (Cu and Zn), bronzeMixing alloys will result in a metal with

superior properties than those of the component materials

Them’s 22’s son!!!