What Is a Metallic Bond ?

Bonding Notes

What is a metallic bond ?

• Occurs when both atoms have ______ionization energies and ______electronegativities and will lose electrons easily (i.e. 2 metals) • In metallic bonding, positive metal ions are arranged with valence electrons ______around them. • Since the electrons are delocalized, they are ______and able to move throughout the metal structure.

Properties of Metallic Compounds

1. ______and ______because atoms are not restricted to one position by a fixed bond and the ions can roll past each other.

2. ______conductors of heat and electricity because the electrons are mobile and can transmit energy rapidly.

3. Shiny because when light strikes a metal, the valence electrons ______energy, oscillate at the same frequency as the incident light (incoming light) and then emit light as a reflection of the original light.

4. ______at room temperature (except mercury) due to the strong bonds (intermolecular and intramolecular forces are the same).

5. They exhibit the ______effect which is electron emission caused by ______or light. This occurs when the energy of light striking a metal is sufficient to overcome the attractive forces and an electron escapes the metal.

IONIC BONDS

 Occur between an element with ______ionization energy (a metal) and an element with ______ionization energy (a non-metal).

 An actual ______of electrons from the metal (becoming a cation) to the non-metal (becoming an anion) occurs.

 This transfer results in the formation of 2 oppositely charged ______.

 The ______interaction between the 2 ions holds the compound together.

Properties of Ionic Compounds 1. ______at room temperature because the attraction between the ions is very strong.

2. The intramolecular forces are ______the intermolecular forces (i.e. the electrostatic attraction of oppositely charged ions)

3. Atoms are arranged in a highly ordered crystal ______structure which maximizes the attractive forces between oppositely charged ions and minimizes the repulsion between like charged ions (the crystal structures are determined experimentally using X-ray crystallography).

4. ______in water (the ions will dissociate in water).

5. Will ______electricity as a liquid or aqueous solution because the ions are free to move to oppositely charged electrodes. Use orbital diagrams to show the formation of an ionic bond:

Between Oxygen and sodium

COVALENT BONDS

 Occur between 2 atoms with ______ionization energies (i.e. 2 non-metal atoms).  Result from a ______of electrons to obtain a full outer energy level (octet rule).  If the ______difference between the two atoms is less than 0.4, the bond is a true covalent bond and the electrons are shared ______.

 If the ______difference between the two atoms is between 0.4 and 1.7, the bond is polar and there is an unequal sharing of electrons.

 If a molecule contains polar covalent bonds and is ______, the molecule will be polar.

 If both electrons being shared come from the same atom, the bond is a ______covalent bond. Properties of Polar Covalent Molecules

1. Since these compounds exhibit polarity or ______, their intermolecular forces will be ______than non-polar covalent compounds (the presence of dipole-dipole forces and possibly H- bonding).

2. These compounds will have ______melting and boiling points and are more likely to be liquids or solids at room temperature (may even exhibit a crystal lattice like sugar).

3. Will dissolve in polar solvents if ______is present (sugar in water).

4. Will ______electricity to any appreciable degree (only ionize to a very small degree)

Properties of Non-Polar Covalent Compounds

1. Have ______melting and boiling points and are usually gases at room temperature. This is due to the low intermolecular forces that exist in these molecules (London Dispersion Forces only).

2. If solid at room temperature, the solid is usually ______.

3. Soluble in ______solvents such as ethers.

4. Will not conduct electricity in any form due to the fact that there are no ______present. Use orbital diagrams to show the formation of a covalent bond:

Carbon and Hydrogen to form CH4

Carbon and Hydrogen to form C2H4

LEWIS STRUCTURES

Follow Step by Step Method 1. Total all valence electrons. [Consider Charge] 2. Write symbols for the atoms and guess skeleton structure [ define a central atom ]. 3. Place a pair of electrons in each bond. 4. Complete octets of surrounding atoms. [ H = 2 only ] 5. Place leftover electrons in pairs on the central atom. 6. If there are not enough electrons to give the central atom an octet, look for multiple bonds by transferring electrons until each atom has eight electrons around it.

Non-Octet Compounds • Some compounds will contain central atoms that do not follow the octet rule. • The four possibilities for non-octet compounds are:

– Where more than 4 atoms are bonded to the central atom such as PCl5.

– A noble gas is participating in bonding such as XeF4.

– Where the central atom has less than 8 valence electrons such as BH3. – Where molecules contain an odd number of nonbonding electrons such as NO.

Resonance Structures • For some molecules, there are multiple ways of placing the electrons between the atoms. • Structures that differ only in the arrangement of the electrons are called RESONANCE STRUCTURES. • Resonance structures are indicated using a double headed arrow.

Coordinate Covalent Bonds • A coordinate covalent bond results when both electrons in the bond are donated from the same atom. • To determine if a bond is coordinate covalent, compare the number of nonbonding electrons around an atom to the number of valence electrons the atom has. SummarySummary ofof VSEPRVSEPR MolecularMolecular ShapesShapes e-pairs Notation Name of VSEPR shape Examples

2 AX2 Linear HgCl2 , ZnI2 , CS2 , CO2

3 AX3 Trigonal planar BF3 , GaI3

AX2E Non-linear (Bent) SO2 , SnCl2 - 4 AX4 Tetrahedral CCl4 , CH4 , BF4 - AX3E (Trigonal) Pyramidal NH3 , OH3

AX2E2 Non-Linear (Bent) H2O , SeCl2

5 AX5 Trigonal bipyramidal PCl5 , PF5

AX4E Distorted tetrahedral TeCl4 , SF4 (see-sawed)

AX3E2 T-Shaped ClF3 , BrF3 - - AX2E3 Linear I3 , ICl2 - 6 AX6 Octahedral SF6 , PF6

AX5E Square Pyramidal IF5 , BrF5 - - AX4E2 Square Planar ICl4 , BrF4

Shapes of molecules

A molecule consists of 2 or more atoms joined by covalent bonds.

The shape of a molecule is a description of the way the atoms in the molecule occupy space.

A diatomic molecule, a molecule composed of only 2 atoms, must always be linear in shape as the centers of the 2 atoms will always be in a straight line.

'Electron Cloud' Repulsion Theory (Valence Shell Electron Pair Repulsion, VSEPR) is used to predict shapes and bond angles of simple molecules

a. an 'electron cloud' may be a single, double or triple bond, or a lone pair of electrons b. a lone pair of electrons is a non-bonding pair of electrons c. 'electron clouds' are negatively charged since the electrons are negatively charged, so electron clouds repel one another and try to get as far away from each other as possible d. lone pairs of electrons exert a greater repelling effect than bonding pairs do e. lone pair-bonding pair repulsion is greater than bonding pair-bonding pair repulsion f. lone pair-lone pair repulsion > lone pair-bonding pair repulsion > bonding pair-bonding pair repulsionVSEPR Model (Figure 9.6)

• To determine the electron pair geometry: • draw the Lewis structure, • count the total number of electron pairs around the central atom, • arrange the electron pairs in one of the above geometries to minimize e-e repulsion, and count multiple bonds as one bonding pair. VSEPRVSEPR ModelModel LEWIS STRUCTURES 1. Draw the Lewis structure or diagram for the following substances:

1) ZnI2

2) CS2

3) SnCl2

4) CCl4

5) NH3

6) SeCl2

7) PCl5

8) SF4

9) ClF3

10) SF6

11) BrF5 - 12) I3 - 13) ICl4 - 14) ICl2

15) BF3 2- 16) SO4

2. Determine the shape of each molecule above according to the VSEPR Theory.