Covalent & Metallic

Bonding

Metallic Bonding

� Metals are made of closely packed cations.

� These cations have a number of valence electrons floating around them as what we call a “sea of electrons”.

� Metallic bonds are the attraction of the free-floating valence electrons for the positively charged metal cations.

� SHARING electrons

� Metallic bonds hold metals together.

� Properties

� good conductors, ductile, malleable

Covalent Bonding

� Covalent bond – attraction between two atoms because they

SHARE electrons

� In a covalent bond, atoms will SHARE electrons to fill their

octet, or to reach the electron configuration of noble gases.

� They will have FULL s and p orbital, just like ionic compounds.

� Octet rule satisfied!

� Sharing one pair of electrons creates a single covalent bond.

� Halogens form single covalent bonds

Molecules

� Covalent bonds form molecules.

� Molecule - group of neutral atoms held together with a covalent bond

� Diatomic molecules – molecule consisting of 2 atoms

� H2O2Br2F2I2N2Cl2

� Compound composed of molecules is a molecular compound.

Molecular Compounds

� Molecular Compounds Properties

� Gases or liquids

� Low melting/boiling points

� Usually made from 2 nonmetals bonded covalently

� Do not conduct electricity (solid or dissolved)

Molecular Formulas

� Molecular chemical formula shows how many atoms of each element a molecule contains.

� H2O – Molecular formula of water

�2 Hydrogen atoms, 1 Oxygen atom

� CO2 – Molecular formula for Carbon Dioxide

�1 Carbon atom, 2 Oxygen atoms

� H:H - Lewis Dot

� H-H – Structural Formula

� H2 – Molecular chemical formula

Lewis Structures Covalent Bonding

� To draw a Lewis Structure, one must know the types of atoms in the molecule, the number of atoms in the molecule and the number of valence electrons for each atom in the molecule.

Lewis Dot Structures

� Predict the location of certain atoms

� Least electronegative atom is usually the center atom

� Hydrogen is always a terminal atom

� Determine the number of electrons available for bonding

� Determine the number of bonding pairs

� Place the bonding pairs

� Determine the number of bonding pairs remaining

� Determine if the central atom satisfies the octet rule

Lewis Dot Structures

� My problem solving strategy:

� Draw Lewis dot structures for all elements in the

compound

� Element with the least electronegativity is usually center

atom

� Any lonely sad electrons want a friend! Pair them with

other sad lonely electrons

� Create bonding pairs!

� Check that all atoms satisfy octet rule

Double & Triple Covalent Bonds

� Sharing a pair of electrons creates a single covalent bond

� Sharing more than one pair of electrons creates double

and triple covalent bonds.

� 2 shared pairs – Double covalent bond

� 3 shared pairs – Triple covalent bond

� Carbon, Nitrogen, Oxygen

Naming Molecular Compounds

� We use a very different naming system for molecular compounds.

� Ionic compounds are named based on cations and anions.

� Molecular compounds don’t form ions.

� Can’t be named based on cations and anions!

� We use a prefix in a binary molecular compound to tell how many atoms of an element are present in the molecule.

Number Prefix

1 Mono-

2 Di-

3 Tri-

4 Tetra-

5 Penta-

6 Hexa-

7 Hepta-

8 Octa-

9 Nona-

10 Deca-

Naming Molecular Compounds

� Steps to naming

� Decide if the compound is molecular

(nonmetal and nonmetal) or ionic (metal and

nonmetal)

� If it’s molecular – follow rules below. If ionic,

use ionic naming scheme.

� Name the elements in order with the prefix

(how many).

� Omit mono if there is only one atom of the

first element.

� The ending of the second element will always

be –ide.

Number Prefix

1 Mono-

2 Di-

3 Tri-

4 Tetra-

5 Penta-

6 Hexa-

7 Hepta-

8 Octa-

9 Nona-

10 Deca-

Naming Molecular Compounds

� N2O – Dinitrogen Monoxide

� SO3 – Sulfur Trioxide

� N2O3 – Dinitrogen Trioxide

� CO – Carbon Monoxide

� CO2 – Carbon Dioxide