Chemical Bonding

Chemical bond – The attractive force between the protons of one atom for the electrons of another atom

Determined by electronegativity

Chemical energy – a type of stored (potential) energy that is involved in the formation and breaking of chemical bonds.

When bonds break... energy is absorbed!CuSO4·5H2O + energy → CuSO4 +

5H2O ↑ breaking this bond by adding energy!

BondingWhen bonds form... energy is released!Mg + O → MgO + Energy

Bonding & EnergyWhen bonds form, energy is released. Systems are more stable when they are at lower energy levels.

Therefore, atoms become morestable when they form bondsdue to the release of energy.

BondingWhy do atoms bond?

to become more stableto fill their valence shell(highest principal

energy level)It takes eight electrons to fill the valence shell,

except for elements that only need two.

What group of elements do not bond?Noble Gasestheir outer shell is already completely filled.

The Octet Rule- Atoms bond in order to have eight electrons in their valence shells(or sometimes two), giving them the same electronic configuration as a noble gas.

Noble gases are stable. All elements want to be like the noble gases.

Bonding Ionic Bond – the bond that forms between metal and

nonmetal. Electrons are transferred from the metal to the non-metal. The bond between cation and anion is very strong. Determines physical and chemical properties of ionic

substances Ionic Substances

Called "Salts" solids form a crystalline shape called a “lattice” High melting points (solid at room temp.) brittle solubility – ability to be dissolved.

Ionic compounds dissolve in water aqueous – dissolved in water

Salts do not conduct electricity as solids Do conduct when melted(liquid) or aqueous

electricity is a flow of charged particles Ions(charged atoms) move freely when liquid or aqueous

Ionic Compounds- Oxidation state : the charge of the ion.

• Metals lose electrons and become positive• Nonmetals gain electrons and become negative

• The number of electrons lost or gained determines oxidation state

• Ex: Ca is in Group 2, has 2 valence electrons• becomes Ca2+

• Therefore, its oxidation state = 2+• Ex: N is in Group 15, has 5 valence electrons

• becomes N3-

• Oxidation state = 3-

• Several metals have more than one oxidation state• Many are transition metals• Example:

• Copper can have one valence electron:• Copper can also have 2 valence electrons:

Cu+

Cu2+

Lewis-Dot Diagrams Lewis-Dot diagrams

aka electron-dot diagrams or Lewis-Dot Structures Shows valence electrons for atoms

Maximum number of valence electrons = 8 (think Octet Rule)

Valence electrons are drawn around the outside of the element symbol

The first 4 electrons are filled one to each side(top, right, bottom, left)

The next 4 electrons pair up with the first 4 after that Example: Xenon is a noble gas, it has 8 valence electrons.

Xe

Lewis-Dot Diagrams & BondingCan assist in determining how elements bond

Metals lose electrons Nonmetals gain electrons Dot diagrams show where and how many electrons are being

transferred 1. Determine the number of valence electrons for each

element and draw them in 2. Transfer electrons from the metal to the nonmetal 3. Determine if more than one ion is needed to fill the

valence shell 4. Write the metal first with its oxidation state 5. Write the non-metal second with a full outer shell and

brackets 6. Add coefficients if more than one atom was used

Na

Na+[ O ]2-2

O

Na

Chemical Formulas Chemical formula- expression indicating the elements in

the compound and how many in the smallest unit of a substance “Which atoms & how many”

Subscripts indicate how many but 1s are not written Ex. NaCl Ex. Fe2O3

Oxidation states can be determined from formulas Chemical formulas are neutral

Anion & cation charges must total to 0 Start with the ion you know for sure

Example: NaCl Na is Group 1 & always forms a 1+ ion. Therefore, Cl must be 1- to balance it.

Example: Fe2O3

· Fe is a transition metal, oxidation state is unknown· O is Group 16 & always forms 2- ion, and there are 3· Fe must be a 3+ in order to balance the negative

charges of O 

one Na atom and one Cl atomtwo Fe atoms and three O atoms

IUPAC Naming System Binary Compound – two different elements chemically combined

Two parts: Cation (metal) & Anion (nonmetal) Ternary compounds – compounds with more than two elements.

Polyatomic ion replaces an anion(or cation) Polyatomic ions – ions made from more than one element

Often made from multiple nonmetals Most end in “-ate” or “-ite” List on Page 7 of NC Reference Tables

IUPAC - International Union of Pure and Applied Chemists These guys made the naming system

1. Cation is written first. Ending does not change2. Anion is written second.

• If it’s a nonmetal, ending is changed to “-ide”• If a polyatomic ion, ending is not changed

3. Certain Transition metals need a roman numeral• “Ti through Cu, Au, Hg, Sn & Pb”

Examples: Sodium & chlorine Calcium & Oxygen Magnesium and sulfate Iron (II) and bromine

Sodium chloride Calcium oxide Magnesium sulfate Iron (II) bromide

Chemical Naming & Chemical Formulas Determining a name from a formula

Same rules for naming; Cation first, anion second, roman numerals for transition metals

The amount indicated by subscripts doesn’t factor into the chemical name for ionic compounds

o Example: MgBr2

Li2SO4

CuO

Determine a formula from a chemical name Write the symbols for the cation & anion Look up the charges. Roman numerals indicate the

charge on transition metal Calculate the amount of each ion and fill in subscripts

Magnesium bromideLithium sulfateCopper (II) oxide

Metallic Bonds Positive metal ions surrounded by valence

electrons Valence electrons are held loosely, flow freely

between ions “positive ions in a sea of mobile electrons” The bond is a result of the attraction between the

positive ions and the mobile electrons.

The delocalized valence electrons give metals their properties

Luster, Malleability, Ductility, ability to conduct heat and electricity in the solid state.