Chemical Bonding

• Review• All atoms have valence electrons• Valence electrons- the electrons in

the outermost energy level• Atoms that give up electrons become

positive and are called cations• Atoms that gain electrons become

negative and are called anions• Atoms with the same number of

valence electrons have similar chemical properties

Chemical Bonding• All the elements want to be like the Noble gases.

• They’re chemically stable• They have a full outer shell

• How do atoms go from being unstable to stable?• Elements will form bonds with other elements in order to

become stable

• A chemical bond is formed when two substances are more stable when bonded than they were before the bond.

• When a bond is formed, energy is released!• Magnesium Demonstration:

Mg + O → MgO + light & heat

Bonding• When bonds break... energy is absorbed!

• CuSO4 · 5H2O + energy → CuSO4 + 5H2O ↑

This bond is broken by adding energy!

• Chemical energy is the energy involved that is either produced or absorbed when forming or breaking chemical bonds.

Chemical Bonding• Atoms gain stability by releasing energy. The

more energy released, the greater the stability.• Therefore, atoms become more stable when

they form bonds due to the release of energy.

Energy Released

Sta

bili

ty

Bonding• Atoms bond in order to be like the Noble Gases

• They follow 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 do not bond• Their outer shell is already completely filled.

• Metals will lose valence electrons so that their (full) inner shell becomes their valence shell

• Nonmetals will gain electrons to fill their outer shell.• The type of bond is determined by each elements’ electronegativity.

• Elements with a large difference in electronegativities will form ionic bonds (metals & nonmetals)

• Nonmetals with similar electronegativities will form covalent bonds

Ionic BondingIonic Bond– the bond that forms between metal and nonmetalElectrons are transferred from the metal to the nonmetal.The bond between cation and anion is very strong.Determines chemical & physical properties of ionic compounds

Ionic Compound – Any substance formed from the bond between cation and anion. Also called a salt.

Physical Properties of ionic compounds high melting points due to strong bond between cation & ion Crystalline shape called lattice

Brittle soluble – can be dissolved in water. Once dissolved, it is called an

aqueous solution. Salts do not conduct electricity as solids

Do conduct when melted (liquid) or aqueous electricity is a flow of charged particles Ions (charged atoms) are able to flow freely when in a liquid or

aqueous state

Ionic BondingLattice Structure of NaCl

Electricity

electrons in a metal wire ions in solution

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-

• Some 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:

The d-shell of the transition metals allow for multiple variations of valence electrons

Cu+

Cu2+

Lewis-Dot DiagramsLewis-Dot diagrams•Also called:

• electron-dot diagrams• Lewis-Dot Structures

•Comprises of the Element symbol and the valence electrons•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.

• Draw the Lewis Dot Structures for H, Ca, Al, C, Se, Br, and Ne

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 - Ductility- Malleability - good conductors of heat & electricity