Bonding

® Chemical Bonds: are the forces that link atoms together

® The electron configuration determines how atoms bond

® Ionic Compound: a compound that is composed entirely of ions

® Cations: positively charged ions

® Metals form cations

® Anions: negatively charged ions

® Nonmetals form anions

® Almost any combination of anions and cations can form an ionic bond

Monatomic Ions

® Binary Ionic Compounds: contain ions of only 2 elements

Criss Cross Method to write formulas for Binary Ionic Compounds

More Criss Cross Examples

® Barium Sulfide

l Ba S

^l Ba⁺² S^-2

_l Ba₂S₂ - simplify

_l Ba₁S₁ – remove 1s

l BaS

® Calcium Nitride

l Ca N

^l Ca⁺² N^-3

_l Ca₃N₂

Transition Metals:

® do not follow the octet rule and commonly form more than one monatomic cation

® Use Roman Numerals to distinguish the cations of transition metals

® Fe⁺² = Iron (II) Fe⁺³ = Iron (III)

® Cu⁺¹ = Copper (I) Cu⁺² = Copper (II)

Writing Formulas for Transition Metals

– Iron (II) Sulfide

– Fe S

^– Fe⁺² S^-2

_– Fe₂S₂ - simplify

_– Fe₁S₁ – remove 1s

– FeS

– Iron (III) Sulfide

– Fe S

^– Fe⁺³ S^-2

– Fe₂S₃

Polyatomic Ions:ions formed from a group of elements

Writing Formulas with Polyatomic ions

– Magnesium Nitrate

_– Mg NO₃

^– Mg⁺² NO₃^-1

– Mg₁ (NO₃)₂

Note: Use parantheses around polyatomic ion to show subscript is for the entire ion

_– Mg (NO₃)₂

– Ammonium Carbonate

_– NH₄ CO₃

^– NH₄⁺¹ CO₃^-2

– (NH₄) ₂ (CO₃)₁

_– (NH₄)₂ CO₃

No parantheses needed around CO₃ because there is only one CO₃ ion

Oxidation Numbers

® Show the combining capacity of an element.

® Tells how many electrons an atom gains or loses when forming a compound.

Ex. Sodium has one electron in the valence shell. It will become more stable when it gives away this electron. When an atom of sodium loses an electron it becomes a positive ion with a +1 charge. The oxidation number of sodium is 1+.

^® This would be represented as: Na ¹⁺

Oxidation Numbers as a Trend

Covalent Bonds

® A Covalent Bond is formed by a shared pair of electrons between 2 atoms

® Covalent Bonds usually form between 2 nonmetals

® Molecule: a group of atoms that are united by covalent bonds

® Molecular Substance: a substance that is made of molecules

Writing Formulas for Molecular (Covalent) Substances

® Use the prefix to determine the subscript. If there is no prefix for the first element there is only one atom of that element.

® Examples:

_® dihydrogen tetranitride = H₂N₄

® carbon monoxide = CO

_® carbon tetrachloride = CCl₄

Lewis Dot Structures Con’t

Lewis Dot Structures for Group 1A-8A

Lewis Dots and Ionic Bonds

Ionic Bonding Example 2
Each Lithium atom has transferred one electron to the Nitrogen atom forming Li₃N

Describing Covalent Bonds

® The Octet Rule Applies: atoms share electrons to obtain 8 valence electrons

® The shared pair completes the octet for both atoms

® H only needs 2 electrons to fill its outer shell

® The group number of the atom determines the number of shared pairs that an atom needs

Group 4A 5A 6A 7A

Desired # of shared pairs 4 3 2 1

Lewis Dot Structures and
Covalent Bonds

l Draw Lewis Structures for each atom

l Count the total number of valence electrons

l Place the atom that requires the most shared pairs in the center

l Draw one covalent bond to connect the central atom to each of the other atoms

l Check to see that all atoms have octet and total valence electrons is the same as step 2

Lewis Dot Example: NCl₃

l Lewis Structures

l Total Valence e^- = 26

l N needs 3 shared pairs, Cl needs 1, N is central

l Draw one shared pair between N and each Cl

l All atoms have a full octet and total e^- = 26

Dashes can be used to represent bonds

Lewis Dot Structures

® Atomic Models used to represent atoms forming chemical bonds.

® Consists of the element’s symbol and the atom’s valence electrons.

® Symbol = kernel (represents the protons, neutrons and full electron shells).

® Dots = valence electrons.

Covalent Bonds

® Electrons are shared

® Occur between two nonmetals

® Each atom simultaneously attracts the electrons that are being shared

Use Dot
Structures

H H

Cl Cl

H Cl

® Diatomic Molecules: When two atoms of the same element form covalent bonds

® Examples:

_® H₂

_® Cl₂

Bonding

® Chemical Bonds: are the forces that link atoms together

® The electron configuration determines how atoms bond

® Ionic Compound: a compound that is composed entirely of ions

® Cations: positively charged ions

® Metals form cations

® Anions: negatively charged ions

® Nonmetals form anions

® Almost any combination of anions and cations can form an ionic bond

Monatomic Ions

® Binary Ionic Compounds: contain ions of only 2 elements

Criss Cross Method to write formulas for Binary Ionic Compounds

More Criss Cross Examples

® Barium Sulfide

l Ba S

^l Ba⁺² S^-2

_l Ba₂S₂ - simplify

_l Ba₁S₁ – remove 1s

l BaS

® Calcium Nitride

l Ca N

^l Ca⁺² N^-3

_l Ca₃N₂

Transition Metals:

® do not follow the octet rule and commonly form more than one monatomic cation

® Use Roman Numerals to distinguish the cations of transition metals

® Fe⁺² = Iron (II) Fe⁺³ = Iron (III)

® Cu⁺¹ = Copper (I) Cu⁺² = Copper (II)

Writing Formulas for Transition Metals

– Iron (II) Sulfide

– Fe S

^– Fe⁺² S^-2

_– Fe₂S₂ - simplify

_– Fe₁S₁ – remove 1s

– FeS

– Iron (III) Sulfide

– Fe S

^– Fe⁺³ S^-2

– Fe₂S₃

Polyatomic Ions:ions formed from a group of elements

Writing Formulas with Polyatomic ions

– Magnesium Nitrate

_– Mg NO₃

^– Mg⁺² NO₃^-1

– Mg₁ (NO₃)₂

Note: Use parantheses around polyatomic ion to show subscript is for the entire ion

_– Mg (NO₃)₂

– Ammonium Carbonate

_– NH₄ CO₃

^– NH₄⁺¹ CO₃^-2

– (NH₄) ₂ (CO₃)₁

_– (NH₄)₂ CO₃

No parantheses needed around CO₃ because there is only one CO₃ ion

Oxidation Numbers

® Show the combining capacity of an element.

® Tells how many electrons an atom gains or loses when forming a compound.

Ex. Sodium has one electron in the valence shell. It will become more stable when it gives away this electron. When an atom of sodium loses an electron it becomes a positive ion with a +1 charge. The oxidation number of sodium is 1+.

^® This would be represented as: Na ¹⁺

Oxidation Numbers as a Trend

Covalent Bonds

® A Covalent Bond is formed by a shared pair of electrons between 2 atoms

® Covalent Bonds usually form between 2 nonmetals

® Molecule: a group of atoms that are united by covalent bonds

® Molecular Substance: a substance that is made of molecules

Writing Formulas for Molecular (Covalent) Substances

® Use the prefix to determine the subscript. If there is no prefix for the first element there is only one atom of that element.

® Examples:

_® dihydrogen tetranitride = H₂N₄

® carbon monoxide = CO

_® carbon tetrachloride = CCl₄

Writing Covalent Formula

Carbon Dioxide

® Write the name of each element.

C O

® Add the subscripts as indicated by the prefixes.

CO₂

Try these examples

® Sulfur dioxide

® Sulfur monoxide

® Carbon tetrachloride

® Dihydrogen dioxide

® Nitrogen triiodide

Naming Covalent Molecules

NH₃

® Name first nonmetal – use subscript to determine prefix

Nitrogen (No prefix written for the first element IF it is a one.)

® Name second nonmetal use subsripts to determine prefix and change the ending to -ide.

Trihydride

® Name of the molecule: Nitrogen trihydride

Example

P₂O₅

® Name First Nonmetal with prefix

Diphosphorus

® Name second nonmetal with prefix and ide ending

Pentoxide

® Name the molecule: Diphosphorus Pentoxide

Try these Examples

® CO

_® CO₂

_® SF₂

_® PI₃

® H₂O

Predicting Bond Types

® Metal and Nonmetal => Ionic

® Nonmetal and Nonmetal => Ionic

Predict type of bond for:

® Mg and F

® O and Cl

® Br and Br

Covalent Compounds Prefixes

® mono one

® di two

® tri three

® tetra four

® penta five