Chemical Bonding

and Nomenclature

Chemical Reactivity

• How much an element reacts depends on

the electron configuration of its atoms.

• Every element wants 8 valence electrons.

• Oxygen only has six, so it wants two more

• Neon already has eight.

Chemical Reacitivity

• Neon is a noble gas.

• The noble gases, which are found in Group

18 of the periodic table, show almost no

chemical reactivity.

• The noble gases have filled outer energy

levels.

Review of Valence Electrons

• Remember that valence electrons are the

electrons in the OUTERMOST energy level

• B is 1s22s22p1

– Outer energy level is 2

– There are 2 + 1 = 3 electrons in energy level 2

– These are the valence electrons.

• Br is [Ar] 4s23d104p5

– How many valence electrons are present?

Valence Electrons

• All atoms are uncharged because they have equal

numbers of protons and electrons.

• For example, a potassium atom has 19 protons and

19 electrons.

• After giving up one electron, potassium still has

19 protons but only 18 electrons.

• Because the numbers are not the same, there is a

net electrical charge.

Octet Rule

• In most chemical reactions, atoms tend to

match the s and p electron configurations of the

noble gases.

• This tendency to have either empty outer

energy levels or full outer energy levels of eight

electrons is called the octet rule.

– Potassium after it loses one electron has the same electron configuration as chlorine after it gains one.

– The atoms of many elements become stable by achieving the electron configuration of a noble gas.

• An ion is an atom, radical, or molecule that has

gained or lost one or more electrons and has a

negative or positive charge.

• An ion with a positive charge is called a cation.

• An ion with a negative charge is called an anion.

Ions

Predicting Ionic Charges

Group 1: Lose 1 electron to form 1+ ions

H+ Li+ Na+ K+

Group 2: Loses 2 electrons to form 2+ ions

Be2+ Mg2+ Ca2+ Sr2+ Ba2+

Predicting Ionic Charges

Group 13: Loses 3

electrons to form

3+ ions

B3+ Al3+ Ga3+

Predicting Ionic Charges

Group 14: Lose 4

electrons or gain

4 electrons?

Neither! Group 13 elements rarely form ions.

Predicting Ionic Charges

Group 15: Gains 3

electrons to form

3- ions

N3-

P3-

As3-

Nitride

Phosphide

Arsenide

Predicting Ionic Charges

Group 16: Gains 2

electrons to form

2- ions

O2-

S2-

Se2-

Oxide

Sulfide

Selenide

Predicting Ionic Charges

Group 17: Gains 1

electron to form

1- ions

F1-

Cl1-

Br1- Fluoride

Chloride

Bromide

I1- Iodide

Predicting Ionic Charges

Group 18: Stable Noble gases do not form ions!

Predicting Ionic Charges

Groups 3 - 12: Many transition elements

have more than one possible oxidation state.

Iron(II) = Fe2+ Iron(III) = Fe3+

Predicting Ionic Charges

Reviewing Types of Ions

• Cation – A positively charged particle

• Elements with almost empty valence shells (metals lose

electrons to become positively charged

• The overall charge on the ion is positive due to excess

positive nuclear charge (protons do NOT change in

chemical reactions).

• Anion – A negatively charged particle

• Elements with almost full valence shells (non-metals)

tend to gain electrons to become negatively charged.

• The overall charge on the ion is negative because of the

gain, and therefore excess, of negative electrons.

More than two elements

• Instead of having ions made of a single atom, many

ionic compounds have groups of atoms that are ions.

• A polyatomic ion is a charged group of two or more

bonded atoms that can be considered a single ion.

– Polyatomic ions work in the same way as simple ions

– Covalent bonds hold the polyatomic ion together so it

behaves as a unit

Some Polyatomic Ions:

Chemical bond

• The force of electrical attraction

that holds together the atoms in

compounds

• There are three general types of

bonding

– Ionic

– Covalent

– Metallic

Ionic Bonding

• An ionic bond is formed by a metal and a nonmetal

• Ionic bonds are formed by one atom transferring electrons to another atom to form ions.

– The force of attraction between the 1+ charge on the

sodium cation and the 1 charge on the chloride

anion creates the ionic bond in sodium chloride.

– Example: sodium chloride is a salt, the scientific

name given to many different ionic compounds.

An atom of sodium

transfers the electron in

its outer shell to an atom

of chlorine.

The oppositely charged sodium and chloride ions are

attracted to one another, forming sodium chloride.

Having given up

an electron,

sodium becomes a

positively charged

ion.

Having received an

electron, chlorine

becomes a

negatively charged

ion.

Characteristics of ionic compounds

• Solid at room temperature

• Crystalline

• Do not conduct electricity as a solid

• Conduct electrical current in solution or

when molten

• High melting point

• Brittle

Ionic bonding and Structures of

Ionic Compounds

• Ions are packed together to maximize the

attractions between ions

Ionic bonding and Structures of

Ionic Compounds

• Cations are always

smaller than the

parent atom

• Anions are always

larger than the

parent atom

Example sodium and chlorine

• Sodium is a silver-colored metal that reacts so violently with water that flames are produced when sodium gets wet.

• Chlorine is a greenish-colored gas that is so poisonous that it was used as a weapon in World War I.

• When chemically bonded together, these two dangerous substances form the compound sodium chloride, a compound so safe that we eat it every day - common table salt!

Sodium and chlorine (continued)

+

Sodium

metal

chlorine

gas

table

salt

Salts

• Salts that are made of a simple cation and a simple

anion are known as binary ionic compounds.

• The adjective binary indicates that the compound

is made up of just two elements.

• All salts are electrically neutral ionic compounds

that are made up of cations and anions held

together by ionic bonds in a simple, whole-number

ratio.

Ionic Compounds are Salts

Writing the chemical formulas of

ionic compounds

• Monatomic ions

– Write the symbol for the cation (has a positive

charge) first.

– Write the symbol for anion (has a negative

charge) second.

– Use subscripts below each element symbol so

that the sum of the positive and negative

charges equal to zero.

Writing Ionic Compound Formulas

Example: Aluminum sulfide

1. Write the formulas for the

cation and anion, including

CHARGES!

2. Check to see if charges are

balanced.

3. Balance charges , if necessary,

using subscripts. (Use

parentheses if you need more

than one of a polyatomic ion.)

Al3+ S2-

Not balanced!

2 3

Now Balanced!

Chemical nomenclature

• A systematic method of naming compounds

according to IUPAC (International Union of Pure

and Applied Chemistry)

• There are three general types of compounds to

name, but the rules are generally the same.

– Ionic

– Covalent

– Organic

Naming Ionic Compounds

• The name of a binary ionic compound is made up of just two words: the name of the cation followed by the name of the anion.

NaCl sodium chloride CuCl2 copper(II) chloride

ZnS zinc sulfide Mg3N2 magnesium nitride

K2O potassium oxide Al2S3 aluminum sulfide

Rules of nomenclature

• Positive Ions

– Cations take the name of the element

• Example: Na+ = sodium ion

– If an element can form more than one (1) positive ion, the charge is indicated by Roman numeral in parentheses and named for the element

• Example: Fe2+ = iron(II)

• Example: Fe3+ = iron (III)

Nomenclature (continued)

• Negative Ions

– Anions (a single atom with a negative charge)

– change their ending to “-ide”

• Example: O2- = oxide

• Example: Cl- = chloride

– Polyatomic Ions (ions made up of more than

one atom that are covalently bonded, but have

an overall charge as a group) – simply name

the ion

• Example: CO32- = Carbonate

Ionic Bond Review

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