4.1 Chemical Bonds: attraction force between 2 atoms

Ionic Compounds - tend to have high melting points (500°C-2000°C) and are good

conductors of electricity when they are in a molten (liquid) state or solution. Unlike molecular compounds, they do not have molecules as their basic structural unit.

Instead there are an extended array of positively and negatively charged particles

called ions present.

○

Molecular Compounds - generally have much lower melting points and tend to be

gases, liquids, or low-melting solids. They do not conduct electricity in the molten states.

○

Chemical compounds are divided into two broad classes: Ionic Compounds, and Molecular

compounds which can be distinguished from each other on the basis of general physical properties

Chemical Bond - is the attractive for that holds two atoms together in a more complex

unit. They form as a result of interactions between electrons found in the combining atoms. The nature of chemical bonds are linked to electron configuration.

Ionic Bond - is a chemical bond formed through the transfer of one or more electrons

from one atom or group of atoms to another atom or group of atoms.

Ionic Compound - is a compound in which ionic bonds are present.

Covalent Bond - a chemical bond formed through the sharing of one or more pairs of

electrons between two atoms

Molecular Compound - is a compound in which atoms are joined through covalent bonds.

Most bonds aren't 100% ionic or 100% covalent. Most bonds have some degree of both

ionic and covalent character; some of both the transfer and the sharing electrons.

4.2 Valence Electrons and Lewis Symbols

Valence electron - is an electron in the outermost electron shell of a representative

element of noble-gas element.

12Mg = 1s22s22p63s2 Number of valence electrons (2). Mg is in Group 2, Period 3

Highest value of the electron

shell number (3)

Examples:

shell number is n=3, and there are only 2 electrons found in

shell 3

CH 4 - Chemical Bonding: The Ionic Bond ModelThursday, September 20, 200711:26 PM

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Both number 3's are in the outermost shell14Si = 1s22s22p63s23p2 Number of valence electrons (4)

Si is in Group IVA and in Period 3 get 4.

and we just add their electrons together to

33As = 1s22s22p63s23p64s23d104p3 There are 5 electrons in this example in the

As in Group VA and in Period 4 4th outermost shell

Group number indicates the number of valences

Lewis Symbol - is the chemical symbol of an element surrounded by dots equal in

number to the number of valence electrons present in atoms of the element.

The general practice in writing Lewis symbols is to place the first four "dots" separate on

the four sides of the chemical symbol and then begin pairing the dots as further dots are added.

Representative Elements in the same group of the periodic table have the same

number of valence electrons

1.

The number of valence electrons for representative elements is the same as the

Roman numeral periodic-table group number

2.

The maximum number of valence electrons for any element is eight3.

Generalizations About Valence Electrons

Example:

= 6 Valence ElectronsAdd the electrons in the outermost shell 4+2=6

Sulfur = 16S = 1s22s22p63s23p4

Octet Rule - In forming compounds, atoms of elements lose, gain, or share electrons in

such a way as to produce a noble-gas electron configuration for each of the atoms involved. This rule doesn't apply to Group 1B-7B

The valence electron configuration of noble gases (helium, neon, argon, krypton, xenon,

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The valence electron configuration of noble gases (helium, neon, argon, krypton, xenon,

and radon) are considered the moststable of all valence electron configurations. All noble gases except helium posses eight valence electrons, which is the maximum

number possible.

2He: 1s2

10Ne: 1s22s22p6

18Ar: 1s22s22p63s23p6

36Kr: 1s22s22p63s23p64s23d104p6

54Xe: 1s22s22p63s23p64s23d104p65s24d105p6

86Rn: 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106d6

Noble Gas Notation

10Ne [He] 2s22p6

= 1s22s22p6

Other elements can gain this configuration

by gaining or losing an electron

ns2np6 = noble gas, where n equals the shell number

He = 1s2

4.4 Ionic Bond Model

The electron transfer process produces charged particles called ions.

Ion - is an atom (or group of atoms) that is electrically charged as a result of the loss or

gain of electrons.

An atom is neutral when the number of protons (+ charges) is equal to the number of

electrons (- charges). Loss or gain of electrons destroys this proton-electron balance and leaves a net charge on the atom.

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If an atoms gains one or more electrons, it becomes a negatively charged ion; excess

negative charge is present because electrons outnumber protons.

If an atom loses one or more electrons, it becomes a positively charged ion; more

protons are present than electrons and there is a positive charge.

The charge of an ion depends on the number of electrons that are lost or gained.

A loss of one, two, or three electrons gives ions with +1, +2, or +3 charges

A gain of one, two, or three electrons gives ions with -1, -2, or -3 charges

Positive Ions: Na+, K+

Negative Ions: Cl-, Br-

Ex 1:

The ion formed when a barium atom loses two electrons:

56 protons = 56 + charges54 electrons = 54 - charges

56-54=2 Net Charge = 2+, thus the symbol of barium ion is Ba2+

A neutral barium atom contains 56 protons and 56 electrons because barium

has an atomic number of 56. The barium ion formed by the loss of 2 electrons would still contain 56 protons but would have only 54 electrons

because 2 electrons were lost.

The ion formed when a phosphorus atom gains three electrons:

15 protons = 15 + charges

18 electrons = 18 - charges15-18=-3

Net Charge = 3-, thus the symbol for the ion is P3-

The atomic number of phosphorus is 15. thus 15 protons and 15 electrons

are present in a neutral phosphorus atom. A gain of 3 electrons raises the electron count to 18.

Ex 2:

The notation for charges on ion is a superscripts placed to the right of the chemical

symbol.

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4.5 The Sign and Magnitude of Ionic Charge

Atoms tend to gain or lose electrons until they have obtained an electron configuration

that is the same as that of noble gas.

Ex: Sodium = 1s22s22p63s1

One valence electron is present. Sodium can attain a noble-gas electron configuration

by losing this valence electron (to give it the electron configuration of neon) or by gaining seven electrons (to give it the electron configuration of argon)

Na ( 1s22s22p63s1) Loss of 1 e- = Na+ ( 1s22s22p6 ) Electron configuration of neon

Gain of 7 e- = Na7- ( 1s22s22p63s23p6 ) Electron configuration of

argon.

Na+ is the preferred configuration = cation

Cl ( 1s22s22p63s23p5 ) Loss of 7 e- = Cl7+ ( 1s22s22p6 ) Electron configuration of

Gain on 1 e- = Cl- ( 1s22s22p6 3s23p6 ) Electron configuration

Cl- is the preferred configuration = ion of argon.

neon.

A + charge = cationA - charge = ion

From an energy standpoint, the electron loss or gain that involves the fewest

electrons will always be the more favorable process

Generalizations:

Group IA metals form 1+ ions

Group IIA metals form 2+ ionsGroup IIIA metals form 3+ ions

Metal atoms that contain one, two, or three valence electrons tend to lose

electrons to acquire a noble-gas electron configuration.

1.

Group VIIA nonmetals form 1- ions

Group VIA nonmetals form 2- ionsGroup VA nonmetals form 3- ions

Nonmetal atoms containing five, six, or seven valence electrons tend to gain

electrons to acquire a noble-gas electron configuration

2.

Elements in Group IVA occupy unique positions relative to the noble gases. They

would have to gain or lose four electrons to attain a noble-gas structure. Ions with charges of +4 or -4 could be formed in this group, but in most cases these

elements form covalent bonds instead

3.

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4.6 Ionic Compound Formation: when the positive and negative ions attract one another

and form an electron transfer

Electron loss and electron gain are always partner processes; if one occurs, the other also

occurs.

Ion formation requires the presence of two elements, a metal that can donate electrons

and a nonmetal that can accept electrons.

The electrons lost by the metal are the same ones gained by the nonmetal.

Lewis structure - is a combination of Lewis symbols that represents either the transfer or

the sharing of electron in chemical bonds. Lewis structures are helpful in visualizing the formation of simple ionic compounds. These structures involve individual elements;

involve compounds.

******see examples on back of page

4.7 Chemical Formulas for Ionic Compounds

Electron loss always equals electron gain in electron transfer process. Ionic compounds

are always neutral.

Ex: The correct combining ration when K+ ions and S2- ions combine is two to one.

Two K+ ions (each of +1 charge) are required to balance the charge on a single S2-

ion.

2(K+): (2 ions) x (charge of +1) = +2

Net Charge = 0

S-: (1 ion) x (charge of -2) = - 2

The formula of the compound formed is K2S

The symbol for the positive ion is always written first1.

The charges on the ions that are present are not shown in the formula. You need

to know the charges to determine the formula; however, the charge s are not explicitly shown in the formula.

2.

The numbers in the formula (the subscripts) give the combining ration for the

ions.

3.

Rules:

Ions are combined in the ratio that causes the positive and negative charge to add to zero

Formula Unit: the smallest whole-number repeating ratio of ions present in an ionic

compound that results in charge neutrality.

Binary Compound - is a compound in which only two elements are present. Ex's: NaCl

and, CO2

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Ex: NaF = Sodium Fluoride

Rule: the full name of the metallic element is given first, followed by a separate word

containing the stem of nonmetallic element name and the suffix -ide

Binary Ionic Compound - is an ionic compound in which one element present is a metal

and the other element present is a nonmetal. The metal is always present as the positive ion and the nonmetal is always present as the negative ion.

4.10 Polyatomic Ions

Monoatomic ion - is an ion formed from a single atom through loss or gain of

electrons.Polyatomic ion - is an ion formed from a group of atoms (held together by covalent

bonds) through loss or gain of electrons

Two categories of ions: monoatomic and polyatomic

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