The Octet Rule Noble gases are unlike any other group of elements on the periodic table because of their extreme stability. Each noble gas has eight valence.

The Octet Rule Noble gases are unlike any other group of elements on the periodic table because of their extreme stability. Each noble gas has eight valence electrons, except for helium, which has two. The modern model of how atoms react to form compounds is based on the fact that the stability of a noble gas results from the arrangement of its valence electrons.

The Octet Rule The octet rule says that atoms can become stable by having eight electrons in their outer energy level, as shown in the noble gas, Neon, (or two electrons in the case of some of the smallest atoms).

The Octet Rule Elements become stable by achieving the same configuration of valence electrons as one of the noble gases, a noble gas configuration.

Forming Chemical Bonds
When energy is added to or taken away from a system, one phase can change into another. The force that holds two atoms together is called a chemical bond. Chemical bonds form because of attractions between oppositely charged atoms, called ions, or between electrons and nuclei.

Numbers in compounds In the formula for an ionic compound, the symbol of the cation is written before that of the anion. Subscripts, or small numbers written to the lower right of the chemical symbols, show the numbers of ions of each type present in a formula unit.

Electrons Can Be Transferred
Sodium is in Group IA or 1A or 1, so it has one valence electron. Na has one electron to lose to become like a noble gas in configuration. 1+ Chlorine is in Group VII or 7A or 17and has seven valence electrons. Cl has needs one electron to become like a noble gas in configuration.

How can the valence electrons of atoms rearrange to give each atom a stable configuration of valence electrons? If the one valence electron of sodium is transferred to the chlorine atom, chlorine becomes stable with an octet of electrons.

Because the chlorine atom now has an extra electron, it has a negative charge. Also, because sodium lost an electron, it now has an unbalanced proton in the nucleus and therefore has a positive charge.

Now that each atom has an octet of outer-level electrons, they are no longer neutral atoms; they are charged particles called ions. An ion is an atom or group of combined atoms that has a charge because of the loss or gain of electrons.

A compound that is composed of ions is called an ionic compound. Note that only the arrangement of electrons has changed. Nothing about the atom’s nucleus has changed. Na 1+ and Cl 1- Na1Cl1 NaCl

Formation of an Ionic Compound
Remember that objects with opposite charges attract each other. The strong attractive force between ions of opposite charge is called an ionic bond. The force of the ionic bond holds ions together in an ionic compound.

Unprotected aluminum metal reacts with oxygen in air, forming the white coating you can observe on aluminum objects such as lawn furniture. Explain the formation of an ionic compound from the elements aluminum and oxygen.

1. Analyze the Problem You are given that aluminum and oxygen react to form an ionic compound. Aluminum is a group 3A element with three valence electrons, and oxygen is a group 6A element with six valence electrons. To acquire a noble gas configuration, each aluminum atom must lose three electrons and each oxygen atom must gain two electrons.

2. Solve for the Unknown Remember that the number of electrons lost must equal the number of electrons gained. The smallest number evenly divisible by the three electrons lost by aluminum and the two gained by oxygen is six. Three oxygen atoms are needed to gain the six electrons lost by two aluminum atoms.

3. Evaluate the Answer The overall charge on one unit of this compound is zero.

Forming Chemical Bonds
A cation, or positive ion, is formed when an atom loses one or more electrons. An anion, or negative ion, is formed when an atom gains one or more electrons.

Determining Charges of Ions
To determine the electron configuration, refer to the periodic table. Write the formula of the ion the atom is most likely to form. Next, identify that ion as a cation or an anion.

Properties of ionic compounds and lattice energy
In a solid ionic compound, the positive ions are surrounded by negative ions, and the negative ions by positive ions. The resulting structure is called a crystal lattice and contains a regular, repeating, three-dimensional arrangement of ions.

The energy required to separate one mole of the ions of an ionic compound is called lattice energy, which is expressed as a negative quantity. The greater (that is, the more negative) the lattice energy is, the stronger is the force of attraction between the ions. Lattice energy tends to be greater for more-highly-charged ions and for small ions than for ions of lower charge or large size.

Based on the properties of the following “unknowns,” each is classified as either ionic or not ionic. Ionic Not Ionic has a high boiling point and shatters when hammered conducts electricity when liquid and has a low melting point has a high melting point and conducts electricity when dissolved in water conducts electricity when solid

Between each of the following pairs of ionic compounds, only one would be expected to have the higher (more negative) lattice energy. 1. LiF or KBr (LiF would have the higher lattice energy) Cinda, this is the way it was typed. The answers to each question are in the parentheses, so I don’t know if they are supposed to be a separate point or not. 2. NaCl or MgS (MgS would have the higher lattice energy)

Names and Formulas for Ionic Compounds
The simplest ratio of the ions represented in an ionic compound is called a formula unit. The overall charge of any formula unit is zero. In order to write a correct formula unit, one must know the charge of each ion.

The charges of monatomic ions, or ions containing only one atom, can often be determined by referring to the periodic table or table of common ions based on group number.

For example, ions of group 1A typically have a charge of 1+. Those of group 2A have a charge of 2+. Those of group 7A have a charge of 1–.

The charge of a monatomic ion is equal to its oxidation number. The oxidation number, or oxidation state, of an ion in an ionic compound is numerically equal to the number of electrons that were transferred to or from an atom of the element in forming the compound.

Naming ionic compounds
In naming ionic compounds, name the cation first, then the anion. Monatomic cations use the element name. Monatomic anions use the root of the element name plus the suffix -ide. If an element can have more than one oxidation number, use a Roman numeral in parentheses after the element name, for example, iron(II) to indicate the Fe2+ ion. For polyatomic ions, use the name of the ion.

Certain polyatomic ions, called oxyanions, contain oxygen and another element. If two different oxyanions can be formed by an element, the suffix -ate is used for the oxyanion containing more oxygen atoms, and the suffix -ite for the oxyanion containing fewer oxygens. In the case of the oxyanions of the halogens, the following special rules are used.

four oxygens, per + root + -ate (example: perchlorate, ClO4–) three oxygens, root + -ate (example: chlorate, ClO3–)

two oxygens, root + -ite (example: chlorite, ClO2–) one oxygen, hypo- + root + -ite (example: hypochlorite, ClO–)

The formulas below are followed by their ionic compound. 1. NaBrO (sodium bromate) 2. Mg(NO3)2 (magnesium nitrate) 3. NH4ClO (ammonium perchlorate) 4. Al(ClO) (aluminum hypochlorite)

Additional Assessment Questions
What structure has positive ions surrounded by negative ions, and the negative ions surrounded by positive ions? Answer a crystal lattice

What is the correct formula for the ionic compound aluminum sulfate? Answer Al2(SO4)3

Practice Problems Question 1 Determine the correct formula for the ionic compound composed of the following pairs of ions.

Question 1a Answer 1a aluminum and carbonate Al2(CO3)3
Practice Problems Question 1a aluminum and carbonate Answer 1a Al2(CO3)3

Practice Problems Question 1b magnesium and carbonate Answer 1b MgCO3

Practice Problems Question 1c calcium and chlorate Answer 1c Ca(ClO3)2

Practice Problems Question 2 Name the following compounds.

Practice Problems Question 2a Co(OH)2 Answer 2a cobalt hydroxide

Practice Problems Question 2b Ag2CrO4 Answer 2b silver chromate

Practice Problems Question 2c Na3PO4 Answer 2c sodium phosphate

Explaining the Properties of Ionic Compounds
Ionic compounds are composed of well-organized, tightly bound ions. These ions form a strong, three-dimensional crystal structure. Ionic compounds are crystalline solids at room temperature.

Explaining the Properties of Ionic Compounds
Ionic compounds usually have to be heated to high temperatures in order to melt them because the attractions between ions of opposite charge are strong.

Electrolytes Another physical property of ionic compounds is their tendency to dissolve in water and conduct electricity in the liquid (melted) state. Any compound that conducts electricity when melted or dissolved in water is an electrolyte. In order to conduct electricity, ions must be free to move because they must take on or give up electrons.

Question 1 Answer What is the difference between sodium and chlorine?
Basic Assessment Questions Question 1 What is the difference between sodium and chlorine? Answer Sodium is a metal that can be cut with a knife and has a silvery luster where it has been cut. Chlorine is a pale green, poisonous gas that kills living cells.

Ionic Compounds The submicroscopic structure of ionic compounds helps explain why they share certain macroscopic properties such as high melting points, brittleness, and the ability to conduct electricity when molten or when dissolved in water. You have learned that ionic compounds are made up of oppositely charged ions held together strongly in well-organized units.

Ionic Compounds Because of their structure, they usually are hard solids at room temperature and are difficult to melt. Look at the structure of magnesium oxide.

Ionic Compounds When ionic compounds melt or dissolve in water, their three-dimensional structure breaks apart, and the ions are released from the structure.

Ionic Compounds These charged ions are now free to move and can conduct an electrical current.

Binary Ionic Compounds
Formulas are part of the language that is used to communicate information about substances. As a first step in studying this new language, you will learn how to name and write formulas for ionic compounds.

Sodium chloride (NaCl) contains only sodium and chlorine, and potassium iodide (KI) contains only potassium and iodine. Each is an example of a binary compound, which is a compound that contains only two elements.

Binary ionic compounds can contain more than one ion of each element, as in CaF2, but they are not composed of three or more different elements, as are more complex compounds.

To name a binary ionic compound, first write the name of the positively charged ion, usually a metal, and then add the name of the nonmetal or negatively charged ion, whose name has been modified to end in -ide. The compound formed from potassium and chlorine is called potassium chloride. Magnesium combines with oxygen to form a compound called magnesium oxide.

You are already familiar with one formula for an ionic compound—NaCl. Sodium chloride contains sodium ions that have a 1+ charge and chloride ions that have a 1– charge. You have learned that compounds are electrically neutral.

This means that the sum of the charges in an ionic compound must always equal zero. Thus, one Na+ balances one Cl– in sodium chloride.

When you write a formula, you add subscripts to the symbols for the ions until the algebraic sum of the ions’ charges is zero. The smallest subscript to both ions that results in a total charge of zero is 1. However, no subscript needs to be written because it is understood that only one ion or atom of an element is present if there is no subscript.

The formula NaCl indicates that sodium chloride contains sodium and chloride ions, that there is one sodium ion present for every chloride ion in the compound, and that the compound has no overall charge.

If more than one ion of a given element is present in a compound, the subscript indicates how many ions are present. The mineral known as fluorite is calcium fluoride, which has the formula CaF2. This formula indicates that there is one calcium ion for every two fluoride ions in the compound.

In an ionic compound, a formula represents the smallest ratio of atoms or ions in the compound.

In a covalent compound, the smallest unit of the compound is a molecule, so a formula represents a single molecule of a compound. This simplest ratio of ions in a compound is called a formula unit. Each formula unit of calcium fluoride consists of one calcium ion and two fluoride ions. Each of the three ions has a stable octet configuration of electrons, and the formula unit has no overall charge.

Predicting Charge on Ions
The noble gases each have eight electrons in their outer-energy levels. Metals have few outer-level electrons so they tend to lose them and become positive ions. Sodium must lose just one electron, becoming an Na+ ion. Calcium must lose two electrons, becoming a Ca2+ ion.

Most nonmetals, on the other hand, have outer-energy levels that contain four to seven electrons, so they tend to gain electrons and become negative ions.

Because all elements in a given group have the same number of electrons in their outer-energy level, they must lose or gain the same number of electrons to achieve a noble-gas electron configuration. Metals always lose electrons and nonmetals always gain electrons when they form ions. The charge on the ion is known as the oxidation number of the atom.

The oxidation numbers for many elements in the main groups are arranged by group number.

Oxidation numbers for elements in Groups 3 through 12, the transition elements, cannot be predicted by group number.

Aluminum is in Group 13, so it loses its three outer electrons to become an Al3+ ion; oxygen is in Group 16 and has six valence electrons, so it gains two electrons to become an O2– ion.

Notice that one of aluminum’s three electrons has not been taken up by the oxygen atom. Because all the electrons must be accounted for, more than one oxygen atom must be involved in the reaction.

But, oxygen cannot gain only one electron, so a second aluminum atom must be present to contribute a second electron to oxygen. In all, two Al3+ ions must combine with three O2– ions to form Al2O3. Remember that the charges in the formula for aluminum oxide must add up to zero.

Compounds Containing Polyatomic Ions
The ions you have studied thus far have contained only one element. However, some ions contain more than one element. An ion that has two or more different elements is called a polyatomic ion. Although the individual atoms have no charge, the group as a whole has an overall charge.

Ionic compounds may contain positive metal ions bonded to negative polyatomic ions, such as in NaOH; negative nonmetal ions bonded to positive polyatomic ions, such as in NH4I; or positive polyatomic ions bonded to negative polyatomic ions, such as in NH4NO3.

To write the formula for an ionic compound containing one or more polyatomic ions, simply treat the polyatomic ion as if it were a single-element ion by keeping it together as a unit. Remember that the sum of the positive and negative charges must equal zero.

Multiples of a polyatomic ion in a formula can be indicated by placing the entire polyatomic ion, without the charge, in parentheses. Write a subscript outside the parentheses to show the number of polyatomic ions in the compound. Never change the subscripts within the polyatomic ion.

To do so would change the composition of the ion. The formula for the compound that contains one magnesium ion and two nitrate ions is Mg(NO3)2.

To name a compound containing a polyatomic ion, follow the same rules as used in naming binary compounds. Name the positive ion first, followed by the negative ion.

However, do not change the ending of the negative polyatomic ion name. The name of the compound composed of calcium and the carbonate ion is calcium carbonate.

Calcium is in Group 2, so its ion has a 2+ charge. The carbonate ion has a 2– charge. To form a neutral compound, one Ca2+ ion must combine with one CO32– ion to give the formula CaCO3.

Compounds of Transition Elements
Elements known as transition elements are located in Groups 3 through 12 in the periodic table. Transition elements form positive ions just as other metals do, but most transition elements can form more than one type of positive ion. In other words, transition elements can have more than one oxidation number.

For example, copper can form both Cu+ and Cu2+ ions, and iron can form both Fe2+ and Fe3+ ions. Zinc and silver are two exceptions to the variability of other transition elements; each forms one type of ion. The zinc ion is Zn2+ and the silver ion is Ag+.

Chemists must have a way to distinguish the names of compounds formed from the different ions of a transition element. They do this by using a Roman numeral to indicate the oxidation number of a transition element ion.

This Roman numeral is placed in parentheses after the name of the element. No additional naming system is needed for zinc and silver compounds because their formulas are not ambiguous.

Formation of Water by Electron Sharing
The stability of the atoms in a water molecule results from a cooperative arrangement in which the eight valence electrons (six from oxygen and one each from two hydrogens) are distributed among the three atoms.

By sharing an electron pair with the oxygen, each hydrogen claims two electrons in its outer level.

The oxygen, by sharing two electrons with two hydrogens, claims a stable octet in its outer level. By this method, each atom achieves a stable noble gas configuration.

Electron Sharing Produces Molecules
The attraction of two atoms for a shared pair of electrons is called a covalent bond. Notice that in a covalent bond, atoms share electrons and neither atom has an ionic charge.

A compound whose atoms are held together by covalent bonds is a covalent compound. Water is a covalent compound.

A molecule is an uncharged group of two or more atoms held together by covalent bonds. Ethanol, also known as ethyl alcohol, is a typical covalent compound.

Basic Assessment Questions
How many valence electrons must an atom have in its outer energy level in order to be considered stable? Answer The answer is 8.

Do atoms that share a covalent bond have an ionic charge? Answer No, the atoms share electrons and neither atom has a charge.

Question 4 Answer Name the following molecular compounds CO CO2 NO
Basic Assessment Questions Question 4 Name the following molecular compounds CO CO2 NO N2O3 Answer No, the atoms share electrons and neither atom has a charge.

Properties of Molecular Substances
You know that ionic compounds share many properties. The properties of a molecular substance—a substance that has atoms held together by covalent rather than ionic bonds—are more variable than the properties of ionic compounds.

Molecular substances usually have lower melting points, and most are not as hard as ionic compounds. In addition, most molecular substances are less soluble in water than ionic compounds and are not electrolytes.

A molecule that forms when atoms of the same element bond together is called a molecular element. Note that molecular elements are not compounds—they contain atoms of only one element.

When they bond together, each atom achieves the stability of a noble-gas electron configuration. Seven nonmetal elements are found naturally as molecular elements of two identical atoms.

The elements whose natural state is diatomic are: hydrogen, chlorine, nitrogen, bromine, oxygen, and iodine fluorine,

Their formulas can be written as: H2, Cl2, N2, Br2, O2, and I2, respectively F2, Mr. BrINClHOF or Special 7

If two chlorine atoms combine, they share a single pair of electrons, and each atom attains a stable octet configuration.

Two oxygen atoms share two pairs of electrons to form O2, and two nitrogen atoms share three pairs of electrons to form N2.

Formulas and Names of Molecular Compounds
Chemists have devised a naming system for molecular compounds that is based on a much smaller number of rules than there are compounds. Substances are either organic or inorganic. Compounds that contain carbon, with a few exceptions, are classified as organic compounds.

Formulas and Names of Molecular Compounds
Compounds that do not contain carbon are called inorganic compounds. To name these compounds, write out the name of the first nonmetal and follow it by the name of the second nonmetal with its ending changed to -ide.

Determine the ratio of the atoms in the ionic compound formed in each case. A. aluminum (Al) and fluorine (F) B. lithium (Li) and oxygen (O)

Answers A. aluminum (Al) and fluorine (F) one AL for every three F
Basic Assessment Questions Answers A. aluminum (Al) and fluorine (F) one AL for every three F B. lithium (Li) and oxygen (O) two Li for every O

Write the correct formula for the ionic compound formed between atoms of each of the following pairs of elements. A. sodium (Na) and sulfur (S) B. magnesium (Mg) and nitrogen (N)

Answers A. sodium (Na) and sulfur (S) Na2S
Basic Assessment Questions Answers A. sodium (Na) and sulfur (S) Na2S B. magnesium (Mg) and nitrogen (N) Mg3N2

For each of the following atoms, write the formula of the ion the atom is most likely to form and identify that ion as a cation or an anion. A. bromine (Br), element 35 B. gallium (Ga), element 31

Answers A. bromine (Br), element 35 Br– anion
Additional Assessment Questions Answers A. bromine (Br), element 35 Br– anion B. gallium (Ga), element 31 Ga3 cation

Question 2 Name the ionic Compounds that have the following formulas.
Additional Assessment Questions Question 2 Name the ionic Compounds that have the following formulas. A. Mg(NO3)2 B. KHSO4

Answers A. Mg(NO3)2 magnesium nitrate B. KHSO4
Additional Assessment Questions Answers A. Mg(NO3)2 magnesium nitrate B. KHSO4 potassium hydrogen sulfate

The Octet Rule Noble gases are unlike any other group of elements on the periodic table because of their extreme stability. Each noble gas has eight valence.

Similar presentations

Presentation on theme: "The Octet Rule Noble gases are unlike any other group of elements on the periodic table because of their extreme stability. Each noble gas has eight valence."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

The Octet Rule Noble gases are unlike any other group of elements on the periodic table because of their extreme stability. Each noble gas has eight valence.

Similar presentations

Presentation on theme: "The Octet Rule Noble gases are unlike any other group of elements on the periodic table because of their extreme stability. Each noble gas has eight valence."— Presentation transcript:

Similar presentations

About project

Feedback