CS_Ch7_PeriodicTbl 4/27/06 1:45 PM Page 442 The Periodic Table Activity 8 How Atoms Interact with Each Other GOALS What Do You Think? In this activity you will: You have learned that the chemical behavior of an atom is • Relate patterns in ionization determined by the arrangement of the atom’s electrons, energies of elements to specifically the valence electrons. The salt that you put on patterns in electron your food is chemically referred to as NaCl—sodium chloride. arrangements. • Use your knowledge of • How might the valence electrons of sodium (Na) and electron arrangements and chlorine (Cl) interact to create this bond? valence electrons to predict formulas for compounds Record your ideas about this question in your Active formed by two elements. Chemistry log. Be prepared to discuss your responses with • Contrast ionic bonding and your small group and the class. covalent bonding. • Draw electron-dot diagrams Investigate for simple molecules with 1. In Activity 3 you read that John Dalton assumed that covalent bonding. chemical compounds formed from two elements combined in the simplest possible combination—one atom of each element. In Activity 6 you began to see that an atom’s chemical behavior reflects its excess or deficiency of electrons relative to an atom of the closest noble gas on the periodic table. Use the list of ionization energies in Activity 6 to answer the following questions: 442 Active Chemistry CS_Ch7_PeriodicTbl 2/28/05 10:04 AM Page 443 Activity 8 How Atoms Interact with Each Other a) Which atoms have the smallest stable electron arrangement as neon. values for first ionization energies? What is the electric charge on the (Remember, the first ionization resulting Na ion? energy is the amount of energy Consider a chlorine atom. required to remove the first electron.) a) How many valence electrons does a chlorine atom have? Where are these atoms located on the periodic table? b) How many electrons does a chlorine atom need to gain to have b) What do you observe about the the same number of electrons as an amount of energy required to argon atom? remove the second electron from atoms of the elements identified c) When a chlorine atom gains an in (a) above? electron, a chloride ion is formed. Since the original chlorine atom c) Use your understanding of the was electrically neutral and it arrangement of electrons in this gained a negative electron to form group of elements to suggest a the ion, what is the electric charge reason for the pattern you noted (sign and value) on the resulting in (b). ion? d) Which atoms have the smallest d) Each chlorine atom is capable of values for second ionization accepting one electron. Describe energies? Where are these atoms how you think the compound located on the periodic table? sodium chloride (NaCl) is formed? e) Use your understanding of the 3. Consider the reaction between arrangement of electrons in this aluminum and zinc chloride (similar group of elements to suggest a to the reaction in Activity 3). The zinc reason for the pattern you noted atoms in zinc chloride have two in (d). valence electrons located in the 2. Once you recognize the role of an 4s sublevel. You can note the two atom’s electron arrangement— valence electrons in the electron especially the valence electrons—in an arrangement marked on the atom’s chemical activity, you can periodic table. often predict formulas for compounds In order to acquire the electron formed by two chemical elements. configuration of argon atoms a rather (Recall that valence electrons are the stable arrangement, the zinc atoms electrons located in the highest energy give up their two valence electrons to level, the levels designated by the form zinc ions. Since the original zinc sublevel having the highest numbers.) atom was electrically neutral and it Sodium (Na) has one valence electron lost two negative electrons to form in the 3s sublevel. By losing that the ion, the resulting ion has a electron, the sodium atom becomes a positive charge with a magnitude two sodium ion and it has the same times the charge on the electron. It has a plus two charge. 443 Coordinated Science for the 21st Century CS_Ch7_PeriodicTbl 2/28/05 10:04 AM Page 444 The Periodic Table a) Each chlorine atom is capable of a) Consider an atom of aluminum. accepting one electron. How many How many valence electrons does chlorine atoms are needed to an aluminum atom have? accept the 2 electrons that zinc b) How many electrons does an atoms have to give? aluminum atom need to give up to b) When writing the formula for a reach the same chemical stability compound, the number of atoms as a neon atom? necessary to balance the loss and c) What are aluminum atoms called gain of electrons can be designated after they give up their valence through the use of a subscript, electrons? What is their electric such as the 2 in H O. How would 2 charge (sign and value)? you write the formula for the compound zinc chloride? d) How many chlorine atoms are needed to accept the electrons 4. In a reaction between aluminum and given up by an aluminum atom? zinc chloride, aluminum replaces the zinc in the zinc chloride, forming e) How would you write the formula aluminum chloride and zinc. for the compound aluminum chloride? FORMING COMPOUNDS The Octet Rule Chem Words In this activity, you explained the formation of the compounds that halogens: group VIIA (17) you investigated by how the electrons are transferred or shared on the periodic table consisting of fluorine, between atoms. Some scientists explain these observations using the chlorine, bromine, iodine, octet rule. The octet rule works well with the representative and astatine. elements and is stated as follows: atoms tend to gain or lose binary compound: a compound, formed from electrons during chemical reactions so that the atoms have an outer the combining of two shell configuration of 8 electrons.The exceptions to this are the different elements. transition elements.They can form compounds that do not have 8 ionic bond: the attraction electrons in their outer shell. For example, when chlorine, one of the between oppositely charged ions. halogens (Group 17), gains one electron it now has 8 electrons in covalent bond: when two its outermost s and p sublevels (octet of electrons).Also, you should atoms combine and share note that the name of all of the compounds that you have studied their paired electrons with each other. always started with the name of the metal and then followed with the nonmetal part.The second thing that you should note is that all of these compounds are binary (meaning two parts). Binary compounds always end with the suffix ide (except for a few compounds with common names like water and ammonia). 444 Active Chemistry CS_Ch7_PeriodicTbl 2/28/05 10:04 AM Page 445 Activity 8 How Atoms Interact with Each Other Covalent and Ionic Bonds Checking Up You may have noticed that the column 1. When naming a headed by carbon in the periodic table binary compound, has not received a lot of attention so which element is named first, the far. In Activity 7 you learned that metal or the atoms of these elements contain 4 nonmetal? Give an valence electrons.Atoms with a small number of valence electrons give example to explain up electrons, and atoms with a large number of valence electrons gain your answer. additional electrons to have the same electron arrangement as an atom 2. Explain the difference between an ionic of the nearest noble gas. Except for helium, with 2 valence electrons, and a covalent bond. the noble gases each have 8 valence electrons.What do atoms of 3. Draw electron-dot carbon do: give up their 4 valence electrons, or gain 4 more? diagrams showing covalent bonding in In actuality, atoms of carbon do neither. Instead of giving or taking the following electrons, carbon atoms share electrons with atoms of other elements. compounds: Instead of giving or taking electrons to form what are called ionic a) water (two atoms bonds, carbon atoms share electrons with atoms of other elements to of hydrogen, one form what are called covalent bonds. In fact, all nonmetallic elements atom of oxygen). Note: Since the whose atoms have four or more valence electrons can form covalent noble gas nearest bonds by sharing electrons.This sharing results in a situation in which hydrogen is each atom is associated with 8 valence electrons, as is characteristic of helium, with only two valence an atom of a noble gas. electrons, Covalent bonding can be illustrated using electron-dot diagrams, in hydrogen atoms need be which each valence electron is indicated by a dot (or other appropriate associated with symbol) around the chemical symbol for the element in question. only two valence Consider the following covalent compound illustrations: electrons. b) methane (four hydrogen chloride water contains 2 and carbon dioxide atoms of contains one hydrogen hydrogen atoms and contains one atom of hydrogen, one atom and one atom of one oxygen atom: carbon and 2 oxygen atom of carbon). chlorine: atoms: c) ammonia (three H O atoms of H Cl O C O hydrogen, one H atom of nitrogen). d) carbon You can count 8 electrons around the chlorine in hydrogen chloride tetrachloride (four (note that hydrogen can only have 2 electrons). In water the oxygen atoms of chlorine, has 8 electrons around it and hydrogen again has only 2 electrons. one atom of Carbon dioxide shows that oxygen contains 8 electrons and carbon carbon).