1. Chapter 7 Ionic and Metallic Bonding

2. valence Electrons
Scientists learned that all of the elements within each group of the periodic table behave similarly because they have the same number of valence electrons.
valence electrons are the electrons in the highest occupied energy level of an element’s atom.
The number of valence electrons largely determines the chemical properties of an element.
To find the number of valence electrons in an atom of a representative elements, simply look at its group number
Elements of Group IA have one valence electron. Elements in Group 4A have four valence electrons, and so forth

3. valence Electrons
The noble gases, Group 8A, are the only exceptions to the group-number rule.
Helium has two valence electrons, and all of the other noble gases have eight.
valence electrons are usually the only electrons used in chemical bonds.
As a general rule, only the valence electrons are shown in electron dot structures.
Electron dot structures are diagrams that show valence electrons as dots.

4. Electron Dot Structures

5. The Octet Rule
Noble gases, such as neon and argon, are unreactive in chemical reactions. (They are stable)
Gilbert Lewis explained why atoms form certain kinds of ions and molecules in the octet rule
The Octet Rule - in forming compounds, atoms tend to achieve the electron configuration of a noble gas. An octet is a set of eight. (each noble gas except helium has eight electrons in its highest energy level)
Atoms of the metallic elements tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level. Atoms of some nonmetallic elements tend to gain electron or to share electrons with another nonmetallic element to achieve a complete octet.

6. Formation of Cations
An atom is electrically neutral because it has equal numbers of protons and electrons; an ion forms when an atoms or group of atoms loses or gains electrons.
An atom’s loss of valence electrons produced a cation, or a positively charged ion.
For metallic elements, the name of the ion is the same as the name of the element.
Although their names are the same, there are many important chemical differences between metals and their cations.

7. Formation of Cations
An atom is electrically neutral because it has equal numbers of protons and electrons; an ion forms when an atoms or group of atoms loses or gains electrons.
An atom’s loss of valence electrons produced a cation, or a positively charged ion.
For metallic elements, the name of the ion is the same as the name of the element.
Although their names are the same, there are many important chemical differences between metals and their cations.

8. Formation of Cations ·Mg· Mg2+ + 2e-
Using electron dot structures, you can show the ionization of some elements more simply.
Na· Na e-
Sodium atom Sodium ion electron
neutral unit of + charge unit of - charge
·Mg· Mg e-
Magnesium atom Magnesium ion electron
neutral unit of + charge units of - charge

9. Transition Metals
For transition metals, the charges of cations may vary.
An atom of iron (Fe) may lose two, or three electrons forming either Fe2+ or Fe3+ ions.
Some ions formed by transition metals do not have noble gas electron configurations and are therefore exceptions to the octet rule.
Ag is an example - 1s22s22p63s23p63d104s24p64d105s1
To achieve the structure of krypton, which is the preceding noble gas, a silver atom would have to lose eleven electrons.

10. Transition Metals
Ions with charges of three or greater are uncommon, and losing eleven electrons is highly unlikely.
If Ag loses its 5s1 electron, the configuration that results, (4s24p64d10) with 18 electrons in the outer energy level and all of the orbitals filled, is relatively favorable in compounds.
Such a configuration is known as pseudo noble-gas electron configuration.
Ag forms a positive ion (Ag+) in this way.

11. Formation of Anions
The gain of negatively charge electrons by a neutral atom produces an anion.
The name of an anion of a nonmetallic element is not the same as the element name. The name of the ion typically ends in -ide.
Chlorine atom (Cl) forms a chloride ion (Cl-)
Oxygen atom (O) forms an oxide ion (O2-)
Because they have relatively full valence shells, atoms of nonmetallic elements attain noble-gas electron configurations more easily by gaining electrons than by losing them.

12. Formation of Anions
Chlorine belongs to Group 7A and has seven valence electrons. A gain of one electron gives chlorine an octet and converts a chlorine atom into a chloride ion.
Atoms of nonmetallic elements form anions by gaining enough valence electrons so as to attain the electron configuration of the nearest noble gas.
The chloride ion has the same electron configuration as the noble gas argon.
Chloride ion (Cl-) 1s22s22p63s23p6
Argon (Ar) 1s22s22p63s23p6

13. Food For Thought
Chlorine atoms need one more valence electron to achieve the electron configuration of the nearest noble gas.
Any electron in an atom outside the noble gas core is called a valence electron.
Various atoms of the representative elements form ions and gain a noble-gas electron configuration

14. Formation of Anions
Halide ions – the ions that are produced when atom of chlorine and other halogens gain electrons
All halogen atoms have seven valence electrons and need to gain only one electron to achieve the electron configuration of a noble gas.
All halide ions (F-, Cl-, Br-, and I-) have charge of 1-.

15. Questions
How can you determine the number of valence electrons in an atom of a representative element?
Look up the group number of that element
Atoms of which elements tend to gain electrons? Atoms of which elements tend to lose electrons?
Nonmetallic – gain metallic - lose
How do cations form? How do anions form?
Cation – atom loses valence electrons Anion – atom gains valence electrons

16. End of Section 7.1

17. Formation of Ionic Compounds
Compounds composed of cations and anions are called ionic compounds.
Ionic compounds are usually composed of metal cations and nonmetal anions. Ex: NaCl is formed from Na+ + Cl-
Although they are composed of ions, ionic compounds are electrically neutral. The total + charge of the cations equals the total – charge of the anions.
Anions and cations have opposite charges and attract one another by means of electrostatic forces.
The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.

18. Formation of Ionic Compounds
Compounds composed of cations and anions are called ionic compounds.
Ionic compounds are usually composed of metal cations and nonmetal anions. Ex: NaCl is formed from Na+ + Cl-
Although they are composed of ions, ionic compounds are electrically neutral. The total + charge of the cations equals the total – charge of the anions.
Anions and cations have opposite charges and attract one another by means of electrostatic forces.
The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.

19. Formation of Ionic Compounds
Look at the reaction of a Na atom and a chlorine atom.
Na has 1 valence electron that it can easily lose. (Na is in group 1A of the representative elements, thus has 1 valence electron)
Cl has seven valence electrons and can easily gain one electron. (Cl is in group 7A of the representative elements, thus has 7 valence electrons)
If Na loses its valence electron it achieves the stable electron configuration of neon. If Cl gains a valence electron, it achieves the stable electron configuration of argon. (Remember the Octet Rule)

20. Formation of Ionic Compounds
When Na and Cl react, the Na atom gives its one valence electron to a Cl atom. They react in a 1:1 ratio and both ions have stable octets. +
Na Cl-
1s22s22p s22s22p63s23p6

21. Formula Units
Chemists represent the composition of substances by writing chemical formulas. A chemical formula shows the kinds and numbers of atoms in the smallest representative unit of a substance.
NaCl is the chemical formula for sodium chloride.
A Formula unit is the lowest whole-number ratio of ions in an ionic compound. One Na+ to each Cl-, thus the formula unit for sodium chloride is NaCl.
Even though ionic charges are used to derive the correct formulas, they are not shown when you write the formula unit of the compound

22. Formula Units
The ionic compound Magnesium chloride (MgCl2) contains magnesium cations (Mg2+) and chloride anions (Cl-)
In MgCl2, the ratios of Mg2+ to Cl- is 1:2 (One Mg2+ to two Cl-). Its formula unit is MgCl2
Because there are twice as many Cl- (each with a 1- charge) as Mg2+ (each with a 2+ charge), the compound is electrically neutral.
Another example: Al3+ + Br- combine to form AlBr3.

23. Questions
Use electron dot structures to determine formulas of the ionic compounds formed when
Potassium reacts with iodine KI
Aluminum reacts with oxygen
Al2O3

24. Properties of Ionic Compounds
Most ionic compounds are crystalline solids at room temperature.
The component ions in such crystals are arranged in repeating three-dimensional patterns.
In NaCl, each sodium ion is surrounded by six chloride ions, and each chloride ion is surrounded by six sodium ions.
In this arrangement, each ion is attracted strongly to each of its neighbors and repulsions are minimized.
The large attractive forces result in a very stable structure.

25. Properties of Ionic Compounds
Ionic compounds can conduct an electric current when melted or dissolved in water.
When NaCl is melted, the orderly crystal structure breaks down.
The movement of the ions allows electricity to flow

26. Questions
How can you describe the electrical charge of an ionic compound?
Electrically neutral
What properties characterize ionic compounds?
Usually solids at room temperature; have high melting points; conduct electric current when melted or dissolved in water.
Define an ionic bond
Electrostatic forces that hold ions together in an ionic compound

27. Questions
Write the correct chemical formula for the compounds formed from each pair of ions.
K+ , S2- Ca2+ , O2-
Na+ , O2- Al3+ , N3-
K2S , CaO, Na2O , AlN
Write formulas for each compound: barium chloride, magnesium oxide, lithium oxide, calcium fluoride
BaCl2 MgO Li2O CaF2
Which pairs of elements are likely for form ionic compounds?
Cl, Br Li, Cl K, He I, Na
Li, Cl I, Na

28. End of Section 7.2

29. Metallic Bonds & Properties
Metals are made up of closely packed cations rather than neutral atoms.
The valence electrons of metal atoms can be modeled as a sea of electrons. (they are mobile and can drift freely from one part of the metal to another).
Metallic bonds consists of the attraction of the free-floating valence electrons from the positively charged metal ion.
The sea-of-electrons model explains many physical properties of metals.
Good conductors of electrical current because electrons can flow freely.
Ductile – they can be drawn into wires.
Malleable – they can be hammered or forced into shapes.

30. Crystalline Structure of Metals
The crystalline structures of metals
can be compared to the stacking of
oranges in the grocery store to save
space.
Metals are crystalline and they are
arranged in very compact and orderly
patterns.

31. Crystalline Structure of Metals
There are several closely packed arrangements that are possible.
body-centered cubic arrangement
face-centered cubic arrangement
hexagonal close-packed arrangement
Body-centered cubic
Every atom (except those on the
Surface) has eight neighbors.

32. Crystalline Structure of Metals
Face-centered cubic arrangement
every atom has twelve neighbors.

33. Crystalline Structure of Metals
Hexagonal close-packed arrangement
every atom also have twelve neighbors. Because of the hexagonal shape, the pattern is different from the face- centered.

34. Alloys
Very few of the metallic items that you use every day are pure metals. Ex: spoons.
Most of the metals you encounter are alloys.
Alloys are mixtures composed of two or more elements., at least on of which is a metal. Ex: Brass (Cu & Zn)
Alloys properties are often superior to those of their component elements.
Sterling silver (92.5% silver & 7.5% copper) is harder and more durable than pure silver, but still soft enough to be made into jewelry and tableware.

35. Alloys
Bronze – 7 parts copper to 1 part tin. Bronze is harder than copper and more easily cast.
Nonferrous (non-iron) alloys are commonly used to make coins.
The most important alloys today are steels.
Alloys can form from their component atoms in different ways. If the atoms of the components in an alloy are about the same size, they can replace each other n the crystal. (substantial alloy)
If the atomic sizes are different, the smaller atoms can fit into the spaces between the larger atoms. (interstitial alloy)

36. Questions How do chemists model the valence electrons in metal atoms?
Metal cations surrounded by a sea of mobile valence electrons.
How can you describe the arrangement of atoms in metals?
Atoms in metals are arranged in a compact and orderly manner
Why are alloys more useful than pure metals?
Their properties are often superior to their component elements.

37. End of Chapter 7