CHEM Review Chap 7: Ionic Compounds & Metals

Write electron (Lewis) dot structures for ionic compounds.

The dots are placed in four groups of one or two electrons each, with 8 electrons representing a closed shell or noble gas configuration. Lewis diagrams are useful for visualizing both ionic and covalent bonds. In the idealized ionic bond, one atom gives up an electron to the other, forming positive and negative ions.

Determine the ionic charges of representative elements.

There is a quick way to work out what the charge on an ion should be: The number of charges on an ion formed by a metal is equal to the group number of the metal. The number of charges on an ion formed by a non-metal is equal to the group number minus eight. Hydrogen forms H+ ions.

Use the periodic table and table of common ions to name ionic compounds.

Write down the formula of the ionic compound. Write the name of the metal, or the cation. This is the positively charged ion in the compound, and it is always written first in ionic compound formulas. Write the name of the nonmetal, or the anion, with the "-ide" ending. Combine the names.

Describe the sea of electrons.

a model of metallic bonding in which cations are considered to be fixed points within a mobile 'sea' of electrons. Bonding in metals, called metallic bonding, involves valence electrons. These electrons are loosely held by any one atom and collectively form a "sea of valence electrons" that can be used to explain many metallic properties, e.g., metallic luster, malleability, electrical conductivity, etc.

Use the periodic table and table of common ions to write the formulas for ionic compounds.

i. Write the symbols for the ions and their charges ii. Determine how many of each ion you need to make their charges equal out (hint; if you use the absolute value of the charge of one ion as the subscript for the other, it usually works out) iii. Use subscripts to indicate how many ions are needed. iv. Write the final formula without the charges, but with the subscripts

Explain what is meant by unit cell.

A unit cell is the building block of a crystal or we can say it is the simplest repeating unit of a crystal lattice.unit cell when arranged in 3 dimensional pattern is known as crystal lattice

Explain the octet rule.

The Octet rule is a general rule of thumb that applies to most atoms. Basically, it states that every atom wants to have eight valence electrons in its outermost electron shell, giving it the same electron configuration as a noble gas

Describe and give examples of alloys

An alloy is a mixture of two elements, one of which is a metal. Alloys often have properties that are different to the metals they contain. This makes them more useful than the pure metals alone. For example, alloys are often harder than the metal they contain. Some familiar examples of alloys include brass, bronze, pewter, cast and wrought iron, steel, coin metals, and solder (pronounced SOD-der; a substance used to join other metallic surfaces together).

Define ductility related to metals.

Ductility is when a solid material stretches under tensile stress. If ductile, a material may be stretched into a wire. Malleability, a similar property, is a material's ability to deform under pressure (compressive stress). If malleable, a material may be flattened by hammering or rolling.

Explain why ionic compounds are in the smallest whole number ratio.

Empirical formula shows the smallest whole-number ratios of the different atoms in a compound, but does not necessarily indicate the actual number of atoms present in each molecule.

Describe the properties of ionic compounds.

High melting and boiling points - Ionic bonds are very strong - a lot of energy is needed to break them. So ionic compounds have high melting and boiling points. Conductive when liquid - Ions are charged particles, but ionic compounds can only conduct electricity if their ions are free to move. Ionic compounds do not conduct electricity when they are solid - only when dissolved in water or melted.

Define heat and electrical conductivity related to metals.

In metals, some electrons (often one per atom) are not stuck to individual atoms but flow freely. Of course, that's why metals are such good conductors of electricity. Now if one end of a bar is hot, and the other is cold, the electrons on the hot end have a little more thermal energy- random jiggling- than the ones on the cold end. So as the electrons wander around, they carry energy from the hot end to the cold end, which is another way of saying they conduct heat. How fast they conduct heat depends on how many free electrons are around, how fast they move, and how far they go before they bump into something and change direction. Those are the same factors that determine how well the metal conducts electricity. Electrons can can flow right through a perfect crystal without bouncing, the same way light travels through a clear crystal. Lots of metals are alloys of several elements, and the electrons bounce off all the irregularities in the arrangement of the different atoms. So those aren't good conductors. Even in a pure metal, the electrons still bounce some, because the thermal jiggling of the atoms keeps them from ever forming a perfectly exact crystal arrangement.

Describe a crystal lattice.

In most ionic compounds, the anions are much larger than the cations, and it is the anions which form the crystal array. The smaller cations reside in the holes between the anions.

Explain the energy changes in the formation of ionic compounds.

Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion Table salt is an example of an ionic compound. Sodium and chlorine ions come together to form sodium chloride, or NaCl. The sodium atom in this compound loses an electron to become Na+, while the chlorine atom gains an electron to become Cl-.

Describe how ions form.

Ions are electrically charged particles formed when atoms lose or gain electrons. They have the same electronic structures as noble gases. Metal atoms form positive ions, while non-metal atoms form negative ions. The strong electrostatic forces of attraction between oppositely charged ions are called ionic bonds.

Define luster related to metals.

Luster is the way light interacts with the surface of a crystal, rock, or mineral. Metals are lustrous because of the free electrons they have. The free electrons can move freely in the metal causing any light incident on them to get reflected back. This reflection is specular reflection rather than diffused and thus the metal surface appears shiny or lustrous

Define malleability related to metals.

Malleability is a substance's ability to deform under pressure (compressive stress). If malleable, a material may be flattened into thin sheets by hammering or rolling. Malleable materials can be flattened into metal leaf. Many metals with high malleability also have high ductility.

Define metallic bonding.

Metallic bonding is the force of attraction between valence electrons and the metal atoms. It is the sharing of many detached electrons between many positive ions, where the electrons act as a "glue" giving the substance a definite structure. It is unlike covalent or ionic bonding.