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     assignments -->unit 3 part 2 --> metals

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Metals

Introduces properties of the largest group of elements.

·        Identify the metals class of elements.

·        Describe properties of metals.

·        Explain why metals are good conductors of electricity.

When you think of metals, do you think of solid objects such as iron nails and gold jewelry? If so, it might surprise you to learn that the shiny liquid pouring out of the pipette in the photo above is also a metal. It’s called mercury, and it’s the only metal that normally exists on Earth as a liquid. Just what are metals, and what are their properties? Read on to find out.

What Are Metals?

Metals are elements that can conduct electricity. They are one of three classes of elements (the other two classes are nonmetals and metalloids). Metals are by far the largest of the three classes. In fact, most elements are metals. All of the elements on the left side and in the middle of the periodic table, except for hydrogen, are metals. There are several different types of metals, including alkali metals in group 1 of the periodic table, alkaline Earth metals in group 2, and transition metals in groups 3–12. The majority of metals are transition metals.

Properties of Metals

Elements in the same class share certain basic similarities. In addition to conducting electricity, many metals have several other shared properties, including those listed below. You can dig deeper into the properties of metals at this URL:http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2011/periodictable/metalsrev1.shtml.

·        Metals have relatively high melting points. This explains why all metals except for mercury are solids at room temperature.

·        Most metals are good conductors of heat. That’s why metals such as iron, copper, and aluminum are used for pots and pans.

·        Metals are generally shiny. This is because they reflect much of the light that strikes them. The mercury pictured above is very shiny.

·        The majority of metals are ductile. This means that they can be pulled into long, thin shapes, like the aluminum electric wires pictured in the Figure below.

·        Metals tend to be malleable. This means that they can be formed into thin sheets without breaking. An example is aluminum foil, also pictured in the Figure below.

Q: The defining characteristic of metals is their ability to conduct electricity. Why do you think metals have this property?

A: The properties of metals—as well as of elements in the other classes—depend mainly on the number and arrangement of their electrons.

Explaining the Properties of Metals

To understand why metals can conduct electricity, consider the metal lithium as an example. An atom of lithium is modeled below. Look at lithium’s electrons. There are two electrons at the first energy level. This energy level can hold only two electrons, so it is full in lithium. The second energy level is another story. It can hold a maximum of eight electrons, but in lithium it has just one. A full outer energy level is the most stable arrangement of electrons. Lithium would need to gain seven electrons to fill its outer energy level and make it stable. It’s far easier for lithium to give up its one electron in energy level 2, leaving it with a full outer energy level (now level 1). Electricity is a flow of electrons. Because lithium (like most other metals) easily gives up its “extra” electron, it is a good conductor of electricity. This tendency to give up electrons also explains other properties of metals such as lithium.

Summary

·        Metals are elements that can conduct electricity. Most elements are metals.

·        All metals except for mercury are solids at room temperature. Many metals are shiny, ductile, and malleable. Most are also good conductors of heat.

·        Electricity is a flow of electrons. Atoms of metals tend to give up electrons, explaining why they are good conductors of electricity. The tendency to give up electrons also explains many of the other properties of metals.

Explore More

At the following URL, click on any one of the metals in the interactive periodic table. Read the information provided about your choice of metal, and then make a poster demonstrating its structures, properties, and uses.

http://www.ptable.com/

Review

1.     What are metals?

2.     List several properties of metals.

3.     Explain why metals can conduct electricity

Nonmetals

Introduces properties of the second largest group of elements.

·        Identify the nonmetals class of elements.

·        List properties of nonmetals.

·        Explain why nonmetals vary in their reactivity and cannot conduct electricity.

The three pure substances pictured above have the distinction of being among the top ten elements that make up the human body. All three of them belong to the class of elements called nonmetals. Most of the elements that comprise the human body—as well as the majority of other living things—are nonmetals. In fact, seven of the top ten elements in your own body belong to this class of elements. What do you know about nonmetals? What are their properties, and how are they different from other elements? In this article, you’ll find out.

What Are Nonmetals?

Nonmetals are elements that generally do not conduct electricity. They are one of three classes of elements (the other two classes are metals and metalloids.) Nonmetals are the second largest of the three classes after metals. They are the elements located on the right side of the periodic table.

Q: From left to right across each period (row) of the periodic table, each element hasatoms with one more proton and one more electron than the element before it. How might this be related to the properties of nonmetals?

A: Because nonmetals are on the right side of the periodic table, they have moreelectrons in their outer energy level than elements on the left side or in the middle of the periodic table. The number of electrons in the outer energy level of an atom determines many of its properties.

Properties of Nonmetals

As their name suggests, nonmetals generally have properties that are very different from the properties of metals. Properties of nonmetals include a relatively low boilingpoint, which explains why many of them are gases at room temperature. However, some nonmetals are solids at room temperature, including the three pictured above, and one nonmetal—bromine—is a liquid at room temperature. Other properties of nonmetals are illustrated and described in the Table below.

Reactivity of Nonmetals

Reactivity is how likely an element is to react chemically with other elements. Some nonmetals are extremely reactive, whereas others are completely nonreactive. What explains this variation in nonmetals? The answer is their number of valence electrons. These are the electrons in the outer energy level of an atom that are involved in interactions with other atoms. Let’s look at two examples of nonmetals, fluorine and neon. Simple atomic models of these two elements are shown in the Figure below.

Q: Which element, fluorine or neon, do you predict is more reactive?

A: Fluorine is more reactive than neon. That’s because it has seven of eight possibleelectrons in its outer energy level, whereas neon already has eight electrons in this energy level.

Although neon has just one more electron than fluorine in its outer energy level, that one electron makes a huge difference. Fluorine needs one more electron to fill its outer energy level in order to have the most stable arrangement of electrons. Therefore, fluorine readily accepts an electron from any element that is equally “eager” to give one up, such as the metal lithium or sodium. As a result, fluorine is highly reactive. In fact, reactions with fluorine are often explosive, as you can see in the URL below. Neon, on the other hand, already has a full outer energy level. It is already very stable and never reacts with other elements. It neither accepts nor gives up electrons. Neon doesn’t even react with fluorine, which reacts with all other elements except helium.

http://www.youtube.com/watch?v=vtWp45Eewtw (6:42)

Why Most Nonmetals Cannot Conduct Electricity

Like most other nonmetals, fluorine cannot conduct electricity, and its electrons explain this as well. An electric current is a flow of electrons. Elements that readily give up electrons (the metals) can carry electric current because their electrons can flow freely. Elements that gain electrons instead of giving them up cannot carry electric current. They hold onto their electrons so they cannot flow.

Summary

·        Nonmetals are elements that generally cannot conduct electricity. They are the second largest class of elements after metals. Examples of nonmetals include hydrogen, carbon, chlorine, and helium.

·        Properties of nonmetals include a relatively low boiling point, so many nonmetals are gases. Nonmetals are also poor conductors of heat, and solid nonmetals are dull and brittle.

·        Some nonmetals are very reactive, whereas others are not reactive at all. It depends on the number of electrons in their outer energy level.

·        Reactive nonmetals tend to gain electrons. This explains why they cannot conduct electricity, which is a flow of electrons.

Explore More

Watch the video about nonmetals at the following URL, and then answer the questions below.

http://www.youtube.com/watch?v=-q1OW8vJ3wA (5:16)

1.     The science teacher in the video does an experiment in which he tests the reactivity of four nonmetal gases. How does he test them?

2.     What is the outcome of the experiment?

3.     Based on this outcome, what conclusion can you draw?

4.     Why do the gases differ in reactivity?

Review

1.     What are nonmetals?

2.     List properties of nonmetals.

3.     Explain why nonmetals vary in their reactivity.

4.     Carbon cannot conduct electricity. Why not?

Metalloids

Introduces properties of the smallest group of elements.

·        Identify the metalloids class of elements.

·        List physical properties of metalloids.

·        Explain why some metalloids react like metals and others react like nonmetals.

What is this intricate orb? It is the greatly magnified skeleton of single-celled ocean organisms call radiolarian. The skeleton is made of an element that is extremely common on Earth. In fact, it is the second most abundant element in Earth’s crust. It is also one of the most common elements in the entire universe. What is this important element? Its name is silicon, and it belongs to a class of elements called metalloids.

What Are Metalloids

Metalloids are the smallest class of elements. (The other two classes of elements aremetals and nonmetals). There are just six metalloids. In addition to silicon, they include boron, germanium, arsenic, antimony, and tellurium. Metalloids fall between metals and nonmetals in the periodic table. They also fall between metals and nonmetals in terms of their properties.

Q: How does the position of an element in the periodic table influence its properties?

A: Elements are arranged in the periodic table by their atomic number, which is the number of protons in their atoms. Atoms are neutral in electric charge, so they always have the same number of electrons as protons. It is the number of electrons in the outer energy level of atoms that determines most of the properties of elements.

Chemical Properties of Metalloids

How metalloids behave in chemical interactions with other elements depends mainly on the number of electrons in the outer energy level of their atoms. Metalloids have from three to six electrons in their outer energy level. Boron, pictured in the Figurebelow, is the only metalloid with just three electrons in its outer energy level. It tends to act like metals by giving up its electrons in chemical reactions. Metalloids with more than four electrons in their outer energy level (arsenic, antimony, and tellurium) tend to act like nonmetals by gaining electrons in chemical reactions. Those with exactly four electrons in their outer energy level (silicon and germanium) may act like either metals or nonmetals, depending on the other elements in the reaction.

Physical Properties of Metalloids

Most metalloids have some physical properties of metals and some physical properties of nonmetals. For example, metals are good conductors of both heat and electricity, whereas nonmetals generally cannot conduct heat or electricity. And metalloids? They fall between metals and nonmetals in their ability to conduct heat, and if they can conduct electricity, they usually can do so only at higher temperatures. Metalloids that can conduct electricity at higher temperatures are called semiconductors. Silicon is an example of a semiconductor. It is used to make the tiny electric circuits in computer chips. You can see a sample of silicon and a silicon chip in the Figure below.

Metalloids tend to be shiny like metals but brittle like nonmetals. Because they are brittle, they may chip like glass or crumble to a powder if struck. Other physical properties of metalloids are more variable, including their boiling and melting points, although all metalloids exist as solids at room temperature. You can learn about the properties of specific metalloids by watching the video at this URL:

http://www.youtube.com/watch?v=NO36yksPOBM (6:50)

Summary

·        Metalloids are the smallest class of elements, containing just six elements. They fall between metals and nonmetals in the periodic table.

·        How metalloids behave in chemical interactions with other elements depends mainly on the number of electrons in the outer energy level of their atoms. Metalloids may act either like metals or nonmetals in chemical reactions.

·        Most metalloids have some physical properties of metals and some physical properties of nonmetals. They fall between metals and nonmetals in their ability to conduct heat and electricity. They are shiny like metals but brittle like nonmetals. All exist as solids at room temperature.

Explore More

Because metalloids are similar in some ways to metals and in other ways to nonmetals, to understand metalloids you need to know about these other two classes of elements. Watch the following video on classes of elements. Then, using information from the video, make a table comparing and contrasting metals, nonmetals, and metalloids.

http://www.youtube.com/watch?v=q7wy8ycpE48 (5:41)

Review

1.     What are metalloids? Which elements are placed in this class of elements?

2.     Identify physical properties of metalloids that resemble those of metals.

3.     Which physical property of metalloids is like that of nonmetals?

4.     Explain the variation in how metalloids react with other elements.