classes of elements

electrons by class

The increase in electrons across the periodic table explains why elements go from metals to metalloids and then to nonmetals from left to right across the table. Look at period 2 in Figure 6.8 as an example. Lithium (Li) is a metal, boron (B) a metalloid, and fluorine (F) and neon (Ne) are nonmetals. The inner energy level is full for all four elements. This level has just one orbital and can hold a maximum of two electrons. The outer energy level is a different story. This level has four orbitals and can hold a maximum of eight electrons. Lithium has just one electron in this level, boron has three, fluorine has seven, and neon has eight.

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classes of elements and electrons

From left to right across the periodic table, each element has one more proton than the element to its left. Because atoms are always electrically neutral, for each added proton, one electron is also added. Electrons are added first to the lowest energy level possible until that level is full. Only then are electrons added to the next higher energy level.

valence electrons and reactivity

The electrons in the outer energy level of an atom are called valence electrons. It is valence electrons that are potentially involved in chemical reactions. The number of valence electrons determines an elements reactivity, or how likely the element is to react with other elements. The number of valence electrons also determines whether the element can conduct electric current. Thats because electric current is the flow of electrons. Table 6.1 shows how these properties vary in elements from each class. Metals such as lithium have an outer energy level that is almost empty. They "want" to give up their few valence electrons so they will have a full outer energy level. As a result, metals are very reactive and good conductors of electricity. Metalloids such as boron have an outer energy level that is about half full. These elements need to gain or lose too many electrons for a full outer energy level to come about easily. As a result, these elements are not very reactive. They may be able to conduct electricity but not very well. Some nonmetals, such as bromine, have an outer energy level that is almost full. They "want" to gain electrons so they will have a full outer energy level. As a result, these nonmetals are very reactive. Because they only accept electrons and do not give them up, they do not conduct electricity. Other nonmetals, such as neon, have a completely full outer energy level. Their electrons are already in the most stable arrangement possible. They are unreactive and do not conduct electricity. Element Description Element Lithium Description Lithium (Li) is a highly reactive metal. It has just one electron in its outer energy level. Lithium reacts explosively with water (see picture). It can react with moisture on skin and cause serious burns. Boron Boron (B) is a metalloid. It has three valence electrons and is less reactive than lithium. Boron compounds dissolved in water form boric acid. Dilute boric acid is weak enough to use as eye wash. Bromine Bromine (Br) is an extremely reactive nonmetal. In fact, reactions with fluorine are often explosive, as you can see in the URL below. Neon (Ne) is a nonmetal gas with a completely filled outer energy level. This makes it unreactive, so it doesnt combine with other elements. Neon is used for lighted signs like this one. You can learn why neon gives off light at this link: Neon

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metals

Metals are elements that are good conductors of electricity. They are the largest of the three classes of elements. In fact, most elements are metals. Look back at the modern periodic table (Figure 6.3) in this chapters lesson "How Elements Are Organized." Find the metals in the table. They are all the elements that are color-coded blue. Examples include sodium (Na), silver (Ag), and zinc (Zn). Metals have relatively high melting points, so almost all are solids at room temperature. The only exception is mercury (Hg), which is a liquid. Most metals are also good conductors of heat. Thats why they are used for cooking pots and stovetops. Metals have other characteristic properties as well. Most are shiny, ductile, and malleable. These properties are illustrated in Figure 6.5. You can dig deeper into the properties of metals at this URL:

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metalloids

Metalloids are elements that fall between metals and nonmetals in the periodic table. Just seven elements are metalloids, so they are the smallest class of elements. In Figure 6.3, they are color-coded orange. Examples of metalloids include boron (B), silicon (Si), and germanium (Ge). Metalloids have some properties of metals and some properties of nonmetals. For example, many metalloids can conduct electricity but only at certain temperatures. These metalloids are called semiconductors. Silicon is an example. It is used in computer chips. It is also the most common metalloid on Earth. It is shiny like a metal but brittle like a nonmetal. You see a sample of silicon in Figure 6.7. The figure also shows other examples of metalloids. You can learn more about the properties of metalloids at this URL: http://library.thinkquest.org/3659/p

nonmetals

Nonmetals are elements that do not conduct electricity. They are the second largest class of elements. Find the nonmetals in Figure 6.3. They are all the elements on the right side of the table that are color-coded green. Examples of nonmetals include helium (He), carbon (C), and oxygen (O). Nonmetals generally have properties that are the opposite of those of metals. They also tend to vary more in their properties than metals do. For example, nonmetals have relatively low boiling points, so many of them are gases at room temperature. But several nonmetals are solids, including carbon and phosphorus (P). One nonmetal, bromine (Br), is a liquid at room temperature. Generally, nonmetals are also poor conductors of heat. In fact, they may be used for insulation. For example, the down filling in a down jacket is mostly air, which consists mainly of nitrogen (N) and oxygen (O). These nonmetal gases are poor conductors of heat, so they keep body heat in and cold air out. Solid nonmetals are dull rather than shiny. They are also brittle rather than ductile or malleable. You can see examples of solid nonmetals in Figure 6.6. You can learn more about specific nonmetals with the interactive table at this URL: http://library.thinkquest.org/36

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instructional diagrams

No diagram descriptions associated with this lesson

questions

Most metals are

a. shiny.

b. good conductors of heat.

c. solids are room temperature.

-->  d. all of the above

Most metals are

a. dull.

b. brittle.

-->  c. ductile.

d. all of the above

If an element is ductile, this means that it can be

a. used as an insulator.

-->  b. pulled into long thin shapes.

c. used to conduct electricity.

d. crushed into a powder.

A nonmetal is an element that

a. exists only as a gas or liquid.

b. is completely unreactive.

-->  c. cannot conduct electricity.

d. is shiny and malleable.

Nonmetals tend to have properties that are

a. very similar to the properties of metals.

b. in between those of metals and metalloids.

-->  c. more variable than the properties of metals.

d. none of the above

Which of the following elements is a metal?

a. phosphorus

b. selenium

-->  c. lithium

d. boron

Which statement about valence electrons is true?

a. They are located in the outer energy level of an atom.

b. They are potentially involved in chemical reactions.

c. They determine whether an element can conduct electricity.

-->  d. all of the above

Solid nonmetals are

a. malleable.

b. brittle.

c. dull.

-->  d. two of the above

Which of the following elements is a nonmetal?

-->  a. sulfur

b. aluminum

c. silver

d. zinc

If an element is malleable, this means that it can

a. be formed into long thin shapes like wires.

-->  b. be formed into thin sheets without breaking.

c. be used to conduct electric current.

d. be used as an electric insulator.

Which of the following elements is a metalloid?

a. copper

b. helium

c. phosphorus

-->  d. germanium

Which element has a completely filled outer energy level?

a. lithium

b. boron

c. fluorine

-->  d. neon

class of elements that do not conduct electricity

a. metals

b. metalloids

-->  c. nonmetals

d. mercury

e. ductile

f. bromine

g. brittle

word that describes most solid nonmetals

a. metals

b. metalloids

c. nonmetals

d. mercury

e. ductile

f. bromine

-->  g. brittle

smallest class of elements

a. metals

-->  b. metalloids

c. nonmetals

d. mercury

e. ductile

f. bromine

g. brittle

All metalloids are solids are room temperature.

-->  a. true

b. false

only nonmetal that is a liquid at room temperature

a. metals

b. metalloids

c. nonmetals

d. mercury

e. ductile

-->  f. bromine

g. brittle

Nonmetals are the second largest class of elements.

-->  a. true

b. false

word that describes most metals

a. metals

b. metalloids

c. nonmetals

d. mercury

-->  e. ductile

f. bromine

g. brittle

only metal that is a liquid at room temperature

a. metals

b. metalloids

c. nonmetals

-->  d. mercury

e. ductile

f. bromine

g. brittle

Elements with eight valence electron are unreactive.

-->  a. true

b. false

class of elements that conduct electricity

-->  a. metals

b. metalloids

c. nonmetals

d. mercury

e. ductile

f. bromine

g. brittle

Fluorine is an example of a metalloid.

a. true

-->  b. false

Nonmetals tend to give up electrons.

a. true

-->  b. false

Metals have relatively high melting points.

-->  a. true

b. false

Carbon is an example of a metalloid.

a. true

-->  b. false

Almost all nonmetals are solids are room temperature.

a. true

-->  b. false

Some nonmetals are semiconductors.

a. true

-->  b. false

Silicon is the most common metalloid on Earth.

-->  a. true

b. false

Metals generally have fewer valence electrons than nonmetals.

-->  a. true

b. false

The number of valence electrons determines an elements reactivity.

-->  a. true

b. false

Elements that want to gain electrons are usually metals.

a. true

-->  b. false

The ability of an element to conduct electricity depends on its number of neutrons.

a. true

-->  b. false

Neon is more reactive than fluorine.

a. true

-->  b. false

diagram questions

No diagram questions associated with this lesson