covalent bonds

polar and nonpolar covalent compounds

Having polar bonds may make a covalent compound polar. A polar compound is one in which there is a slight difference in charge between opposite ends of the molecule. All polar compounds contain polar bonds. But having polar bonds does not necessarily result in a polar compound. It depends on how the atoms are arranged. This is illustrated in Figure 7.11. Both molecules in the figure contain polar bonds, but only formaldehyde is a polar compound. Why is carbon dioxide nonpolar? The molecules of polar compounds are attracted to each other. You can see this in Figure 7.12 for water. A bond forms between the positive hydrogen end of one water molecule and the negative oxygen end of another water molecule. This type of bond is called a hydrogen bond. Hydrogen bonds are weak, but they still must be overcome when a polar substance changes from a solid to a liquid or from a liquid to a gas. As a result, polar covalent compounds may have higher melting and boiling points than nonpolar covalent compounds. To learn more about hydrogen bonding and when it occurs, see the video at this URL: (0:58). MEDIA Click image to the left or use the URL below. URL:

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why covalent bonds form

Covalent bonds form because they give atoms a more stable arrangement of electrons. Look at the hydrogen atoms in Figure 7.7. Alone, each hydrogen atom has just one electron. By sharing electrons with another hydrogen atom, it has two electrons: its own and the one in the other hydrogen atom. The shared electrons are attracted to both hydrogen nuclei. This force of attraction holds the two atoms together as a molecule of hydrogen. Some atoms need to share more than one pair of electrons to have a full outer energy level. For example, an oxygen atom has six valence electrons. It needs two more electrons to fill its outer energy level. Therefore, it must form two covalent bonds. This can happen in many different ways. One way is shown in Figure 7.8. The oxygen atom in the figure has covalent bonds with two hydrogen atoms. This forms the covalent compound water.

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polar and nonpolar covalent bonds

In some covalent bonds, electrons are not shared equally between the two atoms. These are called polar bonds. Figure 7.9 shows this for water. The oxygen atom attracts the shared electrons more strongly because its nucleus has more positively charged protons. As a result, the oxygen atom becomes slightly negative in charge. The hydrogen atoms attract the electrons less strongly. They become slightly positive in charge. For another example of polar bonds, see the video at this URL: (0:52). MEDIA Click image to the left or use the URL below. URL: In other covalent bonds, electrons are shared equally. These bonds are called nonpolar bonds. Neither atom attracts the shared electrons more strongly. As a result, the atoms remain neutral. Figure 7.10 shows an example of nonpolar bonds.

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covalent compounds

Covalent bonds between atoms of different elements form covalent compounds. The smallest, simplest covalent compounds have molecules with just two atoms. An example is hydrogen chloride (HCl). It consists of one hydrogen atom and one chlorine atom. The largest, most complex covalent molecules have thousands of atoms. Examples include proteins and carbohydrates. These are compounds in living things. Helpful Hints Naming Covalent Compounds Follow these rules in naming simple covalent compounds: The element closer to the left of the periodic table is named first. The second element gets the suffix ide. Prefixes such as di- (2) and tri- (3) show the number of each atom in the compound. These are written with subscripts in the chemical formula. Example: The gas that consists of one carbon atom and two oxygen atoms is named carbon dioxide. Its chemical formula is CO2 . You Try It! Problem: What is the name of the compound that contains three oxygen atoms and two nitrogen atoms? What is its chemical formula?

properties of covalent compounds

Covalent compounds have different properties than ionic compounds because of their bonds. Covalent compounds exist as individual molecules rather than crystals. It takes less energy for individual molecules than ions in a crystal to pull apart. As a result, covalent compounds have lower melting and boiling points than ionic compounds. Many are gases or liquids at room temperature. Covalent compounds have shared electrons. These are not free to move like the transferred electrons of ionic compounds. This makes covalent compounds poor conductors of electricity. Many covalent compounds also do not dissolve in water as all ionic compounds do.

formation of covalent bonds

A covalent bond is the force of attraction that holds together two atoms that share a pair of electrons. The shared electrons are attracted to the nuclei of both atoms. Covalent bonds form only between atoms of nonmetals. The two atoms may be the same or different elements. If the bonds form between atoms of different elements, a covalent compound forms. Covalent compounds are described in detail later in the lesson. To see a video about covalent bonding, go to this URL: (6:20). MEDIA Click image to the left or use the URL below. URL: Figure 7.7 shows an example of a covalent bond forming between two atoms of the same element, in this case two atoms of hydrogen. The two atoms share a pair of electrons. Hydrogen normally occurs in two-atom, or diatomic, molecules like this (di- means "two"). Several other elements also normally occur as diatomic molecules: nitrogen, oxygen, and all but one of the halogens (fluorine, chlorine, bromine, and iodine).

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instructional diagrams

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This diagram depicts covalent bonds in the ammonia compound. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It has 3 hydrogen atoms and 1 nitrogen atom. The nitrogen atom has 5 outer electrons, and the hydrogen atom has 1 electron. The nitrogen atom shares 2 electrons with each hydrogen atom, one provided by the nitrogen atom and the other provided by the hydrogen atom.

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This diagram shows the covalent bonds in water molecule. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The water molecule consists of two hydrogen atoms and one oxygen atom with the chemical formula of H2O. The oxygen atom has 6 electrons and each hydrogen atom has one electron. The oxygen atom shares 2 electrons with two electrons from two hydrogen atoms. So, it completes the outer most shell of oxygen atom with 8 total electrons.

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This diagram shows the covalent bonds in carbon dioxide molecule. A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The carbon dioxide molecule consists of two oxygen atoms and one carbon atom with the chemical formula of CO2. At the outer most shell of carbon atom, there are 4 electrons. Each oxygen atoms shares 2 electrons with carbon atom. So, it completes the outer most shell of carbon atom with 8 total electrons.

questions

any compound consisting of two or more nonmetals

a. covalent bond

b. hydrogen bond

c. polar bond

d. nonpolar bond

e. diatomic bond

f. polar compound

-->  g. covalent compound

Two hydrogen atoms may bond together to form a hydrogen

a. ion.

-->  b. molecule.

c. compound.

d. two of the above

covalent bond in which neither atom has an electric charge

a. covalent bond

b. hydrogen bond

c. polar bond

-->  d. nonpolar bond

e. diatomic bond

f. polar compound

g. covalent compound

An example of a covalent compound is

a. sodium fluoride.

b. calcium chloride.

-->  c. carbon dioxide.

d. all of the above

covalent bond between two atoms of the same element

a. covalent bond

b. hydrogen bond

c. polar bond

d. nonpolar bond

-->  e. diatomic bond

f. polar compound

g. covalent compound

In all covalent bonds, valence electrons are

a. lost.

b. gained.

c. shared equally.

-->  d. share

The compound that contains two oxygen atoms and one nitrogen atom is named

a. oxygen nitride.

b. dioxygen nitride.

-->  c. nitrogen dioxide.

d. nitrogen monoxide.

force of attraction holding together two atoms that share a pair of electrons

-->  a. covalent bond

b. hydrogen bond

c. polar bond

d. nonpolar bond

e. diatomic bond

f. polar compound

g. covalent compound

weak bond that forms between oppositely charged ends of two molecules

a. covalent bond

-->  b. hydrogen bond

c. polar bond

d. nonpolar bond

e. diatomic bond

f. polar compound

g. covalent compound

What is the chemical formula for the compound in question 4?

a. O2 N

b. N2 O

c. NO

-->  d. NO2

covalent bond in which the two atoms are oppositely charged

a. covalent bond

b. hydrogen bond

-->  c. polar bond

d. nonpolar bond

e. diatomic bond

f. polar compound

g. covalent compound

compound in which molecules have oppositely charged ends

a. covalent bond

b. hydrogen bond

c. polar bond

d. nonpolar bond

e. diatomic bond

-->  f. polar compound

g. covalent compound

Covalent bonds form only between atoms of different elements.

a. true

-->  b. false

A single covalent bond involves just one valence electron.

a. true

-->  b. false

Sharing electrons allows atoms to have a full outer energy level.

-->  a. true

b. false

Each hydrogen atom can form two covalent bonds.

a. true

-->  b. false

The hydrogen end of a water molecule is slightly negative in charge.

a. true

-->  b. false

Covalent bonds are found only in covalent compounds.

a. true

-->  b. false

Some covalent compounds contain atoms of just one element.

a. true

-->  b. false

Formaldehyde is an example of a covalent compound.

-->  a. true

b. false

Oxygen gas consists of individual oxygen atoms.

a. true

-->  b. false

An oxygen atom forms two covalent bonds.

-->  a. true

b. false

Oxygen always becomes negatively charged when it forms covalent bonds.

a. true

-->  b. false

In naming a covalent compound, the element closest to the right of the periodic table is named first.

a. true

-->  b. false

The second element named in a covalent compound gets the suffix ide.

-->  a. true

b. false

Polar compounds tend to have higher boiling points than nonpolar compounds.

-->  a. true

b. false

If a bond forms between calcium and chlorine, the bond is covalent.

a. true

-->  b. false

Covalent bonds may form between

a. atoms of different elements.

b. atoms of the same element.

c. ions of different elements.

-->  d. two of the above

Elements that normally occur as diatomic molecules include

a. hydrogen.

b. iodine.

c. oxygen.

-->  d. all of the above

Shared electrons in covalent bonds are always attracted to

-->  a. both nuclei.

b. both nuclei equally.

c. one nucleus more than the other.

d. one nucleus only.

How many covalent bonds must a hydrogen atom form to have a full outer energy level?

a. 0

-->  b. 1

c. 2

d. 3

An example of a polar molecule is

-->  a. H2 O.

b. CO2 .

c. O2 .

d. H2 .

Which statement about hydrogen bonds is true?

a. They are very strong.

-->  b. They form between molecules.

c. They form within molecules.

d. two of the above

Compared with ionic compounds, covalent compounds

-->  a. have lower melting points.

b. have higher boiling points.

c. are better conductors of electricity.

d. are more likely to dissolve in water.

diagram questions

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How many hydrogen atoms are there in a methane molecule?

a. 3

b. 5

-->  c. 4

d. 2

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What particle does Hydrogen (H) bond to in a nonpolar covalent bond?

a. Oxygen (O)

-->  b. Carbon (C)

c. Hydrogen (H)

d. Both O and H

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How many types of bonds are shown in the diagram?

-->  a. 2

b. 4

c. 1

d. 5

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How many oxygens does the nonpolar covalent bond have in this diagram?

a. Three

b. Four

-->  c. Two

d. Five

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How many electrons are shared in the covalent bond between two oxygen atoms?

-->  a. 4

b. 1

c. 2

d. 3

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How many electrons are shown in this diagram?

a. 4

b. 2

-->  c. 16

d. 18

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How many oxygen atoms are shown here?

a. one

-->  b. two

c. five

d. three

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What happens to the melting and boiling point of compounds that have covalent bond?

-->  a. they are higher due to their bond

b. same as other compound

c. it is weaker because they're sharing

d. no effect on the bond

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What type of bond is formed between two oxygen atoms?

a. Ionic

-->  b. Covalent

c. Hydrogen bond

d. Van der waals

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Which element is bonded to oxygen?

a. Covalent bond

b. Lone pair

c. Oxygen

-->  d. Hydrogen

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Which type of bond connects two water molecules?

a. lone pair

b. ionic bond

-->  c. hydrogen bond

d. covalent bond

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How many hydrogen atoms are represented in the diagram?

a. 2

b. 5

-->  c. 4

d. 3

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What is the force of attraction that holds together two atoms that share a pair of electrons known as?

a. Non Covalent Bonds.

b. Oxygen Bonds.

-->  c. Covalent Bond.

d. Hydrogen Bond.

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Which bond is responsible for keeping two molecules together?

-->  a. Hydrogen Bond

b. Covalent Bond

c. Metallic Bond

d. Ionic Bond

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How many hydrogen atoms are shown in this diagram?

a. 1

b. 3

-->  c. 2

d. 4

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In oxygen, how many polar covalent bonds are there?

a. 5

b. 3

c. 4

-->  d. 2

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What is the name of the weak bond formed between water molecules?

a. polar covalent bond

-->  b. Hydrogen bond

c. covalent bond

d. water bond

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How many hydrogen atoms make a methane molecule?

a. 3

b. 1

c. 2

-->  d. 4

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What bond is holding the atoms together?

a. polar bond

b. ionic bond

-->  c. covalent bond

d. non-polar bond

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How many atoms make up this compound?

a. 1

b. 2

c. 4

-->  d. 5

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How many carbon atoms are represented in the diagram?

a. 4

-->  b. 1

c. 2

d. 5

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What is a covalent bond?

a. the repulsion that keeps two neutrons apart

-->  b. The force of attraction that holds together two atoms that share a pair of electrons

c. the repulsion that keeps two eletrons apart

d. the force of attraction that holds together two atoms that share a pair of neutrons

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Which of the following will cause the molecule to become an ion?

a. The molecule loses all 4 H atoms and bond with O2

b. The molecule bonds with H2O

-->  c. The molecule loses 1 H atom

d. The molecule loses 1 H atom and bonds with OH

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How many atoms are shared in the covalent bond below?

a. 4

-->  b. 2

c. 6

d. None

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How many electrons are shown in the diagram?

a. 6

-->  b. 2

c. 10

d. 12

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How many electrons would be shared if this were a double covalent bond?

a. 8

b. 6

-->  c. 4

d. 2

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What does the C stand for in the covalent bond?

-->  a. Carbon

b. Chloride

c. Covalent

d. Chromium

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What type of bond is this?

a. shared pair

-->  b. covalent

c. single

d. double displacement

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How many covalent bonds are shown in this diagram?

a. 1

-->  b. 2

c. 3

d. 4

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How many hydrogen atoms are present in the molecule?

a. 3

b. 1

c. 4

-->  d. 2

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How many electrons are shared in a covalent bond?

a. four

b. one

c. three

-->  d. a pair

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What represents the element, hydrogen, in the diagram?

-->  a. H

b. F

c. HF

d. X

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How many elements are shown in this diagram?

a. 4

-->  b. 2

c. 1

d. 3

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What kind of bond is presented on the figure?

a. Ionic bond

b. Electric bond

c. Chemical bond

-->  d. Covalent bond

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Each hydrogen molecule is connected by what type of particles?

a. Electrons and Neutrons

-->  b. Protons and Neutrons

c. Electrons

d. Protons and Electrons

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How many covalent bonds are there in this molecule?

a. 4

b. 1

-->  c. 2

d. 6

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How many hydrogen atoms can form bonds with 1 carbon atom?

a. 2

b. 5

-->  c. 4

d. 3

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How many hydrogen molecules are depicted?

a. 1

-->  b. 4

c. 2

d. 3

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How many valence electrons are represented?

a. 1

-->  b. 6

c. 3

d. 4

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How many molecules are present?

-->  a. 2

b. 24

c. 6

d. 4

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How many electrons are shown in the diagram?

a. 16

b. 20

-->  c. 22

d. 26

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If the oxygen atom in this covalent bond has a positive charge of 8, what is the carbon's charge?

-->  a. 6

b. 5

c. 7

d. 8

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How many electrons does an oxygen atom contain?

-->  a. 6

b. 4

c. 8

d. 2

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How many Hydrogen atoms are represented in this diagram?

a. 1

b. 3

-->  c. 2

d. 4

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How many electrons did Oxygen have before forming a covalent bond with Hydrogen to become water?

a. 4

-->  b. 6

c. 1

d. 2