Covalent Bonds Gizmo 5 mark test answers PDF

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Questions & Answers 1. In this model of a molecule of ammonia, NH3, how many covalent bonds are represented?

A. 1 covalent bond B. 2 covalent bonds C. 3 covalent bonds D. 4 covalent bonds

Correct Answer: C. 3 covalent bonds Explanation: The diagram shows that the nitrogen atom in ammonia forms a shared https://gizmos.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=512&ClassID=5314431

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orbit for two electrons with each hydrogen atom. Each pair of electrons in a shared orbit represents one covalent bond. In this case, there are three pairs of shared electrons, or three covalent bonds.

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2. The image below shows two nitrogen atoms. For these two atoms to form a stable molecule, N2, how many electrons would have to be part of covalent bonds?

A. 0 electrons B. 2 electrons C. 4 electrons D. 6 electrons

Correct Answer: D. 6 electrons Explanation: A single nitrogen atom has ve electrons in its outer energy level to start, and will be most stable with an octet, or 8 electrons in its outer level. When forming a covalent molecule with another nitrogen atom, each atom shares 3 electrons, forming 3 covalent bonds with 2 electrons each. So, there are 6 electrons involved in covalent bonds. This can be veried by looking at the Lewis diagram of a nitrogen molecule shown below. (Each bar represents a covalent bond.)

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3. How many covalent bonds are there in one molecule of carbon dioxide, CO2 ?

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A. 0 covalent bonds B. 2 covalent bonds C. 4 covalent bonds D. 6 covalent bonds

Correct Answer: C. 4 covalent bonds Explanation: Carbon dioxide, CO2, is made up of one carbon atom covalently bonded with two oxygen atoms. Carbon starts with 4 valence electrons, needing to share 4 more electrons to form a stable octet. Meanwhile each oxygen atom starts with 6 valence electrons and needs to share 2 additional atoms to be stable. So, the carbon atom forms two bonds with each of the two oxygen atoms, for a total of 4 covalent bonds. Each covalent bond is represented by a dash in the Lewis diagram.

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4. Bromine is a halogen, one of the elements in the same column of the periodic table of elements as uorine. Like uorine, one bromine atom can form a diatomic covalent molecule with another bromine atom. Which of the following images represents a stable molecule of bromine, Br2 ? (Note: Inner electrons have been hidden.)

A. Diagram A B. Diagram B C. Diagram C D. Diagram D

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Correct Answer: B. Diagram B Explanation: Each bromine atom starts with 7 electrons in its outer energy level. This means that together, they will form one covalent bond that shares two electrons between them. In the second snapshot, you can see that each atom has 6 electrons orbiting in its own outer energy level and that there is a pair of electrons in the shared orbit. Each atom is orbited by 8 electrons, and the molecule is stable.

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5. Hydrogen cyanide is poisonous liquid that has a faint, almond-like smell. One molecule of hydrogen cyanide (HCN) is made up of one hydrogen atom, one carbon atom, and one nitrogen atom, shown below. Which of the answer choices shows the correct Lewis dot diagram for hydrogen cyanide?

A. Diagram A B. Diagram B C. Diagram C D. Diagram D

Correct Answer: D. Diagram D Explanation: To be stable, a hydrogen atom needs to have 2 electrons in orbit around its nucleus. In this diagram, the hydrogen atom is sharing two electrons in a covalent bond with the carbon atom. This is represented by a line between the H and the C. The carbon atom has four covalent bonds, one with hydrogen and three with nitrogen (the three lines connecting the C to the N). Because each covalent bond has two https://gizmos.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=512&ClassID=5314431

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electrons, the carbon atom has a full, stable complement of 8 electrons in the outer orbit around its nucleus. Nitrogen has two of its own electrons, as represented by the dots to the right of the N, and 6 electrons shared in covalent bonds with the carbon atom. So, nitrogen also effectively has a total of 8 electrons in its outer energy level. This means all the atoms in the diagram are stable.

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