CHEMICAL BONDING END OF UNIT TEST

Some non-metallic elements form covalent simple molecular structures involving a number of atoms. Phosphorus is one of these, forming the molecule P₄.

What is the total number number of electrons shared in the bonds of this molecule?

• 12

• 8

• 4

• 2

Answer explanation

There are six bonds in the molecule with a pair of shared electrons.

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There are various different types of structures that compounds can form, depending on their nature of bonding. A substance has an ionic structure represented in the diagram.

a. What could this substance be?

• iodine

• water

• potassium bromide

• diamond

Answer explanation

ionic compounds are formed when metallic elements bond with non-metallic elements.

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NGSS.HS-PS1-3

b. Give reasons for your answer to a

Answer explanation

The structure shown is of an ionic compound; potassium bromide is the only ionic compound in the list.

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When potassium reacts with chlorine the ionic compound potassium chloride is formed. The electronic structures of the two ions formed are the same.

⌈K 2,8,8⌉⁺ ⌈Cl 2,8,8⌉^₋

a. Explain what has happened during the reaction to form these two ions.

Answer explanation

potassium has lost an electron; chlorine has gained an electron

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b. When two chlorine atoms react with each other ions are not formed. The formular of the molecule is

Answer explanation

Most gases are diatomic molecules

c. The type of bond between the chlorine atoms is called

Answer explanation

Covalent bonds are formed between non-metallic elements; chlorine is a non-metallic element

d. Give a difference in physical properties between chlorine and potassium chloride

Answer explanation

Potassium chloride has a high melting point, whereas chlorine has a low melting point(or boiling point) / Potassium chloride is a solid, whereas chlorine is a gas

Calcium chloride is an ionic compound. When it is dissolved in water, the solution conducts electricity.

a. Explain why a solution of sodium chloride conducts electricity but solid sodium chloride does not.

Answer explanation

In calcium chloride solution the mobile ions carry the charge in solution/ the ions are fixed in position in the solid

b. In what other way can calcium chloride be made to conduct electricity?

Answer explanation

by melting it

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NGSS.HS-PS2-5

Calcium chloride has a melting point of 782^oC. Water melts at 0^oC. Use these differences to contrast the types of attractive forces involved.

Answer explanation

The ionic bonds in calcium chloride are strong electrostatic forces; intermolecular forces in water are weak interactions.

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