Midterm Review Packet Answer Key - East Boston High School (Page 4 of 6) in pdf

Open Response Questions

1. CBr

and NaBr are two compounds formed differently on the molecular level.

a. Identify the type of bond formed in each compound

CBr

contains covalent bonds while NaBr contains ionic bonds

b. Compare and contrast the two types of bonds. Include at least two similarities and two differences

between them.

S imilarities: both types of bonds involve electrons. Both also result in the formation of compounds

from two or more elements. However, ionic bonds involve complete transfer of electrons while in

covalent bonds, the electrons are shared. Also, ionic bonds involve metals and nonmetals, while

covalent bonds only involve nonmetals.

2. Imagine that you found two gold colored rods of different volumes in a laboratory stockroom. Rod

A has a mass of 28.3 g and Rod B has a mass of 14.0g.

Describe the procedures (experiment) that you would complete to determine whether or not the

two gold rods are made of the same metal. Include the lab materials you would need to use and

how you would use them.

For this experiment, I would need water, graduated cylinders, and the metal rods. I would first measure

the volume of the rods using water displacement: I would take the initial volume of water using a

graduated cylinder and then take the final volume after placing the metal rod n the graduated cylinders

of water. The difference between the initial and final volumes of water would be the volume of the

rods. Using these volumes and the masses given, I would calculate density by dividing mass by

volume. I would then compare the densities of the two rods to see if they are made of the same

materials since density is an intrinsic property, and each substance has its own unique density.

3. Sodium has an atomic number of 11 and a mass number of 23.

a. Identify the types of subatomic particles located in the nucleus of a sodium atom. Compare the

properties of each type of particle.

Protons: positively charged particles

Neutrons: neutral particles

b. Where is m ost of a sodium atom’s mass located? Explain your answer.

Most of the mass of sodium is located in the nucleus. Protons and neutrons contribute to the mass of an

atom, while electrons do not.

c. Identify the subatomic particles that are found in the energy levels outside the nucleus of a

sodium atom. Describe the number and arrangement of these particles.

Electrons are found in the energy levels outside of the nucleus. A neutral atom of sodium has a total of

11 electrons. There are 2 electrons in the first shell, 8 in the second shell, and 1 in the valence shell

d. Explain the role of electrons in a chemical reaction between atoms of two different elements.

Atoms form bonds to other atoms using their valence electrons. In the case of sodium, it would lose an

electron to a nonmetal in order to have a full valence electron shell like Neon.

4. An atom has an atomic mass of 14amu. The atom has 5 neutrons

a) What is the identity of this element? How do you know? (show your calculations)

mass# of neutrons = # of protons = atomic number.

# of protons determines the identity of an atom. 145=9. This element is fluorine (F) which has an

atomic number of 9

b) Write the isotope symbol of this element

Midterm Review Packet Answer Key - East Boston High School Page 4

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