milli 8th Grade Science Semester Exam Part 1: Chemistry 2023_ADV/GT/STEM

Student Full Name

Science Class Period

1. How many protons, neutrons, and electrons are present in an atom of hafnium, Hf, with a mass number of 178?

• A. 72 protons, 178 neutrons, 106 electrons
• B. 72 protons, 106 neutrons, 72 electrons
• C. 178 protons, 250 neutrons, 72 electrons
• D. 106 protons, 72 neutrons, 106 electrons

2. A model of a beryllium atom is shown below. What types of particles are found in the cloud surrounding the atom's nucleus?

• A. Positively charged particles and negatively charged particles
• B. Negatively charged particles only
• C. Neutral particles and positively charged particles
• D. Positively charged particles only

3. What is the mass number of a potassium (K) atom that has 20 neutrons?

• A. 18
• B. 19
• C. 20
• D. 39

4. Which of the following best describes an electron?

• A. It has no charge and about the same mass as a proton.
• B. It has a negative charge and much less mass than a proton.
• C. It has a positive charge and much more mass than a neutron.
• D. It has a negative charge and about the same mass as a neutron.

5. Four students were asked to name the parts of an atom that determine the atom's identity and chemical properties. The students' responses are shown in the table below. Which student's responses are correct?

• A. Student 1
• B. Student 2
• C. Student 3
• D. Student 4

6. Tin, Sn, is a soft white metal. It has a low melting point compared with other metals. Tin is widely used as a coating for cans of food. Which statement accurately describes atoms of Tin?

• A. Tin atoms have 50 protons.
• B. Tin atoms have five valence electrons.
• C. Tin atoms have 119 neutrons.
• D. Tin atoms have 68 electrons.

7. The atoms of a certain element each contain 11 protons and 1 valence electron. Which statement correctly identifies this element and describes its chemical reactivity?

• A. The element is sodium, and it is highly reactive
• B. The element is fluorine, and it is not very reactive
• C. The element is sodium, and it is not very reactive
• D. The element is fluorine, and it is highly reactive

8. A chemist is identifying the elements present in a sample of seawater. What characteristic of an element's atoms always determines the element's identity?

• A. The number of protons.
• B. The number of neutrons.
• C. The location of valence electrons.
• D. The number of valence electrons.