8th Unit 1 & 2 Review

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

• 72 protons, 178 neutrons, 106 electrons

• 72 protons, 106 neutrons, 72 electrons

• 178 protons, 250 neutrons, 72 electrons

• 106 protons, 72 neutrons, 106 electrons

In the early 1900s many scientist thought that an atom consisted of a positive substance with negative charges scattered throughout the substance. Then Ernest Rutherford completed an experiment that changed the concept of an atom. His discovery led to the understanding that an atom consists of mostly empty space with -

• protons orbiting a dense nucleus made of electrons and neutrons

• electrons orbiting a dense nucleus made of protons and neutrons

• neutrons and protons orbiting a cloud of electrons

• electrons and protons orbiting a cloud of neutrons

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

• Positively charged particles and negatively charged particles

• Negatively charged particles only

• Neutral particles and positively charged particles

• Positively charged particles only

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

• 18

• 19

• 20

• 39

Which of the following best describes an electron?

• It has no charge and about the same mass as a proton

• It has a negative charge and much less mass than a proton

• It has a positive charge and about the same mass as a neutron

• It has a negative charge and about the same mass as a neutron

An atom has 25 protons, 30 neutrons, and 25 electrons. What is the charge of the atom's nucleus?

• +25

• +30

• -25

• -30

Which of these best describes one of the subatomic particles that could be found at location x in the model of an atom shown above?

• It has mass but no charge

• It has no mass and a positive charge

• It has a large mass and a negative charge

• It has no mass and an equal number of positive and negative charges

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. Which student's responses are correct?

• Student 1

• Student 2

• Student 3

• Student 4

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?

• Tin atoms have 50 protons

• Tin atoms have five valence electrons

• Tin atoms have 119 neutrons

• Tin atoms have 68 electrons

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?

• The element is sodium, and it is highly reactive

• The element is fluorine, and it is not very reactive

• The element is sodium, and it is not very reactive

• The element is fluorine, and it is highly reactive