___________ is one or two letters representing an element.

• Mass number

• Chemical bond

• Chemical symbol

• Atomic number

___________ is the simplest form of matter that has a characteristic set of properties.

• Energy

• Chemical formula

• Element

• System

___________ is the total kinetic energy of all the particles that make up the matter.

• Thermal energy

• Light energy

• Potential energy

• Chemical bond

Relative atomic masses are measured in _________.

• nano gram

• kilogram

• newton

• amu

The sum of protons and neutrons in an atom equals the _______.

• atomic number

• number of electrons

• atomic mass

• mass number

How do the isotopes of hydrogen-2 and hydrogen-3 differ?

• Hydrogen-3 has one more electron than hydrogen-2.

• Hydrogen-3 has one more proton than hydrogen-2.

• Hydrogen-3 has one more neutron than hydrogen-2.

• Hydrogen-2 has 2 neutrons while hydrogen-3 has 3 neutrons.

Answer explanation

Hydrogen-2 (deuterium) has one neutron, while hydrogen-3 (tritium) has two neutrons. Therefore, hydrogen-3 has one more neutron than hydrogen-2, making this the correct distinction between the two isotopes.

The number 80 in the bromine-80 represents _______.

• the atomic number

• the sum of protons and electrons

• the mass number

• None of the above

Answer explanation

The number 80 in bromine-80 indicates the mass number, which is the total count of protons and neutrons in the nucleus. It is not the atomic number, which represents only protons, nor the sum of protons and electrons.

Which of these statements is not true?

• Atoms of the same elements can have different masses.

• The nucleus of an atom has a positive charge.

• Atoms of isotopes have different numbers of protons.

• Atoms are mostly empty space.

Answer explanation

Atoms of isotopes have the same number of protons but different numbers of neutrons. Therefore, this statement is not true, as isotopes differ in mass, not in the number of protons.

Which of these statements is not true?

• Electrons have a negative charge.

• An electron has a mass of 1 amu.

• The nucleus of an atom is positively charged.

• The neutron is found in the nucleus of an atom.

Answer explanation

The statement "An electron has a mass of 1 amu" is not true. An electron has a very small mass, approximately 1/1836 amu, making this statement incorrect. The other statements about electrons and the nucleus are true.

How many electrons does one neutrally charged atom of argon have?

• 18

• 22

• 40

• 58

Answer explanation

A neutrally charged atom has an equal number of protons and electrons. Argon has an atomic number of 18, meaning it has 18 protons and therefore 18 electrons.