Atomic theory

Who was the first person to come up with the atomic theory and called atoms "atomos" meaning indivisible?

• Albert Einstein
• Democritus
• John Dalton

• Aristotle

Which of the following has a positive charge?

• electron

• anion

• neutron

• proton

What is the atomic weight of a hypothetical element consisting of two isotopes, one with mass = 64.23 amu (26.0%), and one with mass = 65.32 amu?

• 66.50 amu
• 65.0 amu

• 64.21 amu

• 63.75 amu

The atomic Mass of an atom is equal to the number of ______ plus the number of ______.

• neutrons; electrons
• electrons; protons
• protons; isotopes
• protons; neutrons

The smallest unit of matter that can enter into chemical reactions and is nondivisible by chemical means is called a(an) _____

• atom
• nuetron

• electron
• molecule

Which of the following statements is true?

• Protons have a positive charge and are the main unit that helps bond electrons to each other.

• Neutrons have a neutral charge and equal the number of protons.

• Electrons have a positive charge and equal the number of protons.
• Electrons have a negative charge and equal the number of protons.

______ are atoms that have the same number of protons but differ in the number of neutrons.

• Elements
• Isotopes
• ions

• Compounds

Chlorine has an atomic number of 17 and is found in group 7A. How many electrons are in the outermost shell?

• 1

• 7
• 17

• 5

The carbon atom has an atomic number of 6 and an atomic weight of 12. Therefore, a carbon atom has ______ protons.

• 6
• 12
• 8
• 4

Atoms such as sodium, potassium, calcium or hydrogen, all gain electrons and become negatively charged.

• Sodium and potassium are noble gases that do not react.
• True

• Hydrogen atoms lose neutrons and become negatively charged.
• False

Answer explanation

If an atom or molecule gains an electron, it becomes negatively charged (an anion), and if it loses an electron, it becomes positively charged (a cation). These elements are metals so they loose electrons except for hydrogen.