Chemistry Chapter 4

Dalton's Atomic Theory

explains that the conservation of mass in chemical reactions is the result of the separation, combination, or rearrangement of atoms—atoms that are not created, destroyed, or divided in the process.

atom

The smallest particle of an element that retains the properties of the element is called

cathode ray

This ray, originating from the cathode and traveling to the anode, was called

electron

Negatively charged particles

nucleus

Almost all of its mass were contained in a tiny,dense region in the center of the atom, which he called

proton

Positively charged particles

neutron

has no electric charge.

atomic number

The number of protons in an atom is referred to as

isotopes

Atoms with the same number of protons but different numbers of neutrons are called

mass number

the sum of the atomic number (or number of protons) and neutrons in the nucleus.

atomic mass number (amu)

defined as one-twelfth the mass of a carbon-12 atom.

atomic mass

an element is the weighted average mass of the isotopes of that element.

radioactivity

In the late 1890s, scientists noticed that some substances spontaneously emitted radiation in a process

radiation

The rays and particles emitted by the radioactive material

nuclear reaction

A reaction that involves a change in an atom's nucleus

radioactive decay

Unstable nuclei lose energy by emitting radiation in a spontaneous process

alpha radiation

The radiation that was deflected toward the negatively charged plate

alpha particle

contains two protons and two neutrons, and thus has a 2+ charge, which explains why alpha particles are attracted to the negatively charged plate

nuclear reaction

a new element, radon (Rn), is created as a result of the alpha decay of the unstable radium-226 nucleus. It shows the atomic numbers and mass numbers of the particles involved. The mass number is conserved in nuclear equations.

beta radiation

The radiation that was deflected toward the positively charged plate

beta particle

is an electron with a 1- charge. The negative charge of the beta particle explains why it is attracted to the positively charged plate

gamma ray

a high-energy radiation that possesses no mass and is denoted by the symbol γ. Because they are neutral, gamma rays are not deflected by electric or magnetic fields. They usually accompany alpha and beta radiation, and they account for most of the energy lost during radioactive decays.

Describe an atom of plutonium?

It cannot be divided into smaller particles that retain all the properties of plutonium

Neptunium's only naturally occurring isotope , 93 237 Np, decays by emitting one alpha particle, one beta particle, and one gamma ray. What is the new atom formed from this decay?

241 93 Np

Which type of matter has a definite composition throughout and is made of more than one type of element?

241 93 Np

The Moon is approximately 384,400 km from Earth. What is this value in scientific notation?

3.844 x 10 to the 5th power km

Why does an atom have no net electric charge?

The positively charged neutrons cancel out the negatively charged electrons

How many neutrons, protons, and electrons does 52 126 Te have?

74 neutrons, 52 protons, 74 electrons

What makes up most of the volume of an atom?

empty space

Assume that Element Q has the following three isotopes: 248 Q, 252 Q, and 259 Q. If the atomic mass of Q is 258.63, which of its isotopes is most abundant? Explain your answer.

259 Q is the most abundant isotope because the average atomic mass is close to 259. If a different isotope was more abundant, the average atomic mass would be much lower.

Iodine-131 undergoes radioactive decay to form an isotope with 54 protons and 77 neutrons. What type of decay occurs in this isotope? Explain how you can tell.

Beta decay; the atomic number changes from 53 (iodine) to 54 (xenon), where the mass number does not change at all