Chemistry: Chapter 4

Cathode Rays Discovery

- cathode rays were stream of charged particles. - the particles carried a negative charge.

What is the mass of an electron?

9.1 x 10 to the negative 28th power in grams

What did J.J. Thomson propose to answer this question: If electrons are part of all matter and they possess a negative charge, how can all matter be neutral?

A model of the atom that became that became known as the plum pudding model.

Robert Millikan

American physicist that determined the charge of an electron using the oil-drop apparatus.

Dalton and conservation of mass

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

Sir William Crookes

English physicist

Rutherford's experiment

In this, a narrow beam of alpha particles was aimed at a thin sheet of gold foil. A zinc-sulfide-coated screen surrounding the gold foil produced a flash of light when struck by an alpha particle. By noting where the flashes occurred, the scientists could determine if the atoms in the gold foil deflected the alpha particles.

Did Democritus ever prove his ideas?

No, he did not have the ability to conduct controlled experiments so he could not test the vailidity of his ideas.

Does matter have a charge?

No, matter is neutral- it has no electric charge.

Was Dalton's theory true?

Not all of it. For example, Dalton was wrong about atoms being indivisible because they can be divided into several subatomic particles. He was also wrong about all atoms of a given element having identical properties, those atoms can have slightly different masses.

James Chadwick

Rutherford's coworker, English physicist that showed that the nucleus also contained another subatomic neutral particle, called the neutron.

What did scientists conclude based on the cathode rays?

The ray's negative particles were found in all forms of matter.

Did Dalton ever prove his ideas?

Yes, he was able to perform experiments that allowed him to refine and support his hypothesis thanks to advancements in science.

Who is Democritus?

a Greek philosopher that was the first person to propose the idea that matter was not infinitely divisible. - believed matter was made up of tiny individual particles called atoms, which move through empty space. - believed that atoms were solid, homogeneous and could not be created, destroyed, or further divided. - different kinds of atoms have different shapes and sizes. - size, shape, and movement of atoms determine the properties of matter.

Aristotle

a Greek philospher that rejected the notion of atoms because it did not agree with his own ideas of nature. - he believed atoms cannot move through empty space because it does not exist

neutron

a subtaomic particle that has a mass nearly equal to that of a proton, but it carries no electric charge

Ernest Rutherford

began to study how positively charged alpha particles interacted with solid matter. He conducted an experiment to see if alpha particles would be deflected as they passed through a thin gold foil; determines properties of the nucleus, including charge, relative size, and density

How are electrons held within the atom?

by their attraction to the positively charged nucleus.

Rutherford's model of the atom

concluded the plum pudding model was incorrect but believed: - calculated that an atom consisted mostly of empty space through which the electrons move. - also concluded that almost all of the atom's positive charge and almost all of its mass were contained in the nucleus.

plum pudding model

consisted of a spherically shaped atom composed of a uniformly distributed positive charge in which the individual negatively charged electrons resided.

Model of the Atom

electron, the proton, and the neutron - atoms are spherically chaped, with a small, dense nucleus of positive charge surrounded by one or more negatively charged electrons. - most of an atom consists of fast-moving electrons traveling through the empty space surrounding the nucleus. - electrons are held within the atom by their attraction to the positively charged nucleus. - nucleus, which is composed of neutral neutrons and positively charged protons, contains all of an atom's positive charge and more than 99.97% of its mass. It occupies only about 1/10,000 of the volume of the atom. - Because an atom is electrically neutral, the number of protons in the nucleus equals the number of electrons surrounding the nucleus

What did they call these negatively charged particles that are part of all forms of matter?

electrons

J. J. Thomson

he concluded that the mass of the charged particles was much less than that of a hydrogen atom, the lightest known atom; he had identified the first subatomic particle- the electron.

Louis De Braglie

he discovered that electrons behave like waves (light) and that all matter has wave properties

What did Rutherford change later on?

he refined the concept of the nucleus and concluded that the nucleus contained protons.

What did Aristotle believe?

matter was composed of earth, water, air, and fire.

protons definition

positively charged particles; subatomic particle carrying a charge equal to but opposite that of an electron, has a charge of 1+.

Dalton's Atomic Theory

proposed in 1803 and says the following: - matter is composed of extremely small particles called atoms. - atoms are indivisible and indestructible - atoms of a given element are identical in size, mass, and chemical properties. - atoms of a specific element are different from those of another element. - different atoms combine in simple whole-number ratios to form compounds. - in a chemical reaction, atoms are separated, combined or rearranged.

What did Neils Bohr discover?

proposed that electrons circle in orbits around the nucleus; atoms have up to 7 orbitals, depends on the # of electrons. when electrons jump from orbitals, they release or emit energy

Neils Bohr

publishes a theory of atomic structure relating the electron arrangement in atoms and atomic chemical properties

1968

quarks, smaller particles than atoms, were discovered by scientists

Heisenberg's Uncertainty Principal

says that if electrons behave in wave manner, it's impossible to determine simultaneously both position and velocity of electrons or any particle.

John Dalton

schoolteacher in England whose work marks the beginning of the development of the modern atomic theory.

atom definition

smallest particle of an element that retains the properties of the element.

nucleus

tiny, dense region in the center of the atom; because the nucleus occupies such a small place and contains most of an atom's mass, it is incredibly dense