Chem Honors Unit 1

deuterium isotope

The ________ has one proton and one neutron, and tritium has one proton and two neutrons.

Daltons theory

________ explains the law of multiple proportions quite simply: The compounds differ in the number of atoms of each kind that combine.

Dalton

________ made no attempt to describe the structure or composition of atoms- he had no idea what an atom is really like.

Rutherford

The atoms positive charges, ________ proposed, are all concentrated in the nucleus, a dense central core within the atom.

Cha485

________ 2.3 Atomic Number, Mass Number, and Isotopes 35 proton, and the neutron are the three fundamental components of the atom that are important in chemistry.

symbols N

The ________ and S denote the north and south poles of the magnet.

electromagnetic theory

According to ________, a moving charged body behaves like a magnet and can interact with electric and magnetic fields through which it passes.

Electrons

________ are normally associated with atoms.

Beta

________) (rays, or particles, are electrons and are deflected by the negatively charged plate.

Elements

________ are composed of extremely small particles, called atoms.

New Zealand

In 1910 the ________ physicist Ernest Rutherford, who had earlier studied with Thomson at Cambridge University, decided to use particles to probe the structure of atoms.

chemical properties

All atoms of a given element are identical, having the same size, mass, and ________.

chemical reaction

A(n) ________ involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction.

electrical neutrality

To maintain ________, an atom must contain an equal number of positive and negative charges.

English physicist

A(n) ________, J. J. Thomson, used a cathode ray tube and his knowledge of electromagnetic theory to determine the ratio of electric charge to the mass of an individual electron.

1895

Radioactivity In ________, the German physicist Wilhelm Röntgen noticed that cathode rays caused glass and metals to emit very unusual rays.

1890s

The Electron In the ________ many scientists became caught up in the study of radiation, the emission and transmission of energy through space in the form of waves.

Greek philosopher Democritus

The ________ expressed the belief that all matter consists of very small, indivisible particles, which he named atomos (meaning uncuttable or indivisible)

hydrogen

With the exception of ________, isotopes of elements are identified by their mass numbers.

Ions Figure 24

Alpha) (rays consist of 2 Atoms, Molecules, and ________ (a) A cathode ray produced in a discharge tube traveling from the cathode (left) to the anode (right)

Daltons

________ work marked the beginning of the modern era of chemistry.

Chadwick

When ________ bombarded a thin sheet of beryllium with particles, a very high energy radiation similar to rays was emitted by the metal.

Rays

________ consist of negatively charged particles (electrons) and are therefore attracted by the positively charged plate.

large deflection

Whenever an particle came close to a nucleus in the scattering experiment, it experienced a large repulsive force and therefore a(n) ________.

Cathode Ray Tube ARIS

Animation: ________, Animations cha4 2.2 The Structure of the Atom 31 In some experiments, two electrically charged plates and a magnet were added to the outside of the cathode ray tube (see Figure 2.3)

Rutherford

________ and others postulated that there must be another type of subatomic particle in the atomic nucleus; the proof was provided by another English physicist, James Chadwick, in 1932.

Electrons

________ are shown as "clouds "around the nucleus.

Chemical reactions

________ usually involve a gain or loss of heat and other forms of energy.

In this case, the ratio of the atoms of element X to the atoms of element Y is 2

1

Daltons theory explains the law of multiple proportions quite simply

The compounds differ in the number of atoms of each kind that combine

Thus, the ratio of oxygen in carbon monoxide to oxygen in carbon dioxide is 1

2

Animation

Cathode Ray Tube ARIS, Animations cha4 2.2 The Structure of the Atom 31 In some experiments, two electrically charged plates and a magnet were added to the outside of the cathode ray tube (see Figure 2.3)

Thereafter, in a series of experiments carried out between 1908 and 1917, R. A. Millikan, an American physicist, found the charge of an electron to be 1.6022  1019 C. From these data he calculated the mass of an electron

which is an exceedingly small mass

Animation

Millikan Oil Drop ARIS, Animations cha48518_c fluoresce

(a) (b) (c)

+ α γ β Radioactive substance Lead block Figure 2.5 Three types of rays emitted by radioactive elements

Animation

Alpha, Beta, and Gamma Rays ARIS, Animations cha 2.2 The Structure of the Atom 33 positively charged particles, called particles, and therefore are deflected by the positively charged plate

The Proton and the Nucleus By the early 1900s, two features of atoms had become clear

They contain electrons, and they are electrically neutral

To quote Rutherfords initial reaction when told of this discovery

"It was as incredible as if you had fired a 15-inch shell at a piece of tissue paper and it came back and hit you."

Animation

-Particle Scattering ARIS, Animations Slit Detecting screen Gold foil (a) (b) α Particle emitter Figure 2.7 (a) Rutherfords experimental design for measuring the scattering of particles by a piece of gold foil

Therefore, the ratio of the mass of a helium atom to that of a hydrogen atom should be 2

1

In reality, however, the ratio is 4

1

In the helium nucleus there are two protons and two neutrons, but in the hydrogen nucleus there is only one proton and no neutrons; therefore, the ratio is 4

1

The accepted way to denote the atomic number and mass number of an atom of element X is as follows

mass number A ZX atomic number atomic number  number of neutrons mass number number of protons  number of neutrons Charge Particle Mass (g) Coulomb Charge Unit Electron* 9.10938  1028 1.6022  1019 1 Proton 1.67262  1024 1.6022  1019 1 Neutron 1.67493  1024 0 0 *More refined experiments have given us a more accurate value of an electrons mass than Millikans

TABLE 2.1 Mass and Charge of Subatomic Particles cha48518_ch0 Thus, for the isotopes of hydrogen, we write As another example, consider two common isotopes of uranium with mass numbers of 235 and 238, respectively

The first isotope is used in nuclear reactors and atomic bombs, whereas the second isotope lacks the properties necessary for these applications