Chapter 2 Review Questions
State and explain the law of conversation of mass
In a chemical reaction matter is nether create nor destroyed. In a chemical reaction the total mass doesn't change
What is a mole? How is the mole concept useful in chemical calculations?
A mole is an amount of material. It is defined as the amount of material containing 6.0221421 x 10" particles (Avogadro's number). The numerical value of the mole is defined as being equal to the number of atoms in exactly 12 grams of pure carbon-12. It is useful for converting number of atoms to moles of atoms and moles of atoms to number of atoms.
What is the Brownian motion? How is it related to the development of the idea that matter is particulate?
First described by Scottish botanist Robert Brown, Brownian motion is the random motion of particles suspended in a fluid (a liquid or a gas). This motion is the result of the collision of these particles with the moving atoms or molecules (i.e., the particles) in the fluid
Explain the Millikan's oil drop experiment and how it led to the measurement of the electron's charge of the electron so important?
In Millikan's oil drop experiment, oil was sprayed into fine droplets using an atomizer. The droplets were allowed to fall under the influence of gravity through a small hole into the lower portion of the apparatus where they could be viewed. During their fall, the drops would acquire electrons that had been produced by the interaction of high-energy radiation with air. These charged drops interacted with two electrically charged plates within the apparatus. The negatively charged plate at the bottom of the apparatus repelled the negatively charged drops. By varying the voltage on the plates, the fall of the charged drops could be slowed, stopped, or even reversed. From the voltage required to halt the free fall of the drops and from the masses of the drops themselves, Millikan calculated the charge of each drop. He then reasoned that because each drop must contain an integral number of electrons, the charge of each drop must be a whole-number multiple of the electron's charge. The magnitude of the charge of the electron is of tremendous importance because it determines how strongly an atom holds its electrons.
Explain how a mass spectrometer works
In a mass spectrometer, the sample is injected into the instrument and vaporized. The vaporized atoms are then ionized by an electron beam. The electrons in the beam collide with the vaporized atoms, removing electrons from the atoms and creating positively charged ions. Charged plates with slits in them accelerate the positively charged ions into a magnetic field, which deflects them. The amount of deflection depends on the mass of the lons lighter ions are deflected more than heavier ones are. Finally, the ions strike a detector and produce an electrical signal that is recorded.
How and by whom was the electron discovered? What basic properties of the electron were reported with its discovery?
In the late 1800s, an English physicist named J. J. Thomson performed experiments to probe the properties of cathode rays. Thomson found that these rays were actually streams of particles with the following properties: They traveled in straight lines, they were independent of the composition of the material from which they originated, and they carried a negative electrical charge. He measured the charge-to-mass ratio of the particles and found that the cathode ray particle was about 2000 times lighter than hydrogen.
What are isotopes? What is percent natural abundance of isotopes?
Isotopes are atoms with the same number of protons but different numbers of neutrons. The percent natural abundance is the relative amount of each different isotope in a naturally occurring sample of a given element.
Describe the two different notations used specify isotopes and give an example of each
Isotopes can be symbolized as X, ***** A is the mass number, Z is the atomic number, and X is the chemical symbol. A second notation is the chemical symbol (or chemical name) followed by a hyphen and the mass number of the iso- tope, such as X-A, where X is the chemical symbol or name and A is the mass number. The carbon isotope with a mass of 12 would have the symbol C or C-12 or carbon-12
How do you predict the charges of ions formed by main-group elements?
Main-group metals tend to lose electrons, forming cations with the same number of electrons as the nearest noble gas. Main-group nonmetals tend to gain electrons, forming anions with the same number of electrons as the nearest following noble gas
If matter is mostly empty spaces as suggested by Rutherford, then why does it appear so solid.
Matter appears solid because the variation in its density is on such a small scale that our eyes cannot see it.
Describe the characteristic properties of metals, nonmetals, and metalloids
Metals are found on the left side and in the middle of the periodic table. They are good conductors of heat and electricity: they can he pounded into flat sheets (malleable), they can be drawn into wires (ductile), they are often shiny, and they tend to lose electrons when they undergo chemical changes Nonmetals are found on the upper-right side of the periodic table. Their properties are more varied: Some are solids at room temperature, while others are liquids or gases. As a whole, they tend to be poor conductors of heat and electricity and to gain electrons when they undergo chemical changes Metalloids lie along the zigzag diagonal line that divides metals and nonmetals. They show mixed properties, Several metalloids are also classified as semiconductors because of their intermediate and temperature-dependent electrical conductivity
List the characteristic properties of each group a) noble gases b) alkali metals c) alkaline earth d) halogens
Noble gases are in group 8A and are mostly unreactive. As the name implies, they are all gases in their natural state (b) Alkali metals are in group 1A and are all reactive metals (c) Alkaline earth metals are in group 2A and are also fairly reactive, (d) Halogens are in group 7A and are very reactive nonmetals
Describe the Rutherford's gold foil experiment. How did the experiment prove the plum pudding model of the atom was wrong?
Rutherford's gold foil experiment directed positively charged a particles at an ultrathin sheet of gold foil. These particles were to act as probes of the gold atoms' structures. If the gold atoms were indeed like plum pudding -with their mass and charge spread throughout the entire volume of the atom-these speeding probes should pass right through the gold foil with minimum deflection. A majority of the particles did pass directly through the foil, but some particles were deflected, and some even bounced beck. Rutherford realized that to account for the deflections, the mass and positive charge of an atom must all be concentrated in a space much smaller than the size of the atom itself
Describe Rutherford's nuclear model of the atom. What was revolutionary about his model?
Rutherford's nuclear model of the atom has three basic parts: (1) Most of the atom's mass and all of its positive charge are contained in a small core called the nucleus. (2) Most of the volume of the atom is empty space, throughout which tiny negatively charged electrons are dispersed. (3) There are as many negatively charged electrons outside the nucleus as there are positively charged particles within the nucleus. so that the atom is electrically neutral. The revolution part of this theory is the idea that matter, at its core, is much less uniform than it appears
Explain the difference between Z (the atomic number) and A (the mass number)
The atomic number, Z, is the number of protons in an atom's nucleus. The atomic mass number A is the sum of the neutrons and protons in an atom
Summarize the history of the atomic idea. How was Dalton able to convince others to accept an idea that had been controversial for 2000 years?
The first people to propose that matter was composed of small, indestructible particles were Leucippus and Democritus. These Greek philosophers theorized that matter was ultimately composed of small, indivisible particles called atomos. In the sixteenth century, modern science began to emerge. A greater emphasis on observation brought rapid advancement as the scientific method became the established way to learn about the physical world. By the early 1800s, certain observations led the English chemist John Dalton to offer convincing evidence that supported the early atomic ideas of Leucippus and Democritus. The theory that all matter is composed of atoms grew out of observations and laws. The three most important laws that led to the development and acceptance of the atomic theory were the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. John Dalton explained the laws with his atomic theory The law of conservation of mass states the following: In a chemical reaction, matter is neither created nor destroyed. In other words, when you carry out any chemical reaction, the total mass of the substances involved in the reaction does not change.
State and explain the law of definite proportions
The law of definite proportions states the following: All samples of a given compound, regardless of their source or how they were prepared, have the same proportions of their constituent elements. This means that elements composing a given compound always occur in fixed (or definite) proportions in all samples of the compound
State and explain the law of the multiple proportions. How is the law of multiple proportions different from the law of definite proportions?
The law of multiple proportions states the following: When two elements (call them A and B) form two different compounds, the masses of element B that combine with 1 g of element A can be expressed as a ratio of small whole numbers. This means that when two atoms (A and B) combine to form more than one compound, the ratio of B in one compound to B in the second compound will be a small whole number. The law of definite proportions refers to the composition of a particular compound, not to a comparison of different compounds. The law of definite proportions states that a particular compound is always made of the same elements in the same ratio.
What are the main ideas in Dalton's atomic theory? How do they help explain the laws of conservation of mass, of constant composition, and of definite proportions?
The main ideas of John D indestructible particles called atoms. (2) of a given element have the same mass dalton's atomic theory are as follows: (1) Each element is composed of tiny that distinguish them from the atoms of other elements. (3) Atoms combine in simple whole- es number ratios to form compounds. (4) Atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms change the way they are bound together with other atoms to form a new substance. The law of conservation of mass is explained by the fourth idea. Because the atoms cannot change into another element, and just change how they are bound together, the total mass will remain constant. The law of constant composition is supported by ideas 2 and 3. Because the atoms of a given element always have the same mass and other distinguishing properties, and they combine in simple whole-number ratios, different samples of the same compound will have the same properties and the same composition. The law of multiple proportions is also supported by ideas 2 and 3 because the atoms can combine in simple whole-number ratios; the ratio of the mass of B in one compound to the mass of B in a second compound will also be a small whole number.
Where do elements get their name?
The names of the elements were often given to describe their properties. I For example, argon originates from the Greek word argos, meaning "inactive." Other elements were named after figures from Greek or Roman mythology or astronomical bodies. Still others were named for the places where they were discovered or where their discoverer was born More recently, elements have been named after scientists.
What defines an element?
The number of protons in the nucleus defines the identity of an element.
State the periodic law. How did the periodic law lead to the periodic table?
The periodic law states the following: When elements are arranged in order of increasing mass, certain sets of properties recur periodically. Mendeleev organized all the known elements in a table consisting of a series of rows in which mass increased from left to right. Tho rows were arranged so that elements with similar properties were aligned in the same vertical column.
Describe the plum-pudding model of the atom
The plum-pudding model of the atom proposed by J. J. Thomson hypothesized that the negatively charged electrons were small particles electrostatically held within a positively charged sphere.
What kind of information can be determined from a mass spectrum?
The result of the mass spectrometer is the separation of the atoms in the sample according to their mass, producing a mass spectrum. The position of each peak on the x-axis gives the mass of the isotope, and the intensity (indicated by the height of the peak) gives the relative abundance of that isotope.
List the three subatomic particles that compose atoms and give the basic properties (mass and charge) of each
The three subatomic particles that compose atoms are as follo Protons, which have a mass of 1.67262 x 10 kg or 1.00727 amu and a relative charge of +1 Neutrons, which have a mass of 1.67493 x 10 kor 1.00866 amu and a relative charge of O Electrons, which have a mass of 0.00091 x 10 kg or 0.00055 amu and a relative charge of -
What is an ion? A cation? An anion?
An ion is a charged particle. Positively charged ions are called cations. Negatively charged ions are called anions.
What is atomic mass? How is it calculated?
Atomic mass represents the average mass of the isotopes that compose the element. The average calculated atomic mass is weighted according to the natural abundance of each isotope. Atomic mass(fraction of isotope n) X (mass of isotope n)
Why is the mass corresponding to a mole of one element different from the mass corresponding to a mole of another element?
Tho mass corresponding to a mole of one element is different from the mass corresponding to a mole of another cle- ment because the mass of an atom of each element is different. A mole is a specific number of atoms; so the heavier the mass of each atom, the heavier the mass of one mole of atoms
