Chapter 2 General Chemistry I

What happens when you cut a piece of graphite into smaller pieces?

You eventually yield individual carbon atoms.

What does the word 'atom' mean in Greek?

Indivisible.

Who first proposed that matter is composed of small, indestructible particles?

Leucippus and his student Democritus.

What did Democritus believe about atoms?

He believed that different kinds of atoms existed, each different in shape and size.

What is the law of conservation of mass?

In a chemical reaction, matter is neither created nor destroyed.

Who formulated the law of conservation of mass?

Antoine Lavoisier.

What is the law of definite proportions?

All samples of a given compound have the same proportions of their constituent elements.

Who is associated with the law of definite proportions?

Joseph Proust.

What does the law of multiple proportions state?

When two elements form two different compounds, the masses of one element that combine with a fixed mass of the other can be expressed as a ratio of small whole numbers.

What is an example of the law of multiple proportions?

Carbon monoxide and carbon dioxide, which have different mass ratios of oxygen to carbon.

What did John Dalton contribute to atomic theory?

He explained that each element is composed of indestructible particles called atoms and that atoms combine in simple whole-number ratios to form compounds.

What is Brownian motion?

The continuous motion of particles suspended in a fluid, confirmed by Einstein's theory.

Who tested Einstein's model of Brownian motion?

Jean Perrin.

What is the smallest identifiable unit of an element?

An atom.

How many naturally occurring elements are there?

About 91.

What did Plato and Aristotle believe about matter?

They believed matter had no smallest parts and was composed of various proportions of fire, air, earth, and water.

What is the significance of the mass of ash compared to the mass of a log after burning?

The mass of the ash is less because the matter has reacted to form gases released into the air.

What is the mass ratio of oxygen to hydrogen in water?

The decomposition of 18.0 grams of water results in 16.0 grams of oxygen and 2.0 grams of hydrogen.

What does Dalton's atomic theory state about chemical reactions?

Atoms change the way they are bound together but do not change into atoms of another element.

What did the work of Einstein and Perrin confirm?

The particulate nature of matter.

What is the relationship between the law of definite proportions and the law of multiple proportions?

The law of definite proportions states that compounds have fixed ratios, while the law of multiple proportions describes how different compounds can form from the same elements with different ratios.

What is the mass ratio of nitrogen to hydrogen in ammonia?

The mass ratio can be calculated based on the given mass of hydrogen.

What is the implication of the law of conservation of mass in chemical reactions?

The total mass of substances involved does not change during a reaction.

What is the significance of the ratio of masses in the law of multiple proportions?

It shows that the ratios can be expressed as small whole numbers.

What did Democritus state about existence?

He stated that nothing exists except atoms and empty space.

What is the role of atoms in connecting macroscopic and microscopic worlds?

Atoms are the key to understanding the composition and behavior of matter.

How did early atomic theories influence modern chemistry?

They laid the groundwork for the development of atomic theory and the understanding of chemical reactions.

What does the law of definite proportions state?

It applies to two or more samples of the same compound.

Who discovered the electron?

J. J. Thomson

What apparatus did J. J. Thomson use to discover the electron?

A cathode ray tube

What are the properties of cathode rays discovered by Thomson?

They travel in straight lines, are independent of the material of the cathode, and carry a negative charge.

What was the charge-to-mass ratio measured by Thomson?

Coulombs (C) per gram.

What experiment did Robert Millikan conduct?

The oil drop experiment.

What did Millikan's oil drop experiment measure?

The charge of a single electron.

What is the relationship between the charge of Millikan's oil drops and the charge of a single electron?

The charge on any drop was always a whole-number multiple of the charge of a single electron.

What model of the atom did J. J. Thomson propose?

The plum-pudding model.

What was the unexpected result of Rutherford's gold foil experiment?

Some alpha particles were deflected, and some bounced back.

What conclusion did Rutherford draw from his gold foil experiment?

Matter contains large regions of empty space with small regions of dense matter.

What is the nuclear theory of the atom proposed by Rutherford?

1) Most of the atom's mass and all positive charge are in the nucleus; 2) Most of the atom is empty space; 3) There are as many electrons outside the nucleus as protons inside.

What particles were discovered to account for the missing mass in Rutherford's model?

Neutrons.

What is the mass comparison between protons and neutrons?

Neutrons have a similar mass to protons but no charge.

What are the three subatomic particles that compose all atoms?

Protons, neutrons, and electrons.

What defines the identity of an element?

The number of protons in its nucleus.

What is the atomic number represented by?

The number of protons in an atom's nucleus, symbolized as Z.

How is each element identified on the periodic table?

By a unique atomic number and a unique chemical symbol.

What is the chemical symbol for helium?

He.

What is the chemical symbol for carbon?

C.

What is the chemical symbol for nitrogen?

N.

Which element contains 50 protons in its nucleus?

Tin.

What is the mass of a proton compared to an electron?

A proton is significantly more massive than an electron.

What is the charge of a neutron?

A neutron has no charge.

What is the significance of the atomic number?

It determines the element's identity and its position on the periodic table.

What did Rutherford's experiment reveal about the structure of the atom?

It revealed that atoms have a dense nucleus surrounded by empty space.

What is the role of electrons in an atom?

Electrons are negatively charged particles that orbit the nucleus.

What are isotopes?

Atoms with the same number of protons but a different number of neutrons.

What is the mass number of an isotope?

The sum of the number of protons and neutrons in an atom.

How is the mass number represented?

By the symbol A.

What does the atomic number Z represent?

The number of protons in an atom's nucleus.

What notation is used for isotopes?

The chemical symbol followed by a dash and the mass number (e.g., Ne-20).

What is the natural abundance of isotopes?

The relative amount of each isotope in a naturally occurring sample of an element.

What are cations?

Positively charged ions formed by losing electrons.

What are anions?

Negatively charged ions formed by gaining electrons.

What is the periodic law?

When elements are arranged by increasing mass, certain properties recur periodically.

Who is credited with the periodic law?

Dmitri Mendeleev.

What did Mendeleev's periodic table allow him to do?

Predict the existence and properties of undiscovered elements.

What is the modern periodic table organized by?

Increasing atomic number.

How are elements classified in the periodic table?

As metals, nonmetals, and metalloids.

What are common properties of metals?

Good conductors of heat and electricity, malleable, ductile, and shiny.

Where are nonmetals located on the periodic table?

On the upper-right side.

What are common properties of nonmetals?

Poor conductors of heat and electricity, not ductile or malleable, and tend to gain electrons.

What are metalloids?

Elements that exhibit mixed properties and are often semiconductors.

What is the total number of groups in the periodic table?

18 groups.

What is the total number of periods in the periodic table?

7 periods.

What is the significance of the zigzag line in the periodic table?

It divides metals and nonmetals.

What are transition metals?

Elements whose properties are less predictable based on their position in the periodic table.

What is the difference between main-group elements and transition elements?

Main-group elements have predictable properties, while transition elements do not.

How many neutrons does an argon isotope with a mass number of 40 contain?

22 neutrons (40 protons - 18 protons = 22 neutrons).

What is the natural abundance of carbon-12?

98.93%.

What is the natural abundance of carbon-13?

1.07%.

What are the main-group elements in the periodic table?

Elements in columns labeled with a number and the letter A (1A-8A or groups 1, 2, and 13-18).

What are transition elements in the periodic table?

Elements in columns labeled with a number and the letter B (or groups 3-12).

What are noble gases?

Group 8A elements that are mostly unreactive, including helium, neon, argon, krypton, and xenon.

What is a characteristic of helium?

Helium is chemically stable and does not combine with other elements to form compounds.

What are alkali metals?

Group 1A elements that are all reactive metals, including lithium, sodium, potassium, and rubidium.

What are alkaline earth metals?

Group 2A elements that are fairly reactive but not as reactive as alkali metals, including calcium and magnesium.

What are halogens?

Group 7A elements that are very reactive nonmetals, including fluorine, chlorine, bromine, and iodine.

What happens to a main-group metal in terms of electrons?

It tends to lose electrons, forming a cation with the same number of electrons as the nearest noble gas.

What happens to a main-group nonmetal in terms of electrons?

It tends to gain electrons, forming an anion with the same number of electrons as the nearest noble gas.

How do alkali metals typically form ions?

They tend to lose one electron and form 1+ ions.

How do alkaline earth metals typically form ions?

They tend to lose two electrons and form 2+ ions.

How do halogens typically form ions?

They tend to gain one electron and form 1- ions.

What is atomic mass?

The average mass of an element's isotopes, weighted according to their natural abundance.

What is the atomic mass of chlorine based on its isotopes?

The atomic mass of chlorine is approximately 35.45 amu, calculated from its isotopes.

What is Avogadro's number?

The number of particles in one mole, approximately 6.022 x 10^23.

What is a mole in chemistry?

A unit that measures the amount of substance, equivalent to Avogadro's number of particles.

How is the molar mass of an element defined?

The mass of 1 mole of atoms of that element, numerically equal to its atomic mass in grams per mole.

What is the relationship between atomic mass and molar mass?

The molar mass in grams per mole is numerically equal to the atomic mass in atomic mass units (amu).

What is the conceptual plan for counting atoms by weighing?

Obtain the mass of the sample, convert it to moles using molar mass, then convert to the number of atoms using Avogadro's number.

What is the significance of the atomic mass of carbon?

Carbon has two isotopes, C-12 and C-13, with the atomic mass closest to 12.00 amu.

What is the average atomic mass of carbon based on its isotopes?

The average atomic mass of carbon is approximately 12.01 amu.