Chemistry Chapter 2: Atoms and Molecules

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Questions and Answers

What defines a molecular compound?

It contains only metals.

It consists of ions.

It contains molecules and almost always only nonmetals. (correct)

It has only one type of atom.

Which of the following elements exists as diatomic molecules at room temperature?

Carbon

Argon

Chlorine (correct)

Carbondioxide

What is the difference between empirical and molecular formulas?

Molecular formulas give the exact number of atoms of each element. (correct)

Empirical formulas show the order of attachment of atoms.

Molecular formulas give the lowest whole-number ratio of atoms.

Empirical formulas provide exact numbers while molecular do not.

What did Democritus propose about the smallest particle in nature?

It is called 'atomos'. Signup and view all the answers

What is the charge of the chromate ion?

2− Signup and view all the answers

Which scientist is credited with the Law of Conservation of Mass?

Antoine Lavoisier Signup and view all the answers

How would you write the formula for the sulfate ion?

SO4 2− Signup and view all the answers

How are cations formed?

By losing electrons. Signup and view all the answers

According to the Law of Constant Composition, what can be said about the relative number of atoms in a compound?

It remains the same in any sample of the compound. Signup and view all the answers

Which statement about naming cations is correct?

If a cation has multiple charges, the charge is indicated using Roman numerals. Signup and view all the answers

What type of compound is NaCl classified as?

Ionic compound Signup and view all the answers

What does the Law of Multiple Proportions state about two elements forming compounds?

The masses of one element that combines with a fixed mass of another are in small whole number ratios. Signup and view all the answers

Which of the following is a polyatomic cation?

NH4+ Signup and view all the answers

Which of the following is true about metalloids?

They can have properties of both metals and nonmetals. Signup and view all the answers

Which of the following is NOT one of Dalton's postulates regarding atoms?

Atoms can be created or destroyed in reactions. Signup and view all the answers

What is the chemical formula for the peroxide ion?

O2 2− Signup and view all the answers

Which of these elements is an exception to the rules for metalloids?

Aluminum Signup and view all the answers

What is the charge on the nitride ion?

3− Signup and view all the answers

What do structural formulas represent?

The order in which atoms are attached. Signup and view all the answers

Which law discovered by Joseph Proust emphasizes a compound's definite composition?

Law of Constant Composition Signup and view all the answers

What distinguishes the atoms of one element from those of all other elements according to Dalton's atomic theory?

They have different masses and properties. Signup and view all the answers

How would the formula for a compound containing ammonium and nitrate be written?

NH4NO3 Signup and view all the answers

In the context of the atomic theory, what does 'atomos' mean?

Indivisible Signup and view all the answers

Which of the following ions has a 2− charge?

Sulfide Signup and view all the answers

What suffix do polyatomic cations typically end with?

-ium Signup and view all the answers

Which ion is correctly associated with the oxoanion naming convention?

PO4 3−: phosphate Signup and view all the answers

How would you name HCl according to the nomenclature rules for inorganic acids?

Hydrochloric acid Signup and view all the answers

What is the correct name for CIO4−?

Perchlorate Signup and view all the answers

What prefix is used to denote a compound with two atoms of an element in molecular nomenclature?

di- Signup and view all the answers

What is the relation between the number of oxygens and the suffixes -ite and -ate in oxyanion nomenclature?

-ate indicates more oxygens than -ite Signup and view all the answers

What is the correct naming for the ion CIO2−?

Chlorite Signup and view all the answers

What change occurs in the nomenclature when the anion's name ends in -ate?

Change to -ic acid Signup and view all the answers

What is the charge of the magnesium ion?

2+ Signup and view all the answers

Which ion is also known as cobalt(II) or cobaltous ion?

Co2+ Signup and view all the answers

Which ion has the formula Sn2+?

Tin(II) or stannous ion Signup and view all the answers

What is the common name for the ion with the formula Cu2+?

Copper(II) or cupric ion Signup and view all the answers

Which of the following is the charge of the iron(II) or ferrous ion?

2+ Signup and view all the answers

Identify the ion that is referred to as mercury(I) or mercurous ion.

Hg22+ Signup and view all the answers

Which name corresponds to the ion with the formula Ni2+?

Nickel(II) or nickelous ion Signup and view all the answers

What is the common name for the lead(II) or plumbous ion?

Pb2+ Signup and view all the answers

Which of the following ions is known as barium ion?

Ba2+ Signup and view all the answers

What was the primary issue with the plum pudding model proposed by J.J. Thomson?

It could not explain the deflection of alpha particles. Signup and view all the answers

What did Rutherford's gold foil experiment demonstrate?

Most of an atom's mass is concentrated in a small nucleus. Signup and view all the answers

Which of the following accurately describes a proton?

It has a positive charge and contributes significantly to atomic mass. Signup and view all the answers

How is the atomic number of an element defined?

It is the number of protons in the nucleus. Signup and view all the answers

In the modern view of atomic structure, most of the atom is considered to be:

Empty space. Signup and view all the answers

What is the relative mass of an electron compared to protons and neutrons?

Negligible compared to protons and neutrons. Signup and view all the answers

Which subatomic particle has a charge of +1?

Proton Signup and view all the answers

What conclusion did Rutherford draw from his scattering experiment?

A small, dense nucleus exists at the center of the atom. Signup and view all the answers

What is the main conclusion of Rutherford's gold foil experiment?

Atoms are composed mostly of empty space. Signup and view all the answers

Which of the following illustrates a physical reaction?

Ice melting into water. Signup and view all the answers

Which statement is true regarding isotopes?

Isotopes of an element have different mass numbers. Signup and view all the answers

Which metric prefix represents one million?

Mega- Signup and view all the answers

Which of the following best describes 'accuracy' in scientific measurements?

The closeness of a measurement to the true value. Signup and view all the answers

Study Notes

Chapter 2: Atoms, Molecules, and Ions

This chapter introduces the fundamental concepts of atoms, molecules, and ions.
It covers atomic theory, the discovery of subatomic particles, and the structure of the atom.
It also explains the periodic table and different types of chemical formulas.
Lastly, it discusses molecules and molecular compounds.

2.1 Atomic Theory of Matter

Some ancient Greek philosophers proposed the existence of indivisible particles called "atomos."
Experiments in the 18th and 19th centuries led to the development of atomic theory by John Dalton.
The theory is based on several laws: the law of constant composition, the law of conservation of mass, and the law of multiple proportions.
The law of constant composition states that compounds have a fixed and predictable elemental composition in any sample. Examples include H₂O, CO, and CO₂.
The law of conservation of mass states that the total mass of substances remains constant throughout a chemical process.
The law of multiple proportions states that if two elements form more than one compound, the masses of one element that combine with a constant mass of the other element are in a ratio of small whole numbers.

Postulates of Dalton's Atomic Theory

Each element is composed of tiny, indivisible particles called atoms.
All atoms of a given element are identical in mass and properties.
Atoms of different elements have different masses and properties.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
Atoms are neither created nor destroyed in chemical reactions. These atoms rearrange and recombine.

2.2 Discovery of Subatomic Particles

Dalton's atomic model saw the atom as the ultimate fundamental particle.
Discoveries of electrons, radioactivity, the nucleus, protons, and neutrons showed the atom has internal structure.
J.J. Thomson's cathode ray experiments led to the discovery of the electron.
Thomson's experiments measured the charge-to-mass ratio of the electron (1.76×10⁸ coulombs/gram.).
Robert Millikan's oil-drop experiment established the electron's charge (1.602×10⁻¹⁹C).
Rutherford's gold foil experiment established the nuclear structure of the atom.

2.3 Modern View of Atomic Structure

The modern view of the atom describes it as mostly empty space.
The atom contains a tiny, dense, positively charged nucleus.
The nucleus is surrounded by negatively charged electrons.
Other subatomic particles, like protons and neutrons, compose the atom.
Atoms are very small (1-5 Å or 100-500 pm).
The nucleus is extremely small with a radius that is about 10⁻⁴ Å to 1-5 Å.

Subatomic Particles

Protons and electrons have a charge; neutrons are neutral.
Protons and neutrons have almost the same mass (relative mass 1); an electron is significantly lighter.(relative mass 0).

Atomic Number

The atomic number is the number of protons in the nucleus of an atom.
In a neutral atom, the number of protons equals the number of electrons.

Atoms of an Element

Elements are represented by symbols (e.g., C for carbon).
The atomic number (number of protons) is written as a subscript.
The mass number (number of protons + neutrons) is written as a superscript. Example: ¹²₆C

Isotopes

Atoms of the same element can have different numbers of neutrons, forming isotopes.
Isotopes have different mass numbers but the same atomic number. Example: isotopes of Carbon shown in table 2.2, including ¹¹C, ¹²C, ¹³C, and ¹⁴C.

2.4 Atomic Mass Unit (amu)

The atomic mass unit (amu) is used to measure the masses of atoms.
It is defined relative to the mass of carbon-12 (1 amu = 1.66054 ×10⁻²⁴ g).
The mass of an atom is determined by the relative contributions of its protons, neutrons, and electrons.

Atomic Weight

Atomic weight is the average mass of all the naturally occurring isotopes of an element, weighted by their relative abundances.
The atomic weight of an element is determined experimentally using mass spectrometry.

2.5 Periodic Table

The periodic table arranges elements in order of increasing atomic number.
Elements in the same column (group) have similar chemical properties.
Elements in the same row (period) show recurring trends in chemical and physical properties.
Metals are on the left side of the periodic table, while nonmetals are on the right side. Metalloids are located between metals and nonmetals.

Reading the Periodic Table

Atomic numbers are listed above the symbol for each element.
Atomic weights are listed below the symbol.

2.6 Molecules and Molecular Compounds

A chemical formula uses subscripts to denote the number of atoms of each element in a molecule.
Some elements exist as diatomic molecules. Examples, such as H₂, O₂, N₂, etc.
Molecular compounds are composed of molecules containing only nonmetals.

Diatomic Molecules

Seven elements exist naturally as diatomic molecules containing two atoms.
These elements include Hydrogen(H₂), Nitrogen(N₂), Oxygen(O₂), Fluorine(F₂), Chlorine(Cl₂), Bromine(Br₂) and Iodine(I₂).

Types of Formulas

Empirical formulas represent the lowest whole-number ratio of atoms in a compound.
Molecular formulas represent the exact number of atoms in a molecule of a compound.

Picturing Molecules

Structural formulas show the order in which atoms are attached in a molecule.
Ball-and-stick, space-filling models, and perspective drawings depict the three-dimensional arrangement of atoms.

2.7 Ions and Ionic Compounds

Ions are formed when atoms gain or lose electrons.
Cations are positively charged ions formed by losing electrons.
Anions are negatively charged ions formed by gaining electrons.
Ionic compounds are formed between metals and nonmetals.
This occurs through electron transfer from a metal to a nonmetal, creating oppositely charged ions.

2.8 Naming Inorganic Compounds

The system of naming inorganic compounds is called chemical nomenclature.

Common Cations

Cations are positively charged ions.
Specific examples of common cations, including H⁺, Li⁺, Na⁺, K⁺, Cs⁺, Ag⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Zn²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Mn²⁺, Hg²⁺, Hg₂²⁺, Ni²⁺, Pb²⁺, and Sn²⁺.

Common Anions

Anions are negatively charged ions.
Specific examples of common anions, including H⁻, F⁻, Cl⁻, Br⁻, I⁻, CN⁻, OH⁻, O²⁻, O₂²⁻, S²⁻, N³⁻, CO₃²⁻, CrO₄²⁻, Cr₂O₇²⁻, SO₄²⁻, and PO₄³⁻.

Polyatomic Ions

Polyatomic ions are groups of atoms with an overall charge. Examples include NH₄⁺ and SO₄²⁻.

Writing Inorganic Formulas

The charges on cations and anions determine the subscripts in the formula for ionic compounds.
The formula must be electrically neutral.

Naming Inorganic Compounds

Cations are named before anions.
Transition metals require Roman numerals to represent their charges.
Polyatomic ions have specific names.
Specific rules for naming various types of ionic compound.

Patterns in Oxyanion Nomenclature

Oxyanions contain oxygen and another element.
The charge and number of oxygens influence the naming pattern.
Different numbers of oxygens dictate different suffixes (e.g., -ite for fewer oxygens and -ate for more).

Inorganic Acid Nomenclature

Acids contain hydrogen and an anion.
Naming depends on the ending of the anion.

Nomenclature of Binary Molecular Compounds

Binary molecular compounds are formed between nonmetals.
The naming includes prefixes denoting the number of atoms of each element (e.g., mono-, di-, tri-, tetra-, penta-, etc.).

2.9 Some Simple Organic Compounds

Organic Chemistry focuses on compounds containing carbon.
Naming follows a specific system.
Hydrocarbon names follow a pattern related to the number of carbon atoms (e.g., meth-, eth-, prop-, etc.).
The ending is followed by -ane. Example: Methane, Ethane, Propane.

Nomenclature of Alcohols

When a hydrogen in an alkane is replaced with something else (a functional group, like -OH in alcohols), the name is derived from the name of the alkane.
The ending denotes the type of compound.
Alcohols end in -ol.

Nomenclature Isomers: Alcohols

When two or more molecules have the same chemical formula but different structures, they are called isomers.
1-propanol and 2-propanol are isomers
They differ in the placement of the hydroxyl (-OH) group on the carbon chain.

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Explore the foundational concepts of atoms, molecules, and ions in this chapter quiz. Delve into atomic theory, the discovery of subatomic particles, and the structure of the atom. You'll also learn about the periodic table and various chemical formulas, setting the stage for understanding molecular compounds.