Chapter 2: Atoms, Molecules, and Ions

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Chapter 2 of Chemistry: The Central Science

Dalton's Atomic Theory Postulate 1

Each element is composed of extremely small particles called atoms.

Dalton's Atomic Theory Postulate 2

All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.

Dalton's Atomic Theory Postulate 3

The atoms of one element cannot be changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.

Dalton's Atomic Theory Postulate 4

Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kinds of atoms.

Atom

the smallest particles of an element that retain the chemical identity of the element.

The law of constant composition

The basis for Dalton's postulate 4; in a given compound, the relative numbers and kinds of atoms are constant.

The law of conversion of mass or the law of conservation of matter

The basis for Dalton's postulate 3; the total mass of materials present after a chemical reaction is the same as the total mass present before the reaction.

Atoms always retain their identities. In a chemical reaction, they rearrange to give new chemical combinations.

The law of multiple proportions

If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers.

Another name for cathode rays:

electrons

Based on the data Thomson collected in his experiments using cathode rays, the concept of atomic structure was modified. What were the four things that were validated by his cathode ray experiments?

-Cathode rays have mass.
-Matter contains positive and negative charge.
-Particles of the cathode rays are fundamental to all matter.
-An atom is divisible.

What is the unit of electrical charge?

coulomb

Based on the data gathered in the Rutherford's scattering experiments, the concept of atomic structure was modified. What aspects of the structure of the atom were validated by these experiments?

-the charge on the nucleus being positive
-most of the atomic volume being empty space
-the existence of the atomic nucleus
-the nuclear density being large

Based on the data gathered in Millikan's oil-drop experiments, the concept of atomic structure was modified. What aspects of the structure of the atom was validated by these experiments?

-mass of an electron
-charge on an electron

Atoms with the same atomic number but different mass numbers are called:

isotopes

An assembly of two or more atoms tightly bound together.

molecule

A molecule that is made up of two atoms.

diatomic molecule

Oxygen that exists in another molecular for is known as:

ozone, which has 3 oxygen atoms.

Compounds that are composed of molecules that contain more than one type of atom are called:

molecular compound

Chemical formulas that indicate the actual numbers and types of atoms in a molecule are called:

molecular formulas; i.e. Hydrogen Peroxide H2O2

Chemical formulas that give only the relative number of atoms of each type in a molecule are called:

empirical formulas; i.e. smallest whole number ratio of Hydrogen Peroxide is HO

This shows which atoms are attached to which within the molecule.

structural formula

If electrons are removed from or added to a neutral atom, what is formed?

ion: a charged particle

An ion with a positive charge:

cation

An ion with a negative charge:

anion

A superscript of + in a molecular formula represents:

a loss of one electron.

A superscript of - in a molecular formula represents:

a gain of one electron.

In general, metal atoms tend to (gain/lose) electrons to form cations, whereas nonmetal atoms tend to (gain/lose) electrons to form anions.

lose / gain

Ions that consist of atoms joined as in a molecule, but they have a net positive and negative charge.

polyatomic ions

Compound that contains both positively and negatively charged ions:

ionic compounds

T or F: In general, cations are metal ions.

True

T or F: In general, anions are nonmetal ions.

True

T or F: Ionic compounds are generally of metals and nonmetals, like NaCl.

True

T or F: only empirical formulas can be written for most ionic compounds.

True

When one atom completely transfers one or more electrons to another atom, resulting in the formation of ions is called:

Ionic bond

Polyatomic anions containing oxygen have names ending in -ate or -ite. What are these anions called?

oxyanions

The study of compounds of carbon is called:

organic chemistry

Compounds that contain carbon and hydrogen, often in combination with oxygen, nitrogen, or other elements are called:

organic compounds

Compounds that contain only carbon and hydrogen are called:

hydrocarbons

The most basic class of hydrocarbons where each carbon atom is bonded to four other atoms is called:

alkanes

What are the three simplest alkanes?

methane-1 carbon atom
ethane-2 carbon atoms
propane-3 carbon atoms

By replacing an H atom of an alkane with an - OH group, you get:

alcohols; add an -ol to the name:
Methanol
Ethanol
1-Propanol: 1 means it's attached to the outer C atom.

An alkane with eight carbon atoms is called:

octanes

If alkane series is extended to thousands of carbon atoms, what do you get?

polyethylene-substance used to make plastics.

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