general chemistry: chapter 2

What are the four postulates of John Dalton's atomic theory?

1: Each element is composed of extremely small particles called atoms.

2: All atoms composed of a given element are identical, but the atoms of one element are different from the atoms of all other elements.

3: 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.

4: Compounds are fomed when atoms of more than one element combine; a given compound alwats has the same relative number and kind of atoms.

What is the law of constant composition?

in a given compound, the relative numbers and kinds of atoms are constant.

What is the law of conservation of mass?

The total mass of materials present after a chemical reaction is the same as the total mass present before the reaction.

What is 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.

What are subatomic particles?

- Protons

- Neutrons

- Electrons

What are the electrical charges that compose an atom?

The atom is composed in part of electrically charged particles, some with a positive charge and some with a negative charge.

What is the relationship between similarly charged particles?

They repel each other.

What is the relationship between oppositely charged particles?

They attact each other.

What are cathode rays?

- When a high voltage was applied to the electrodes in the tube, radiation was produced between the electrodes.

- This radiation originated at the negative electrode and traveled to the positive electrode.

- They were detected since they caused certain materials to

fluoresce.

- Always the same.

What is fluorescence?

To give off light.

How are cathode rays and electrons related?

Cathode rays as streams of negatively charged particles are called electrons.

What is the mass of an electron?

9.10938 x 10^-28 g

What is radioactivity?

Spontaneous emission of radiation.

What are the three types of radiation?

- Alpha

- Beta

- Gamma

What are the paths of alpha and beta radiation when affected by electrcal fields?

The paths of alpha and beta radiation are bent by an electric field, although in opposite directions.

What are the paths of gamma radiation when affected by electrcal fields?

Unnafectted, the same path.

What do alpha and beta rays consist of?

Fast-moving electrically charged particles.

Why are beta ray particles considered the radioactive equivalent of cathode rays?

Beta particles are nothing more than high-sped electrons that can be considered the radioactive equivilent of cathode rays.

What is the electron charge of each ray?

- Alpha rays: 1-

- Beta rays: 2+

- Gamma rays: does not consist of particles and carries no charge.

What is the nucleus of an atom?

- Extremely dense region of the atom.

- Contains neutrons and protons.

What are protons?

Positive particles.

What are neutrons?

Neutral particles.

What is the charge of an electron?

-1.602 x 10^-19 C

What is the charge of an proton?

1.602 x 10^-19 C

How are atoms neutrally charged?

They have an equal number or electrons and protons so they're neutral.

What is an angstrom?

The non-SI unit of length used for atomic dimensions.

What are electrons attracted to?

Protons in the nucleus due to the electrostatic force that exists between partticles of opposite electrical charges.

What is the atomic mass unit equal to in grams?

1 amu = 1.66054 x 10^-24 g

What is the amu of the 3 subatomic particles within an atom?

- Proton: 1.0073 amu

- Neutron: 1.0087amu

- Electron: 5.486 x10^-4 amu

What is the diameter of an atomic nucleus?

10^-4 A.

What is different about every atom?

Its number of protons.

What is the atomic number?

The number of protons in an atom.

What are the four basic forces in nature?

- Gravitational

- Electromagnetic

- Strong nuclear

- Weak nuclear

What are gravitational forces?

Attractive forces that act between all objects in proportion to their masses.

What are electromagnetic forces?

Attractive or repulsive forces that act between either electrically charged or magnetic forces.

How is the magnitude of electric forces between two charged particles found?

- Coulomb's law: F = kQ₁Q₂/d₂

- Q₁Q₂ = the magnitudes of the charges on the two particles

- d = the distance between their centers

- k = the constant determined by the units for Q and d

What does a negative value for force indicate?

Attraction.

What does a positive value for force indicate?

Repulsion.

What is strong nuclear force?

- Strong only when particles are extremely close together, as are the protons and neutrons in an atomic nucleus.

- Stronger than the gravitational force.

What is weak nuclear force?

Weaker than the electric force.

What is the mass number?

Total number of protons and neutrons in an atom.

What are isotopes?

- Atoms with identical atomic numbers but different mass numbers.

- Same number of protons, different number of neutrons

What is atomic weight?

Average atomic mass of an element.

How can somone find atomic weight?

Ε[(isotope mass) x (fractional isotope abundance)]

When was the periodic table developed?

1869

What is the periodic table?

The arrangements of elements in order of increasing atomic number, with elements having similar properties placed in vertical column.

What are periods?

The horizontal rows on the periodic table.

What are groups on the periodic table?

The vertical columns.

What is a diatomic molecule?

A molecule made up of two atoms.

What are molecular compounds?

Compounds composed of molecules contain more than one type of atom.

What are molecular formulas?

Chemical formulas that indicate the actual numbers of atoms in a molecule.

What are empirical formulas?

Chemical formulas that give only the relative number of atoms of each type in a molecule.

What is a structural formula?

The atoms are represented by their chemical symbols, and lines are used to represent the bonds that hold the atoms together.

What are the different representations of a molecules?

- Perspective drawings

- Ball-and-stick models

- Space-filling models

What are perspective drawings?

- Perspective drawings use wedges and dashed lines to depict bonds that are not in the plane of the paper.

- This gives a crude sense of the three-dimensional shape

of a molecule.

What are ball and stick models?

- Ball-and-stick models show atoms as spheres and bonds as sticks.

- This type of model has the advantage of accurately representing the angles at which the atoms are attached to one another in a molecule.

- Sometimes the chemical symbols of the elements are superimposed on the balls, but often the atoms are identified simply by color.

What are space-filling models?

- Space-filling models depict what a molecule would look like if the atoms were scaled up in size.

- These models show the relative sizes of the atoms,

but the angles between atoms, which help define their molecular geometry, are often more difficult to see than in ball-and-stick models.

- Because space-filling models give a good representation of the true size of a molecule, they are useful for picturing how two molecules might fit together or pack in the solid state.

- As with ball-and-stick models, the identities of the atoms are typically indicated by color

What is an ion?

If electrons are removed or added to an atom it is now charged.

What is a cation?

Ion with a positive charge.

What is a anion?

Ion with a negative charge.

What is the net charge of an ion represented by?

Positive: Superscripts, + , 2+, 3+ : Loss of such electrons

Negative: -, 2-, 3- : Gain of such electrons

What are polyatomic ions?

Atoms join as in a molecule but carry a net positive or negative charge.

What is an ionic compound?

A compound that consists of cations and anions.

What are chemical nomenclature?

The system used in naming substances.

What are organic compounds?

Contain carbon and hydrogen, often in combination with oxygen, nitrogen or other elements.

What are inorganic compounds?

Do not contain carbon and hydrogen, or in combination with oxygen, nitrogen or other elements.

What are transition metals?

Metals that form cations with different charges and elements that occur in the middle of the periodic table.

What is an acid?

- A substance whose molecules yield hydrogen ions when dissolved in water.

- An acid is composed of an anion connected to enough H⁺ ions to neutralize or balance the anion's charge.

What is organic chemistry?

The study of carbon compounds.

What are hydrocarbons?

Compounds that only contain carbon and hydrogen.

What are alkanes?

Hydrocarbons bonded to four other atoms.

What are functional groups?

Specfifc groups of atoms.

Whatare isomers?

Compounds with the same molecular formula but different arrangemnets of atoms.

What are structural isomers?

Compounds that have the same molecular formula but different structural formulas.

What are the different ways to name acids?

- Acids containing anions whose names end in -ide are named by changing the -ide ending to -ic, adding the prefix hydro- to this anion name, and then following with the word acid.

- Acids containing anions whose names end in -ate or -ite are named by changing -ate to -ic and -ite to-ous and then adding the word acid. Prefixes in the anion name are retained in the name of the acid.