CH. 2: Subatomic Structure

Question 1

Law of Conservation of Mass

Answer 1

Antoine Lavoisier, 1789

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

When a chemical reaction occurs, the total mass of the substances involved in the reaction does not change.

Question 2

Law of Definite Proportions

Answer 2

Joseph Proust,1797

The elements composing a given compound always occur in fixed (or definite) proportions in all samples of the compound.

Also called the “Law of Constant Composition”

Mass ratio = 16.0g O / 2.0g H = 8.0 or 8:1
Thus, any sample of pure water will have a ratio of 8 grams of oxygen per every 1 gram of hydrogen.

Question 3

Law of Multiple Proportions

Answer 3

John Dalton, 1804

When two elements (A, B) form two different compounds, the masses of element B that combine with 1g of element A can be expressed as a ratio of small whole numbers.

The law of multiple proportions is important because it provides fundamental insights into how elements combine to form compounds, which is essential for understanding a wide range of chemical phenomena and for making predictions in chemical reactions.

Question 4

Atomic Theory

Answer 4

John Dalton, 1808

1. Each element is composed of tiny, indestructible particles called atoms. (later disproven)
2. All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements.
3. Atoms combine in simple, whole-number ratios to form compounds.
4. Atoms of one element cannot change into atoms of another element. In a chemical reaction, atoms can only change the way that they are bound together.

Question 5

Atomic number (Z)

Answer 5

The number of protons in the nucleus of every atom of that element.

Question 6

Isotope

Answer 6

An atom with the same number of protons but a different number of neutrons.

Question 7

Natural abundance

Answer 7

The relative percentage of a particular isotope in a naturally occurring sample with respect to other isotopes of the element.

Question 8

Mass number (A)

Answer 8

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

Question 9

Proton

Answer 9

A positively charged subatomic particle found in the nucleus of an atom.

Approx. 1 amu

Question 10

Atomic mass

Answer 10

The average relative mass of an element in relation to the % abundance of each of the element’s isotopes and their number of neutrons.

Question 11

atomic mass unit (amu)

Answer 11

1/12th the mass of a carbon atom that contains six protons and six neutrons (carbon-12). The mass of a proton or neutron is approximately 1 amu.

The carbon-12 isotope is used because it is precise, naturally abundant, and stable- it does not undergo radioactive decay.

Question 12

radioactivity

Answer 12

the emission of small energetic particles from the core of certain unstable atoms.

Question 13

nucleus

Answer 13

small core of an individual atom, which contains the protons and neutrons (most of its mass), as well as its positive charge. Most of the volume of an atom is empty space.

Question 14

Neutron

Answer 14

A neutral particle within the nucleus.

Approx. 1 amu