Chapter 2 Atoms Molecules and Ions

Dalton’s atomic theories

1. Matter is composed of exceedingly small particles called atoms. An atom if the smallest unit of an element that can participate in a chemical change

2. An element consists of only one type of atom, which has a mass that is characteristic of the element and is the same for all atoms of the element, A microscopic sample of an element contains an incredibly large number of atoms, all of which have identical chemical properties

3. Atoms of one element differ in properties from atoms of all other elements

4. A compound consists of atoms of two or more elements combined in a small, whole-number ratio. In a given compound, the numbers of atoms of each of its elements are always present in the same ratio

5. Atoms are neither created nor destroyed during a chemical change, but are instead rearranged to yield substances that are different from hose present before the change.

Law of conservation of matter

Atoms are neither created nor destroyed during a chemical change, then the total mass of matter present when matter changes from one type to another will remain constant

Lat of definite proportions or law of constant composition

All samples of a pure compound contain the same elements in the same proportion by mass

Lae of multiple proportions

When two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small, whole numbers

What is a Negatively charged, subatomic particle with a mass more than one thousand-times less that of an atom

Electron

Rutherford’s two conclusions on experiments regarding positive charges

1. The volume occupied by an atom must consist of a large amount of empty space

2. A small, relatively heavy, positively charged body, the nucleus, must be at the center of each atom

Model in which an atom consists of a very small, positively charged nucleus, in which most of the mass of the atom is concentrated, surrounded by the negatively charged electrons, so that the atom is electronically neutral.

Nuclei of other elements contain the hydrogen nucleus as a “building black” this more fundamental particle is named

Proton, the positively charged, subatomic particle found in the nucleus

Isotopes

Atoms of the same element that differ in mass

They differ in mass because the have different number of neutrons, but chemically identical because they have the same number of protons

Neutrons

Uncharged, subatomic particles with a mass approximately the same as that of protons. The existence of neutron also explained isotopes

Atomic structure

The nucleus contains the majority of an atom’s mass because protons and neutrons are much heavier than electrons, whereas electrons occupy almost all of an atom’s volume. The diameter of an atom is on the order of 10^-10 m whereas the diameter of the nucleus is roughly 10^-15 m which is about 100,000 times smaller.

Unified atomic mass unit (u) (Da) (amu)

Defined as exactly 1/12 of the mass of a single atom of carbon-12 isotope and is equal to 1.6605 × 10^-24g

Fundamental unit of charge (aka elementary charge)

Magnitude of the charge of an electron (e) with e = 1.602 × 10^-19 C

Mass number (A)

Total number of protons and neutrons

Atomic number (Z)

The numbe rof protons in the nucleus of an atom

Calculating the number of neutrons

Mass number (A) - Atomic number (Z)