Vocab

Law of definite proportions

Different samples of the same compound always contain its constituent elements in the same proportions by mass.

Law of multiple Proportions

If two elements can combine to form more than one type of compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers.

Law of conservation of mass

Hypothesis stating that matter can be neither created nor destroyed.

Atom

The basic unit of an element that can enter into chemical combination.

Radiation

The emission and transmission of energy through space in the form of particles and/or waves.

Electrons

A subatomic particle that has a very low mass and carries a single negative electric charge.

Radioactivity

The spontaneous breakdown of an atom by emission of particles and/or radiation.

alpha (α) rays/ alpha particles

Helium ions with a positive charge of +2.

beta (β) rays/beta particles

electrons

gamma (γ) rays

High-energy radiation

Nucleus

The central core of an atom

Protons

A subatomic particle having a single positive electric charge. The mass of a proton is about 1840 times that of an electron.

Neutrons

A subatomic particle that bears no net electric charge. Its mass is slightly greater than a proton’s mass.

Atomic number (Z)

The number of protons in the nucleus of an atom.

Mass number (A)

The total number of neutrons and protons present in the nucleus of an atom.

Isotopes

Atoms having the same atomic number but different mass numbers.

Periodic table

A tabular arrangement of the elements.

period

A horizontal row of the periodic table.

Group/Families

The elements in a vertical column of the periodic table.

Metal

Elements that are good conductors of heat and electricity and have the tendency to form positive ions in ionic compounds.

Nonmetals

Elements that are usually poor conductors of heat and electricity.

Metalloid

An element with properties intermediate between those of metals and nonmetals.

Alkali Metals

The Group 1 elements (Li, Na, K, Rb, Cs, and Fr).

Alkaline Earth Metals

The Group 2 elements (Be, Mg, Ca, Sr, Ba, and Ra).

Halogens

The nonmetallic elements in Group 17 (F, Cl, Br, I, and At).

Noble gases

Nonmetallic elements in Group 18 (He, Ne, Ar, Kr, Xe, and Rn).

Molecule

An aggregate of at least two atoms in a definite arrangement held together by special forces.

Diatomic molecule

A molecule that consists of two atoms.

Polyatomic molecule

A molecule that consists of more than two atoms.

Ion

An atom or a group of atoms that has a net positive or negative charge.

Cation

An ion with a net positive charge.

Anion

An ion with a net negative charge

Ionic compound

Any neutral compound containing cations and anions.

Monatomic Ion

An ion that contains only one atom.

Polyatomic Ion

AN ion that contains more than one atom

Chemical Formula

An expression showing the chemical composition of a compound in terms of the symbols for the atoms of the elements involved.

Molecular formula

An expression showing the exact numbers of atoms of each element in a molecule.

Allotrope

Two or more forms of the same element that differ significantly in chemical and physical properties.

Structural Formula

A chemical formula that shows how atoms are bonded to one another in a molecule.

Empirical formula

An expression showing the types of elements present and the simplest ratios of the different kinds of atoms.

Organic Compound

Compounds that contain carbon, usually in combination with elements such as hydrogen, oxygen, nitrogen, and sulfur.

Inorganic compounds

Compounds other than organic compound

Binary Compounds

Compounds formed from just two elements.

ternary compounds

Compounds consisting of three elements.

Acid

A substance that yields hydrogen ions (H⁺) when dissolved in water.

Oxoacids

An acid containing hydrogen, oxygen, and another element (the central element).

Oxoanions

An anion derived from an oxoacid

Hydrates

Compounds that have a specific number of water molecules attached to them.