Ch.2- Atoms, ions, and Molecules: The Building Blocks of Matter

subatomic particles

The neutrons, protons, and electrons in an atom.

cathode rays

Streams of electrons emitted by the cathode in a partially evacuated tube.

electron

A subatomic particle that has a negative charge and negligible mass.

radioactivity

The spontaneous emission of high-energy radiation and particles by materials.

beta (β) particle

A particle that is emitted during radioactive decay and is equivalent in mass and charge to a high-energy electron.

alpha (α) particle

A particle that is emitted during radioactive decay and is equivalent in mass and charge to a ⁴He nucleus.

nucleus of an atom

The positively charged center of an atom that contains nearly all the atom's mass.

proton

A subatomic particle in the nuclei of atoms that has a positive charge and a mass number of 1.

neutron

An electrically neutral (uncharged) subatomic particle with a mass number of 1.

unified atomic mass unit (u)

The unit used to express the relative masses of atoms and subatomic particles; it is exactly 1/12 the mass of 1 atom of carbon with 6 protons and 6 neutrons in its nucleus.

dalton Da

A unit of mass equal to 1 unified atomic mass unit.

isotopes

Atoms of an element containing the same number of protons but different numbers of neutrons.

nuclide

A specific isotope of an element.

atomic number (Z)

The number of protons in the nucleus of an atom.

mass number (A)

The number of nucleons in an atom.

nucleon

A proton or neutron in a nucleus.

periodic table of elements

A chart of the elements in order of their atomic numbers and in a pattern based on their physical and chemical properties.

period of elements

All the elements in a row of the periodic table.

group or family of elements

All the elements in a column of the periodic table.

metals

Elements that are typically shiny, malleable, ductile solids that conduct heat and electricity well and tend to form positive ions.

nonmetals

Elements with properties opposite those of metals, including poor conductivity of heat and electricity.

metalloids

Elements that tend to have physical properties of metals but chemical properties of nonmetals.

main group elements or representative elements

The elements in groups 1, 2, and 13–18 of the periodic table.

transition metals

The elements in groups 3–12 of the periodic table.

noble gases

cation

A positively charged ion.

anion

A negatively charged ion.

radionuclide

A radioactive (unstable) nuclide.

alkali metal

An element in group 1 of the periodic table.

halogen

An element in group 17 of the periodic table.

alkaline earth metal

An element in group 2 of the periodic table.

chalcogen

An element in group 16 of the periodic table.

average atomic mass

The weighted average of the masses of all isotopes of an element, calculated by multiplying the natural abundance of each isotope by its mass in unified atomic mass units and then summing the products.

natural abundance

The proportion of a particular isotope, usually expressed as a percentage, relative to all the isotopes of that element in a natural sample.

mass spectrometer

An analytical instrument for determining the chemical composition of samples by ionizing them and then separating the ions based on their mass (m) to charge (z) ratios.

molecular mass

The mass in unified atomic mass units of one molecule of a molecular compound.

formula unit

The smallest electrically neutral unit of an ionic compound.

formula mass

The mass in unified atomic mass units of one formula unit of an ionic compound.

mole (mol)

An amount of a substance that contains a number of particles (atoms, ions, molecules, or formula units) equal to the Avogadro constant.

Avogadro constant (N_A)

The number of elementary entities—atoms, ions, or molecules—in 1 mole of a substance. The exact value of the constant is 6.02214076 × 10 ²³ mol ^_1 .

molar mass (M)

The mass of 1 mole of a substance.

molecular ion M⁺

An ion formed in a mass spectrometer when a molecule loses an electron after being bombarded with high-energy electrons. The molecular ion has a charge of 1+ and has essentially the same molecular mass as the molecule from which it came.

mass spectrum

A graph of data from a mass spectrometer featuring peaks whose heights are measures of the numbers of ions of different masses produced from a sample in the spectrometer's ion source.

nanoparticle

An approximately spherical sample of matter with dimensions less than 100 nm (1 × 10 ^_7 m) .