Chapter 2 Atoms and Molecules Flashcards
Element
A chemical element (or element) is a chemical substance consisting of atoms having the same number of protons in their atomic nuclei (i.e. the same atomic number, Z).[1] There are 118 elements that have been identified, of which the first 98 occur naturally on Earth with the remaining 20 being Synthetic elements.
Chemical symbol
In chemistry, a symbol is a code for a chemical element. It is usually derived from the name of the element, often in Latin.
Atom
An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is made up of neutral or ionized atoms.
Matter
The substance or substances of which any physical object consists or is composed:
Electron
The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure.
Proton
The proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with mass approximately one atomic mass unit, are collectively referred to as “nucleons”.
Neutron
The neutron is a subatomic particle, symbol n or n0, with no net electric charge and a mass slightly larger than that of a proton. Protons and neutrons, each with mass approximately one atomic mass unit, constitute the nucleus of an atom, and they are collectively referred to as nucleons.
Atomic nucleus
Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus with a very small contribution from the orbiting electrons. Neutrons have no charge and protons are positively charged. Because the nucleus is only made up of protons and neutrons it is positively charged
Atomic number
Atomic number is the number of protons, and therefore also the total positive charge, in the atomic nucleus.
Periodic Table
A table of the chemical elements arranged in order of atomic number, usually in rows, so that elements with similar atomic structure (and hence similar chemical properties) appear in vertical columns.
Electron configuration
In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals.
Atomic mass unit
The unified atomic mass unit (symbol: u) or dalton (symbol: Da) is the standard unit that is used for indicating mass on an atomic or molecular scale (atomic mass). One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is equivalent to 1 g/mol.
Atomic mass
For atoms, the protons and neutrons of the nucleus account for almost all of the mass, and the atomic mass measured in u has nearly the same value as the mass number.
Isotopes
A mixture of atoms with different number of neutrons and thus different masses.
Radioisotopes
Radioisotopes are radioactive isotopes of an element. Different isotopes of the same element have the same number of protons in their atomic nuclei but differing numbers of neutrons. They can also be defined as atoms that contain an unstable combination of neutrons and protons.
Autoradiography
An autoradiograph is an image on an x-ray film or nuclear emulsion produced by the pattern of decay emissions (e.g., beta particles or gamma rays) from a distribution of a radioactive substance.
Orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.
Principal energy level
The principal quantum number tells us the main energy level or shell of an electron, and gives us an idea of the electron density around the nucleus. It also tells us the number of nodes, how many subshells there are and the maximum number of electrons for each shell.
Electron shell
An electron shell is the outside part of an atom around the atomic nucleus. It is a group of atomic orbitals with the same value of the principal quantum number n. Electron shells have one or more electron subshells, or sublevels.
Valence shell
The valence shell is the outermost shell of an atom. It is usually (and misleadingly) said that the electrons in this shell make up its valence electrons, that is, the electrons that determine how the atom behaves in chemical reactions.
Valence electrons
The valence electrons (VE) are the electrons in the outer shell of an atom. The valence electrons are the ones involved in forming bonds to adjacent atoms. Therefore, the number of VE is important for determining the number of bonds an atom will form, the number of unpaired electrons, and an atom’s formal charge.
Compound
A compound is a molecule made of atoms from different elements. All compounds are molecules, but not all molecules are compounds. Hydrogen gas (H2) is a molecule, but not a compound because it is made of only one element.
Molecule
A molecule is the smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecules are made up of atom s that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electron s among atoms.
Chemical formula
A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using a single line of chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs.
