HYS-DSE Chemistry Section 2: Atomic Structure, Periodic Table, Chemical Bonding, Structures and Properties

Vocabulary flashcards covering core definitions and concepts from HYS-DSE Chemistry Sections 2.1 through 2.4, including atomic structure, isotopes, periodic table trends, chemical bonding, and types of structures.

Matter

Anything which occupies space and has mass. It can be classified into pure substances and mixtures.

Element

A pure substance which cannot be broken down into anything simpler by chemical methods.

Compound

A pure substance made up of two or more elements chemically combined together in a fixed composition.

Mixture

Consists of two or more pure substances (elements or compounds) which have not chemically combined together and can be separated by physical methods.

Atom

The smallest part of an element which has the chemical properties of that element, consisting of protons, neutrons, and electrons.

Atomic number ($Z$)

The number of protons in the nucleus of an atom of an element.

Mass number ($A$)

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

Isotopes

Different atoms of the same element which have the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers).

Relative isotopic mass

The mass of a particular isotope of an element on the carbon-12 scale where ${}^{12}\text{C} = 12.00$.

Relative atomic mass (RAM)

The weighted average mass of an atom of an element relative to $\frac{1}{12}$ of the mass of a carbon-12 atom on the carbon-12 scale (${}^{12}\text{C} = 12.00$).

Electronic arrangement

The way in which electrons are arranged in the electron shells around the nucleus of an atom, filling from innermost to outermost shell up to a maximum of $2n^2$ electrons per shell $n$.

Octet rule

A chemical principle stating that an atom tends to attain stability by achieving eight electrons in its outermost electron shell (or two electrons for a single-shell duplet structure).

Period

A horizontal row in the Periodic Table; elements in the same period have the same number of occupied electron shells.

Group

A vertical column in the Periodic Table; elements in the same group (except helium) have the same number of electrons in their outermost shell.

Electronegativity

The ability of an atom of an element in a molecule to attract bonding electrons.

Alkali metals

Group I elements in the Periodic Table, which are soft, low-density metals that tarnish readily and react vigorously with water to form hydrogen gas and alkaline solutions.

Halogens

Group VII elements in the Periodic Table, which exist as toxic, colored diatomic molecules and decrease in reactivity down the group.

Noble gases

Group 0 elements that are colorless, odorless, chemically unreactive monoatomic gases with completely filled outermost electron shells.

Metallic bond

The strong non-directional electrostatic attraction between positive metal ions and delocalized electrons in a giant metallic structure.

Delocalized electrons

Electrons that leave the valence shells of metal atoms and are free to move throughout the three-dimensional metal lattice.

Cation

A positively charged ion formed when an atom (typically a metal) loses one or more outermost shell electrons.

Anion

A negatively charged ion formed when an atom (typically a non-metal) gains one or more electrons.

Isoelectronic

Chemical species (atoms or ions) that possess the exact same number of electrons and identical electronic arrangements.

Polyatomic ion

A charged group composed of two or more covalently bonded atoms carrying a net electrical charge, such as $\text{NH}_4^+$ or $\text{SO}_4^{2-}$.

Ionic bond

The strong non-directional electrostatic attraction between oppositely charged cations and anions.

Covalent bond

The strong directional electrostatic attraction between shared pairs of electrons and the positively charged nuclei of two bonded atoms.

Bond pair

A pair of shared electrons in a covalent molecule involved in holding two atoms together.

Lone pair

An unshared pair of outermost shell valence electrons in an atom within a molecule.

Dative covalent bond

A covalent bond in which both electrons of the shared bond pair are provided by a single donor atom possessing a lone pair.

Molecule

A neutral particle composed of two or more non-metal atoms chemically joined together by covalent bonds that can exist independently under room conditions.

Atomicity

The total number of atoms constituting a single molecule of an element or compound.

Relative molecular mass (RMM)

The sum of the relative atomic masses of all atoms present in a molecule of a covalent substance, carrying no unit.

Formula mass

The sum of the relative atomic masses of all atoms present in one formula unit of a substance.

Allotropes

Different structural forms of the same element in the same physical state, such as diamond, graphite, and buckminsterfullerene ($\text{C}_{60}$) for carbon.

Giant metallic structure

A regular three-dimensional arrangement of positive metal ions closely packed together in a "sea" of delocalized electrons.

Giant ionic structure

A three-dimensional crystal lattice composed of alternating positively charged cations and negatively charged anions held tightly by strong ionic bonds.

Giant covalent structure

A giant three-dimensional network structure where non-metal atoms are continuously linked together by strong covalent bonds.

Simple molecular structure

A structure composed of discrete molecules held together by weak intermolecular forces (van der Waals' forces), while atoms within each molecule are held by strong covalent bonds.