Grade 9 Chemistry: Matter, Atoms, and the Periodic Table

Comprehensive vocabulary flashcards covering introductory chemistry concepts, including the particle theory of matter, classification of matter, physical and chemical properties and changes, atomic structure and history, isotopes, ions, electron configurations, and periodic table organization.

Matter

Anything that has mass and takes up space.

Particle Theory of Matter

A scientific model stating that all matter is made up of tiny particles that are always moving, have spaces between them, attract one another, and move faster when temperature increases.

Pure Substance

A form of matter made up of only one kind of particle with a constant composition, which cannot be separated by physical methods.

Mixture

Matter composed of two or more different substances mixed together with variable composition, containing more than one kind of particle.

Element

A pure substance that consists of only one type of atom and cannot be broken down into simpler parts by chemical methods (e.g., $\text{Fe}$, $\text{Cu}$, $\text{Au}$).

Compound

A pure substance formed when two or more different types of elements are chemically bonded together in fixed proportions (e.g., $\text{NaCl}$, $\text{H}_2\text{O}$, $\text{CO}_2$).

Molecule

A particle formed by two or more atoms chemically bonded together, containing atoms of one or more elements (e.g., $\text{O}_2$, $\text{H}_2\text{O}$).

Homogeneous Mixture

A mixture that looks uniform throughout, in which the different components are not individually visible and cannot be separated by physical filtration alone (e.g., dissolved salt water, brass, clean air).

Heterogeneous Mixture

A mixture in which the distinct components remain individually visible and can be separated by physical methods (e.g., oil-and-vinegar dressing, granite, sand mixed with water).

Physical Property

A characteristic of a substance that can be observed or measured without altering its chemical composition (e.g., color, density, melting point).

Qualitative Property

A physical property that is observed and described using words rather than numerical measurements (e.g., color, texture, odor, rough surface).

Quantitative Property

A physical property that is measured and expressed with a numerical value and unit (e.g., mass, volume, density, boiling point).

Lustre

The qualitative physical property describing a substance's ability to reflect light (e.g., shiny or dull).

Optical Clarity

The qualitative physical property describing the ability of light to pass through a substance, described as clear, transparent, translucent, cloudy, or opaque.

Viscosity

A physical property describing a fluid's resistance to flow (e.g., viscous, runny, or sticky).

Malleability

The physical property describing a solid's ability to be hammered or pressed into thin sheets without shattering.

Ductility

The physical property describing a solid's ability to be drawn or pulled out into thin wires.

Density

A quantitative physical property measuring the amount of mass contained within a specific unit of volume, calculated using $d = \frac{m}{V}$.

Physical Change

An alteration in the form, shape, or state of a substance that does not alter its underlying chemical composition (e.g., ice melting, water evaporating, slicing bread, dissolving sugar).

Chemical Property

A characteristic describing a substance's ability to react and change into one or more new substances with a new chemical composition (e.g., flammability, reactivity with oxygen, reactivity with acid).

Chemical Change

A process in which one or more substances are transformed into one or more entirely new substances with different compositions and properties (also known as a chemical reaction).

Evidence of a Chemical Change

The five primary indicators that a chemical reaction has taken place: color change, formation of a new odor, heat or light production, gas production (bubbles or fizzing), and formation of a precipitate.

Combustibility

A chemical property describing the ability of a substance to react with oxygen in the air and burn, releasing heat and light.

Atom

The basic building block of all matter and the smallest particle of an element that retains that element's chemical properties.

Nucleus

The tiny, dense, positively charged region at the center of an atom containing protons and neutrons, which provides almost all of the atom's mass.

Proton

A subatomic particle located in the nucleus with a positive charge ($+1$), a relative mass of $1\,\text{amu}$, whose count determines the element's identity.

Neutron

A subatomic particle located in the nucleus having no electrical charge ($0$) and a relative mass of $1\,\text{amu}$.

Electron

A negatively charged ($-1$) subatomic particle that orbits the nucleus within electron shells or the electron cloud, possessing negligible mass ($0\,\text{amu}$ or $\frac{1}{1836}\,\text{amu}$).

Atomic Number

The total number of protons found in the nucleus of an atom, uniquely defining which chemical element it is.

Mass Number (Atomic Mass)

The total sum of protons and neutrons located inside an atom's nucleus ($\text{protons} + \text{neutrons}$).

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons (e.g., carbon-12, carbon-13, and carbon-14).

Radiocarbon Dating

A scientific method that measures the decay of carbon-14 to determine the age of organic materials as old as approximately $60{,}000$ years.

Dalton's Theory

The 1803 atomic model proposing that atoms are the smallest, indivisible particles of matter and can be envisioned as solid spheres.

Thomson's Theory

The 1900 atomic model (plum pudding model) proposing that atoms consist of negatively charged electrons embedded randomly in a positive 'soup' or sphere.

Rutherford's Theory

The 1910 atomic model demonstrating that atoms are mostly empty space containing a small, dense, positively charged nucleus, with electrons orbiting like planets around the sun.

Bohr's Theory

The 1913 atomic model stating that electrons move around a positively charged nucleus in fixed orbits or specific energy levels (shells).

Electron Shell (Energy Level)

A region around the nucleus where electrons are likely to be found, holding a maximum of $2$ electrons in the 1st shell, $8$ in the 2nd, and $8$ in the 3rd.

Valence Electrons

The electrons located in the outermost electron shell of an atom that participate in chemical bonding.

Octet Rule

The principle stating that atoms form chemical bonds by gaining, losing, or sharing electrons to achieve a stable outer shell of $8$ valence electrons.

Ion

An atom that has acquired a positive or negative electric charge by losing or gaining one or more electrons.

Cation

A positively charged ion formed when a neutral atom loses one or more electrons (e.g., $\text{Na}^+$, $\text{Mg}^{2+}$, $\text{Ca}^{2+}$).

Anion

A negatively charged ion formed when a neutral atom gains one or more electrons (e.g., $\text{Cl}^-$, $\text{P}^{3-}$).

Lewis Dot Structure

A visual diagram of an atom or molecule that represents valence electrons as dots placed around the element's chemical symbol.

Periodic Table

A chart organizing the chemical elements into columns and rows according to repeating patterns of their physical and chemical properties.

Dmitri Mendeleev

The Russian chemist who developed the first periodic table by organizing elements based on repeating properties and predicting undiscovered elements.

Henry Moseley

The British scientist who refined the periodic table by arranging elements in order of increasing atomic number (number of protons).

Group (Family)

A vertical column on the periodic table containing elements that share similar chemical properties and the same number of valence electrons.

Period

A horizontal row on the periodic table indicating the number of electron shells an element possesses, along which atomic number increases and atomic size decreases from left to right.

Metals

Elements that are generally shiny, malleable, ductile, and good conductors of electricity and thermal energy (e.g., sodium, calcium, copper).

Nonmetals

Elements that are poor conductors of heat and electricity, lack ductility and malleability, and frequently exist as gases (e.g., oxygen, chlorine, nitrogen).

Metalloids

Elements that exhibit intermediate properties between metals and nonmetals and act as semiconductors (e.g., silicon, boron).

Alkali Metals

The highly reactive Group 1 elements (excluding hydrogen) with $1$ valence electron that are never found uncombined in nature.

Alkaline Earth Metals

The reactive Group 2 metals with $2$ valence electrons, which are hard, dense, have higher melting points than alkali metals, and exist only in compounds in nature.

Transition Metals

The metallic elements located in Groups 3 through 12 characterized by high melting points and good electrical and thermal conductivity.

Halogens

The very reactive Group 17 nonmetals with $7$ valence electrons whose name means 'salt forming' because they react with metals to form salts.

Noble Gases

The nonmetal elements in Group 18 with full valence electron shells ($8$ valence electrons, or $2$ for helium), rendering them extremely stable and unreactive.

Subscript

A small number written at the lower right behind an element symbol indicating the exact number of atoms of that element in a formula unit or molecule.

Coefficient

A number written in front of a chemical symbol or formula indicating how many individual atoms or molecules of that compound are present, multiplying all atoms within.