Chemistry Chapter: Matter and Its Properties

Matter that has a uniform and definite composition. It's made up of either elements or compounds.

The purest form of matter. It cannot be broken down into simpler substances.

A substance formed when two or more elements chemically combine in a fixed ratio. Examples: water (H2O), salt (NaCl).

A blend of two or more substances where each substance keeps its own properties. They can be either homogenous or heterogeneous.

A mixture where the components are evenly distributed throughout. It appears uniform. An example is salt dissolved in water.

A mixture where the components are not evenly distributed. You can see the separate components. An example is sand in water.

A chemical property describes how a substance reacts or changes during a chemical reaction. Example: Flammability (a substance's ability to burn).

A chemical change always involves the formation of new substances with different properties. Example: rusting of iron.

A physical change occurs when the appearance or form of a substance changes but the substance's chemical composition remains the same. Examples include melting ice, boiling water, or chopping wood.

The law of conservation of mass states that in any physical change or chemical reaction, the total mass of the reactants before the change is equal to the total mass of the products after the change.

Absolute zero is the lowest temperature possible, estimated at -273.15° Celsius or -459.67° Fahrenheit. At this point, all molecular motion ceases, and there is no heat.

Ionic solids consist of positively and negatively charged ions held together by electrostatic forces. These solids are often hard, brittle, and have high melting points.

Dalton's Atomic Theory states that all matter is made up of tiny indivisible particles called atoms. Atoms of the same element are identical, while atoms of different elements have different masses. Compounds are formed by the combination of atoms of different elements.

Thomson's cathode ray tube experiment led to the discovery of electrons. The experiment involved a beam of negatively charged particles traveling from the cathode to the anode. This discovery led to Thomson's Plum Pudding Model of the atom.

Rutherford's gold foil experiment showed that atoms are mostly empty space with a small, dense, positively charged nucleus at the center. Alpha particles were fired at a gold foil, and some passed straight through, while others were deflected or bounced back.

The tiny central core of an atom, composed of protons and neutrons.

Positively charged subatomic particles found in the nucleus.

Neutral subatomic particles found in the nucleus. They have nearly the same mass as protons.

Fixed energy levels that electrons occupy in an atom, like steps on a ladder.

The amount of energy needed to move an electron from one energy level to another.

A region around the nucleus where there is a high probability of finding an electron.

The number of protons in the nucleus of an atom.

The number of protons in an atom never changes during a chemical reaction.

The amount of energy needed to remove one electron from a neutral atom in its gaseous state.

A measure of an atom's ability to attract electrons towards itself when forming a chemical bond.

The electrostatic forces that hold oppositely charged ions together in a compound.

A chemical reaction is balanced when the number of atoms of each element on the reactants' side equals the number of atoms of that element on the products' side.

Electrons occupy specific energy levels around the nucleus, each corresponding to a different distance from the nucleus.

An orbital is a region of space within an energy level where an electron is most likely to be found.

The maximum number of electrons that can occupy a specific energy level is determined by the formula 2n² where 'n' is the energy level number (1, 2, 3 etc.).

Electrons in the highest energy level of an atom are called valence electrons.

The Octet Rule states that atoms tend to gain, lose, or share electrons to achieve a stable configuration with 8 valence electrons.

An ion is an atom or group of atoms with a net electric charge, either positive (cation) or negative (anion).

An atom's loss of valence electrons results in a positively charged ion called a cation.

An atom's gain of negatively charged electrons results in a negatively charged ion called an anion.

The distance between the nuclei of two atoms in a molecule.

Elements that share properties of both metals and nonmetals.

Group 1 of the periodic table. They are highly reactive metals that readily lose one electron.

Group 17 of the periodic table. Highly reactive nonmetals that tend to gain one electron.

A line spectrum produced when an atom absorbs energy and then emits light as its electrons transition back to lower energy levels.

Elements in Group 18 of the periodic table. They are very unreactive due to their full outer shell of electrons.

Metals readily lose their valence electrons, making them good conductors of heat and electricity. They are malleable, ductile, and shiny.