Grade 8 Science – Second Quarter Reviewer

These flashcards cover key concepts and terms for the Grade 8 Science Second Quarter topics, including atomic models, structures of atoms, isotopes, and the periodic table.

Atom

The basic unit of a chemical element, proposed to be made of tiny, indivisible particles.

Democritus

An ancient Greek philosopher who proposed that matter is made of indivisible particles called atomos.

John Dalton

Proposed the Solid Sphere Model, asserting atoms are solid spheres and combine in fixed ratios.

J.J. Thomson

Discovered the electron and proposed the Plum Pudding Model of the atom.

Rutherford's Gold Foil Experiment

Demonstrated that atoms are mostly empty space with a dense nucleus.

Nuclear Model

Model proposed by Rutherford indicating that most mass and positive charge are concentrated in a nucleus.

Niels Bohr

Proposed the Planetary Model, where electrons orbit the nucleus in fixed energy levels.

Modern Quantum Model

Describes electrons as moving in cloud-like regions around the nucleus, without a defined path.

Proton

A positively charged subatomic particle located in the nucleus, which identifies the element.

Neutron

A neutrally charged particle located in the nucleus that adds mass and stabilizes it.

Electron

A negatively charged particle that orbits the nucleus, responsible for chemical reactions.

Atomic Number (Z)

The number of protons in an atom, which also equals the number of electrons in a neutral atom.

Mass Number (A)

The total number of protons and neutrons in an atom.

Isotope

Atoms of the same element that have the same number of protons but different numbers of neutrons.

Compounds

Substances formed when two or more elements chemically combine in fixed ratios.

Mixture

A combination of two or more substances that are physically combined and can be separated by physical means.

Periodic Table

A chart organizing elements by increasing atomic number, grouping elements by similar properties.

Valence Electrons

Electrons in the outermost shell that determine an atom's chemical properties and reactivity.

Alkali Metals

Elements in Group 1 of the periodic table, known for being highly reactive.

Noble Gases

Elements in Group 18 that are stable and unreactive due to having a full outer shell of electrons.

Electron Configuration

The distribution of electrons among the energy levels of an atom, which helps locate an element on the periodic table.