Chemistry Basics Overview

Overview

This lecture reviews fundamental concepts in Grade 9 chemistry, focusing on matter classification, atomic structure, the periodic table, and ions.

Matter has mass and takes up space; it can be classified by composition as a mixture or a pure substance.
Pure substances contain only one type of particle and include elements (single type of atom) and compounds (two or more types of atoms in fixed proportions).
Mixtures contain two or more types of particles and can be homogeneous (one visible phase, particles uniformly distributed) or heterogeneous (multiple phases, particles not uniformly distributed).
Physical properties are characteristics observed with senses or instruments, such as state, color, or melting point.
Chemical properties describe a substance’s ability to react, for example, combustibility or reactivity with water.
Physical change alters physical properties only; no new substance forms (e.g., melting ice).
Chemical change produces at least one new substance with new properties.

Metals: good conductors, malleable, ductile, usually solid at room temperature, left side of periodic table.
Non-metals: poor conductors, brittle, varied state at room temperature, right side of periodic table.
Metalloids: have properties of both metals and non-metals, found along the staircase on the periodic table.

Atoms are composed of subatomic particles: protons (positive, in nucleus), neutrons (neutral, in nucleus), and electrons (negative, in shells).
Atomic number equals protons; mass number equals protons plus neutrons; in neutral atoms, protons = electrons.
Bohr-Rutherford model places electrons in shells: 1st (2 electrons), 2nd (8), 3rd (8), 4th (18).
Lewis dot diagrams show only valence electrons around the element symbol.

Organized by increasing atomic number, element types (metals, non-metals, metalloids), columns (groups/families), and rows (periods).
Group 1: Alkali metals; Group 2: Alkaline earth metals; Groups 3–12: Transition metals; Group 17: Halogens; Group 18: Noble gases.
Groups share similar chemical properties and valence electron counts.

Atoms gain or lose electrons to achieve a full valence shell, forming ions.
Anions are negatively charged (gain electrons); cations are positively charged (lose electrons).
The charge of an ion equals protons minus electrons.

Element — a pure substance made of one kind of atom.
Compound — a pure substance made of two or more elements chemically combined.
Homogeneous mixture — mixture with uniform composition throughout.
Heterogeneous mixture — mixture with non-uniform composition.
Physical property — characteristic observed without changing the substance.
Chemical property — characteristic describing a substance’s reactivity.
Ion — atom with unequal numbers of protons and electrons, giving it a charge.
Valence electron — electron in the outermost shell.
Group/Family — column of elements with similar properties in the periodic table.
Period — row in the periodic table.

Complete Bohr-Rutherford and Lewis dot diagrams for hydrogen, carbon, magnesium, and calcium.
Fill in missing elements on the periodic table and color-code metals, non-metals, and metalloids.
Practice determining the charge and symbols for given ions.
List and label group/family names and count valence electrons for selected groups.