Grade 9 Chemistry

Properties of Matter

Atomic Structure

The Periodic Table

Chemical Bonds

Chemical Reactions

An element has a fixed composition because it contains only one type of atom. 

A compound always contains two more more elements joined in a fixed proportion. 

The properties of a mixture can vary because the composition of a mixture is not fixed. 

Viscosity, conductivity, malleability, hardness, melting point, boiling point, and density are examples of physical properties that can be used to identify a material, to choose a material for a specific purpose, or to separate the substances in a a mixture.  

Chemical properties can be observed only when the substances in a sample matter are changing into different substances. Three common types of evdience for a chemical change are a change in color, production of a gas, and formation of a precipitate. 

When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of matter remains the same. 

Protons, electrons, and neutrons are subatomic particles that can be distinguished by mass charge, and location in an atom.

Atoms of different elements have different number of protons. 

Isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons. 

Scientists use the electron cloud model to describe the possible locations of electrons around the nucleus, which is a good approximation of how electrons behave in their orbitals. 

Modern periodic table is organized by increasing atomic number. Each row is a period. Each column is a group. Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups. 

Atomic mass is avlue that depends on the distrubtion of an element's isotopies in nature and the masses of those isotopes. 

Elements are classified as metals, nonmetals, and metalloids. Across a period from left to right, the elements become less metallic and more nonmetallic in their properties. 

Elements in a group have similar properties because they have the same number of valence electrons. 

When the highest occupied energy level of an atom is filled with electrons, the atom is stable and not likely to react.

Some elements achieve stable electron configurations through the transfer of electrons between atoms. An ionic bond forms when electrons are transferred from one atom to another. 

The attractions between the shared electrons and the protos in each nucleus hold the atoms together in a covalent bond. 

The law of conservation of mass states that mass is neither created nor destroyed. 

In order to show that mass is conserved during a reaction, a chemical equation must be balanced, which means the total number of atoms for each element/compound on each side of an equation are equal to one another. 

Chemists use a unit called the mole to measure amounts of a substance because chemical reactions involve large numbers of small particles.

In chemical reactions, the mass of a reactant or product can be calculated using a blanaced chemical equation and molar masses. 

The general types of chemical reactions are synthesis reactions, decomposition reactions, single-replacement reactions, double-replacement reactions, and combustion reactions. 

Chemical reactions involve the breaking of chemical bonds in the reactants and formation of chemical bonds in the products. 

During a chemical reaction, energy is either released or absorbed. 

Reaction rates tell you how fast a reaction is going. 

Factors that affect reaction rates include temperature, surface area, concentration, stirring, and catalysts. 

When a physical changes does not go to completion, a physical equilibrium is established between the forward and reverse changes. When a chemical reaction does not go to completion, a chemical equilibirium is establisehed between the forward and reverse reactions.