Grade 9 - Matter and Chemical Change

Section 1: Classifying Matter

Matter is anything that has mass and volume (occupies space).
The amount of matter in an object is called Mass. Mass can be measured in milligrams (mg), grams (g) or kilograms (kg). An object's mass remains the same.
Weight is a measure of the pull of gravity on an object. Therefore the weight of an object changes depending on the gravity. You would weigh less on the moon than you would weigh on Earth because the moon has less gravitational pull.

States of Matter

Matter can be found in three common states namely: solids, liquids and gases.

Solids: Solids have a shape and take up a definite amount of space. In solids, the particles of matter are packed tightly and mostly in a regular pattern. The pencil, pen, book, desk, blocks, wood, ice ... are all solids.

Liquids: Liquids do not have a definite shape, they take the shape of the container. Juice is a liquid, if you pour it into a glass, it will spread out and take up the shape of the glass. In liquids, the particles that make up matter are farther apart and can move more freely than in solids. Water, juice, milk, and oil are examples of liquids.

Gases: If you pour juice into a glass, it goes to the bottom of the glass makes the glass half full. Gases do not have a definite shape. In addition, if you put a gas into a container, it spreads out throughout the container. In gases, the particles spread out so as to fill the space in the container. If the space is small, the particles will be tight together, if the space is big, the particles will be spread out farther apart. Air is mostly made out of gases.

The most common form of matter in our universe exists in a fluid state called plasma, which is a gaslike mixture of positively and negatively charged particles. It is often considered to be the fourth state of matter.

All substances are either pure or mixtures. Pure substances can either be elements or compounds. Pure substances have unique set of properties, or characteristics that remain consistent. Mixtures can either be homogenous or heterogenous based on the interactions between the elements in the mixture.

Element

An element is a pure substance with its own set of physical and chemical properties that cannot be broken down into simpler chemical substances. It has only one type of atom present.

Compound

A compund is a pure substance that can be broken down by a chemical change into two or more elements. Compounds have more than one type of elements that are chemically combined.

Mixtures are two or more substances that are NOT chemically combined. They do not have constant characteristics such as boiling or melting points. The components retain their characteristic properties. They may be separated into pure substances by physical methods. Mixtures of different compositions may have widely different properties.

Homogenous Mixtures

These are mixtures which look as though they have only one set of properties. The blended mixture has equal amounts of both substances (all parts of the mixture are the same). If the homogenous mixture does not have any settling of any of the substances it is made of, then it is called a solution. Solutions occur because each particle interacts with other particles and the resultant particles are evenly distributed throughout the entire mixture.

In solutions, the substance in the smallest amount and the one that dissolves or disperses is called the SOLUTE. The substance in the larger amount is called the SOLVENT. water is commonly called the universal solvent. The gases, liquids, or solids dissolved in water are the solutes.

Heterogenous Mixtures

In a heterogenous mixture, the properties of the pure substances, can still be observed. If you notice there are two or more materials that are visible within a mixture, then it is a heterogeneous mixture.

Other Types of Mixtures

A suspension is a mixture made of parts that separate upon standing. To make a suspension, add fine sand to a bottle of water. Shake it, and watch the particles move. Soon, the sand particles will separate from the water and settle to the bottom of the bottle. You can separate a suspensio by filtration.

An emulsion is a suspension of two liquids that usually do not mix together. Emulsions are stable homogeneous mixtures of very small droplets suspended, rather than dissolved, in a liquid.

A colloid is a stable homogeneous mixture in which very small, fine particles of one material are scattered throughout another material, blocking the passage of light without settling out. Fog is a liquid-in-gas colloid. Smoke is a solid-in-gas colloid. Nonfat milk is a solid-in-liquid colloid.

Section 2: Changes In Matter

Matter can change from one form to another, or create new materials Every kind of matter has its own distinguishing characteristic properties that can be used to identify the kind of matter it is. Properties are characteristics that can be used to describe how a substance behaves substance. These properties can be physical or chemical. Changes that matter can undergo fall into two classification categories: physical change and chemical change. A physical change occurs when a material changes form but not composition. A change of state is an example of a physical change where energy is used or released.

Changes of State: A change of state occurs when the particles of a substance gain or lose energy. Because this change is due to kinetic energy, the change of state is a physical process, which is reversible, and no matter how much kinetic energy is put into or taken away from the material, the material will always stay the same and its mass will also remain the same.

A chemical change occurs when two or more substances react and create one or more new substances. It is often permanent, although not always. Combustion is an example.

Properties of Chemical or Physical Change

Any property that can be observed without forming a new substance is a physical property. These can include: color, texture, luster, smell, state, melting point, boiling point, hardness, malleability, ductility, crystal shape, viscosity, solubility, density and conductivity (electrical and heat). Any property that describes how a substance reacts with another substance when forming a new substance is a chemical property. Chemical properties include: reaction with acids, ability to burn (combustibility), reaction with water, behaviour in air and reaction to heat, toxicity, stability.

How do you know a chemical change has occured?

There are some tell tale signs that you can use to detect if a chemical reaction has occured. For instance:

Change in color
Release of gas
Smell
Change in temperature - the substance could either become warmer or colder.
Sometimes chemical reactions result in production of energy such as light. Fire is good example here.

Another term for a chemical change is chemical reaction. Chemical reactions have two parts. A substance present before a chemical change is a reactant. A substance produced by a chemical change is a product. A chemical equation uses letters and numbers to represent the amounts of reactants and products involved in a chemical change. An arrow separates the reactants on the left from the products on the right.

Section 3: Elements

An element is a pure substance made up of only one type of particle, or atom. Each element has its own unique set of distinguishing properties and cannot be broken down into simpler substances by means of a chemical change.

A compound is a pure substance made up of 2 or more elements chemically combined together. Compounds can be broken down into the elements that they are composed of.

An atom is a particle that consists of a nucleus, which contains protons and neutrons, surrounded by a cloud of electrons. The atom is the basic particle of the chemical elements. Different elements can be distinguished from each other by the number of protons that are in their atoms.

Atoms are extremely small. A human hair is about a million carbon atoms wide.

More than 99.9% of an atom's mass is in the nucleus. Each proton has a positive electric charge, while each electron has a negative charge, and the neutrons, if present, have no electric charge. If the numbers of protons and electrons are equal, as they normally are, then the atom is electrically neutral. If an atom has more electrons than protons, then it has an overall negative charge, and is called a negative ion (or anion). On the contrary, if an atom has more protons than electrons, it has a positive charge, and is called a positive ion (or cation).

Atomic Models

1. Dalton's Model

This model is also described as the billiard balls model. In 1803, John Dalton conducted experiments with gases and used the results to propose the modern theory of the atom based on the following assumptions.

Matter is made up of atoms that are indivisible and indestructible.
All atoms of an element are identical.
Atoms of different elements have different weights and different chemical properties.
Atoms of different elements combine in simple whole numbers to form compounds.
Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.

2. Thomson's model

This model is also described as the plum pudding model. The positive charges fills the atom while the electrons were embedded throughout the atom. Thomson discovered the electron and since the electron was negative, but atoms neutral, there had to be positive charge inside atoms. Thomson used a beam of cathode rays in a CRT with both an electric field and a magnetic field perpendicular acting on the beam. With only the electric field on, the beam was deflected toward the positive plate. With only the magnetic field on, the cathode rays were deflected into a curved path. When both fields were on, and the field strengths equal, the cathode rays were not deflected.

3. Rutherford's Model

Around 1911 Rutherford, Marsden and Geiger performed experiments to test the Thomson model. They directed alpha particles from radioactive sources onto thin gold foils. The Thomson model predicted that most of the alpha particles would go straight through, and only a few would be deflected at small angles since the electrons in the atom have much less mass than alpha particles. Most of the particles went straight through undeflected, some were deflected at angles of more than 10^o and a few were deflected almost straight back. He concluded that most of the atom was empty space with most of the mass and all of the positive charge concentrated in a very small region (the nucleus). Scattering angles indicated the size of the nucleus was about 10¹⁵ to 10¹⁴m in radius.

In Rutherford's model, electrons could 'orbit' the nucleus at any energy level. The closer the alpha particle is to the nucleus the greater its potential energy.

Evolution of the Atomic Theory

Stone age (8000 BC) - Matter was made up of solid material, which could be fashioned into tools.
Bronze age (4500 BC) - The effect of heat on copper, lead to the creation of a strong material (bronze) for use as tools.
Iron age (1200 B.C) - Iron combined with carbon to make steel, for even stronger tools.
350 B.C. - Atomos particles : Developed the theory that everything was made out of Air – Water - Earth – Fire
1500 - Theory of matter based on experimentation. (History of Alchemy).
1660 - Observations that particles can be compressed.
1770 - System for naming chemicals was developed. The first periodic table was developed.

Brief History of Atomic Models:

1808: Dalton's Atomic Theory: Billiard ball model.
1897: JJ Thomson Atomic Model : Raisin bun model (Plum pudding model).
1904-1911: Rutherford Model: Planetary model. Negatively charged particles orbit around a nucleus.
1913-1922: Niels Bohr Model - Atomic Model: Electrons rotate randomly around the nucleus.
2000s: Quantum Model: The atom consists of a cloud of electrons around a nucleus.

Section 4: Kinds of Elements

An element is identified by the number of protons contained in the nucleus of each of its atoms. Every element has a unique number of protons and is defined as the element's atomic number.

Mass Number - The atomic mass number of an element is simply the sum of the protons and neutrons in the nucleus of 1 atom of the element.

Atoms of the same element may have different numbers of neutrons, which means they will have different mass number. Atoms of the same element that have different atomic masses are called isotopes. If you look at a detailed periodic table, you will notice that an isotope’s atomic mass is listed beside its name or symbol.

The atomic mass is the average mass of an element in atomic mass units (amu.) The mass in an atom is roughly the mass of one proton or neutron. The atomic mass is a decimal number on the Periodic Table because it's an average of the various isotopes (one or more atoms that have the same atomic number but different mass numbers) of an element.

One way of classifying elements is to sort them into categories, based on their distinct properties. Long before anyone knew any detail about the atoms or any of the periodic properties the elements were divided into two broad categories → metals and non-metals.

Scientists classify metals into 3 categories: Alkali metals, Alkaline metals and transition metals.

Alkali metals are Group 1 elements located on the far left of the periodic table along with Hydrogen which is not a metal. Alkali metalks include Sodium (Na), Lithium (Li) and Potassium (K). They are soft and extremely reactive, therefore they easily form compounds with other substances. They never exist by themselves in nature.

Alkaline metals are located to the right of alkali metals. These are not as reactive as the alkali metals, but they are also soft and light. They include Calcium (Ca), Magnesium (Mg) etc. They are essential to many living things.

Transition metals are a large group of elements in the center of the periodic table. They include copper, iron, gold, nickel, and zinc. Most transition metals are hard and shiny. They react slowly with other substances. Transition metals are used to make coins, jewelry, machinery, and many other items.

On the right side of the periodic table are metalloids and nonmetals.

Metalloids include silicon, boron, and arsenic. They share properties with both metals and nonmetals. They are semiconductors, i.e., at high temperatures they conduct electricity, like metals, but at very low temperatures they stop electricity from flowing, like nonmetals. Because of this, silicon and other metalloids are used in machinery, computer chips, and circuits. Nonmetals, such as oxygen, carbon, and nitrogen, have properties opposite to those of metals. At room temperature, most of them exist as gases or as brittle solids. Nonmetals cannot be rolled into wires or pounded into thin sheets. Most nonmetals are poor conductors of heat and electricity.

Noble gases, in the far-right column in Group 18 of the periodic table, are nonmetals that do not react naturally with other elements. These gases have many uses. Argon is used in electric light bulbs. Neon, when exposed to electricity, produces the bright colors of some signs. Xenon is used in car headlights. Helium is often used in balloons.

To the left of the noble gases are elements called halogens. These include fluorine and chlorine. They are very reactive nonmetals. Chlorine combines with sodium to form sodium chloride (table salt).

Rare Earth Elements - There are 30 rare earth elements. Many of them are synthetic or manmade. They're found in group three of the periodic table and the sixth and seventh groups.

Section 5: Chemical Compounds

A compound is a formed when two or more elements combine together in a chemical reaction. Compounds can be classified as acids, bases or neutral compounds. Acids turn blue litmus paper red, bases turn red litmus paper blue, and neutral compounds cause no effect on litmus papers. Compounds can also be classified depending on the type of bond joining the component elements, such as ionic bond (Ionic compounds) or covalent bond (Molecular compounds). Ionic compounds are created by the reaction between a metal and a non-metal. Ionic compounds are solids in nature and soluble in water. They conduct electricity in aqueous solution. Ionic hydrates are ionic compounds that contain loosely bonded water molecules. Hydrated compounds appear different from unhydrated compounds. For example, hydrated copper II sulfate forms blue crystals, while the unhydrated form is a white powder. Molecular compounds are created by the reaction between a non-metal and a non-metal. Molecular compounds are either solid, liquid or gases, depending on the component elements. Their solubility also varies, and they do not conduct electricity in aqueous solutions. A molecule is a group of nonmetal atoms held together by covalent bonds. The molecular formula indicates the number of atoms of each type.

Understanding Formulas for Compounds

Compounds have a chemical name and a chemical formula. The chemical formula uses symbols and numerals to identify which elements and how many atoms of each element are present in the compound. For example:
Ethanol ( C₂ H₆ O ) has 2 carbon atoms, 6 hydrogen atoms and 1 oxygen atom. To determine a chemical name, a standardized chemical naming system, or nomenclature, is used. The IUPAC ( International Union of Pure and Applied Chemistry ) is responsible for determining the appropriate name for each compound.

How Are Molecular Compounds Named?

A compound made from two elements is called a binary compound. Rules for naming binary molecular compounds:

The first element in the compound uses the element name
The second element has a suffix – ide
When there is more than 1 atom in the formula, a prefix is used which tells how many atoms there are
Exception to #3 above – when the first element has only 1 atom the prefix mono is not used

Examples: CO₂(g) carbon dioxide, CCl₄(l) carbon tetrachloride, SiO₂(s) Silicon dioxide.

How Are Ionic Compounds Named?

Two rules:

The chemical name of the metal or positive ion goes first, followed by the name of the non-metal or negative ion.
The name of the non-metal negative ion changes its ending to ide.

One exception – Where negative ions are polyatomic ions, the name remains unchanged.

All ionic compounds have distinct (different) crystal shapes.

Section 6: Chemical Changes and Reaction Types

A chemical reaction is said to have occurred when one of the following observations are made. These observations can be classified into physical, chemical or nuclear changes.

Physical changes
State or energy change: This involves the change from solid to liquid or to gaseous state. The energy change is usually small. There is no new substance formed.

Chemical changes
This may include color change, change in odor, physical state and energy change. A new substance is formed, and the changes may be irreversible. Chemical changes are associated with moderate energy changes, higher than physical changes.

Nuclear changes
Nuclear changes often result in emission of radiation energy. New elements are formed, and the energy change is usually much larger than chemical changes.

The evidence of a chemical reaction can be explained using the major aspects that change when a chemical reaction occurs. These include:

Color change: A color change could indicate that the product is different from the reactants. For example if a solution changes from colorless to blue.
Odor change: The final products may have a different smell from the reactants.
State change: If the products are of a different state compared to the reactants. Mostly, for example, if a substance changes into a gas or if a solid precipitate is formed.
Energy change: When a chemical reaction occurs, energy, in form of heat, light, sound, or electricity is either absorbed by the reaction or emitted from the reaction. Combustion of fuels is obviously a good example. If energy is absorbed by the reaction, the reaction is called endothermic , if energy is released by the reaction, the reaction is called exothermic.

Types of Reactions

cReactions can be classified into five different types as follows:

Formation Reactions: Two or more elements reach to form a product. A + B → AB.
Simple decomposition: A reaction where a compound is broken down into its constituent elements. AB → A + B.
Single replacement reaction: A reaction between an element and a compound, where the compound is broken down into constituent elements, and forms a compound with the reactant-element. A + BC → B + AC. Within the reactants, the element could be either a metal or a nonmetal.
Double replacement reaction: Occurs when two compounds react and swap their bonding elements. AB + CD → AD + CB.
Combustion reactions: Burning of a substance with sufficient oxygen available to produce the most common oxides of the elements making up the substance that is burned. Many combustion reactions use hydrocarbons and release carbon dioxide and water as products.

Chemical reactions can be written as word equations which gives the names of all the reactants (separated by a "plus' sign + ) followed by an arrow which points to the names of all the products.

Iron + Oxygen + Water → Rust

Iron plus oxygen plus water produces rust

Iron, oxygen and water are the reactants. Rust is the product.

Breaking Chemical Bonds

Chemical bonds are forces that cause a group of atoms to behave as a unit. Energy is stored in these bonds. To break the bonds energy must be added. When bonds form, energy is released. All chemical reactions involve energy being absorbed ENDOTHERMIC, or released EXOTHERMIC. Photosynthesis is an endothermic reaction, because it needs light energy to occur, whereas combustion is an exothermic reaction, because it gives off light and heat.

Section 7: Reaction Rate

The speed of a chemical reaction is called the reaction rate.

Temperature of the reactants affects the rate of all reactions (The higher the temperature the faster the reaction rate)
Surface Area of the reactants affects the reaction rate (The more surface in contact, the faster the reaction rate)
Concentration of the reactants affects the reaction rate. (The higher the concentration, the faster the reaction rate)
The presence of a Catalyst affects the reaction rate

Catalysts speed up reactions

A catalyst is a substance that help a reaction proceed faster and are not consumed in the reaction.

Several types of reactions involving catalysts can be found in living and non-living things. Enzymes are natural catalysts that help in the reactions in the body, which break down food. They also get rid of poison in the body. Catalase (an enzyme found in plant and animal cells) speeds up the breaking down of hydrogen peroxide into harmless oxygen and water.

Inhibitors slow down chemical reactions

Inhibitors are substances that slow down chemical reactions. Plants have natural inhibitors in their seeds to prevent germination until the right conditions are present. Inhibitors are added to foods to slow down their decomposition.

Combustion

Combustion is the highly exothermic combination of a substance with oxygen. Combustion requires heat, oxygen, and fuel. The products of combustion include carbon dioxide and moisture.

Burning fossil fuels (such as propane) produces carbon monoxide, carbon dioxide, sulfur oxides, nitrogen oxides, smoke, soot, ash and heat. Some of these products are pollutants.

Corrosion

Corrosion is a slow chemical change that occurs when oxygen in the air reacts with a metal. Corrosion is a chemical reaction in which the metal is decomposed (eaten away), when it reacts with other substances in the environment. The corrosion of iron is called 'rusting'.

Preventing Corrosion

Involves protecting metal from contact with the environment and the factors that affect the reaction rate of this chemical reaction.

Coating a corrosive metal with a thin layer of zinc is called galvanization.
The process of coating a corrosive metal with another metal through electrolysis is called electroplating.
Painting the material.

I once told you a Chemistry joke, but you showed no reaction.