Grade 9 Chemistry: Properties and Changes

• Grade 9 chemistry review notes

Properties

• Physical properties are features observed without changing the substance's composition, such as color, mass, ductility, malleability, viscosity, odor, state, density, texture, solubility, luster, and hardness
• Chemical properties describe a substance's ability to undergo changes in composition and produce new substances, including reactivity with water, acids, or oxygen, flammability, pH, heat of combustion, and toxicity

Physical vs Chemical Changes

• Physical changes do not produce a new substance and examples include cutting, dissolving, and changes of state
• Chemical changes produce a new substance
• Signs of chemical changes include heat or light production, difficulty to reverse, color change, precipitate formation, and gas production (air bubbles)

Gas Tests

• Hydrogen gas produces a popping noise when tested with a burning splint
• Oxygen gas causes a glowing splint to reignite
• Water vapor turns cobalt (II) chloride paper blue to pink
• Carbon dioxide turns limewater cloudy

Periodic Table

• Group 1 elements are the alkali metals
• Group 2 elements are the alkaline earth metals
• Groups 3-12 elements are the transition metals
• Group 13 elements are the metalloids
• Groups 14-17 elements are the halogens
• Group 18 elements are the noble gases

Metals vs Non-Metals

• Metals are located on the left side of the periodic table, are shiny, malleable, good conductors, and react with acids; most are solid at room temperature, except mercury (Hg)
• Non-metals are located on the right side of the periodic table, are dull, brittle, poor conductors, and do not react with acids

Atomic Structure

• Protons are located in the nucleus, have a positive (+) charge, and the symbol p
• Neutrons are located in the nucleus, have no charge (neutral), and the symbol n
• Electrons orbit the nucleus, have a negative (-) charge, and the symbol e

Atomic Notation

• Includes the element symbol, atomic mass (top left), and atomic number (bottom left)
• Protons = electrons = atomic number
• Neutrons = atomic mass - atomic number
• Subscripts indicate the number of atoms of each element in a molecule (e.g., O2 means two oxygen atoms)

Diagrams

• Bohr-Rutherford diagrams show electrons in orbits with a maximum number in each orbit (2, 8, 8, 18)
• The atomic number indicates the number of electrons to draw
• Lewis diagrams show electron transfer between a metal and non-metal in ionic compounds, or electron sharing between two non-metals in covalent compounds
• One dash in Lewis diagrams represents one pair of shared electrons
• Two dashes represent two pairs of electrons
• Three dashes represent three pairs of electrons

Naming Compounds

• Metal atoms lose electrons to form positive ions, while non-metal atoms gain electrons to form negative ions

Binary Ionic Compounds

• They consist of a metal and a non-metal
• The first part of the name is the positive metal ion name
• The second part is the negative non-metal ion name with the ending changed from "ine" to "ide"
• In CaCl₂, Ca is the positive ion (cation), Cl is the negative ion (anion), and 2 is the subscript indicating the number of ions

Zero-Sum Rule

• The sum of all charges in a chemical formula must equal zero: total positive charges = total negative charges

Multivalent Metal Ions

• Meaning they can form more than one possible ion
• The first part is the name of the positive ion
• The second part includes a Roman numeral in brackets to indicate the ion's charge (I, II, III, IV...)
• The third part is the negative non-metal ion name with the ending "ide"
• For Iron (II) Sulphide, iron's charge is 2+ (indicated by Roman numerals), and sulphide's charge is 2-

Polyatomic Ionic Compounds

• They consist of a metal and polyatomic ion
• The first part of the name is the positive metal or polyatomic ion name
• The second part is the negative polyatomic ion name

Molecular Compounds

• Form when two non-metals combine and share electrons
• The first part of the name is the non-metal that comes first in the formula
• The second part is the non-metal written last in the formula with the ending changed to "ide"
• Use a prefix to indicate the number of atoms: 1=mono, 2=di, 3=tri, 4=tetra, 5=penta, 6=hexa, 7=hepta, 8=octa, 9=nona, 10=deca

Chemical Reactions

• Chemists use equations to describe chemical reactions, in which an arrow means "yields", "forms", “produces" and + separates two or more reactants or products
• The two main types of equations are word equations and chemical equations

Word Equations

• Uses chemical names to describe reactants and products in a chemical reaction
• Example: Iron + sulfur -> iron (II) sulfide + energy

Chemical Equations

• Uses chemical formulas to describe the reactants and products in a chemical reaction and includes the state of each substance: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solutions

Types of Chemical Equations

• Skeleton chemical equations translate chemical names into chemical formulas
• Balanced chemical equations show an equal number of each kind of atom on both sides of the equation
• Balance skeleton chemical equations to ensure the law of conservation of mass
• Do not alter any chemical formulas or subscripts when balancing equations
• You can only change the number of atoms by changing the coefficient in front of the formula
• Balance polyatomic ions as a group if possible and balance single elements last

Standard States of Elements

• Most elements in the periodic table are monatomic in their standard state, with exceptions: H2 (g), F2 (g), S8 (s), N2 (g), Cl2 (g), P4 (s), O2 (g), Br2 (l), and I2 (g)

Law of Conservation of Mass

• In any chemical reaction, the total mass of the reactants equals the total mass of the products, so a chemical reaction must show an equal number of each kind of atom on both sides of the equation

Types of Chemical Reactions

• Synthesis, where two reactants combine to form a larger or more complex products (A + B → AB)
• Decomposition, where a large compound breaks down into two or more smaller compounds (AB → A + B)
• Single Displacement, where one element replaces another in a compound (A + BC → AC + B)
• Double Displacement, where two ionic compounds exchange ionic partners (AB + CD → CB + AD)
• Combustion, where a substance burns or reacts quickly with oxygen, forms oxides, and releases energy (X + O2 (g) → XO + energy), and requires lots of O2 and burns quickly
• Exothermic reactions release energy as a product where vessels get warm or hot
• Endothermic reactions absorb energy as a reactant where vessels get cold

Acids & Bases

• Acids are molecular compounds sharing similar chemical and physical properties
• Acid physical properties: sour taste and conduct electricity
• Acid chemical properties: react with metals, turn litmus paper red and neutralize bases

Acids

• All acids release Hydrogen ions when they dissolve in water
• Binary acids contain Hydrogen and a non-metal, name begins with the prefix 'Hydro-' and ends with acid
• Oxyacids contain a polyatomic ion (that contains oxygen) and a hydrogen ion, named after the polyatomic ion with the ending changed to "-ic" followed by the word acid

Base

• Bases share similar chemical and physical properties
• Basic physical properties: taste bitter, feel slippery and conduct electricity
• Basic chemical properties include turning litmus paper blue and reacting with natural products
• Most bases are ionic compounds with a hydroxide, some contain carbonate ions and can neutralize acids

pH

• Used to measure acidity or basicity
• Meaning "POWER of HYDROGEN
• pH range: pH of 1-6 is ACIDIC, pH of 7 is NEUTRAL and pH of 8-14 is BASIC
• The pH scale is based on a LOGARITHMIC scale. 1 unit on the pH scale shows a 10 x effect on the concentration in solution
• pH affects soil for plants; different plants like soils of differing acidity
• pH affects shampoo to softens or restores hair
• Affects soaps affect skin as well

Nuetralization Reactions

• They are a type of double displacement reaction with an acid and a base reacting to form products that have a neutral pH
• General form: acid + base -> water + ionic compound
• Applications: chemical spills and adding lime to ecosystems
• Antacids neutralize the acid in the stomach and contains magnesium hydroxide