Year 9 Chemistry Review Flashcards

Atom, Element, Compound, Mixture, Molecule

Atom:
- The smallest particle that makes up matter.
- Example: A carbon atom.
Element:
- A substance made from only one type of atom.
- Examples: Hydrogen, Oxygen, Magnesium.
- There are 118 different types of elements found on the periodic table.
Compound:
- A substance containing two or more elements chemically bonded together.
- Example: Carbon dioxide (CO2), which is made of a carbon atom bonded with two oxygen atoms.
Mixture:
- Contains two or more substances which are not chemically bonded and can be separated.
- Examples: Air, Sand and Water, Chocolate chip ice cream.
Molecule:
- A small number of non-metal atoms chemically bonded together.

Chemical Reactions and Equations

Chemical Reaction:
- Occurs when two or more substances combine to form new products.
- Atoms cannot be created or destroyed (Law of Conservation of Mass).
Conservation of Mass:
- Mass of Reactants = Mass of Products
- Example: 2Mg + O2 \rightarrow 2MgO
- Ensures there is an equal number of atoms on either side of the equation.
Word Equation:
- The reactants and products of a chemical reaction are shown using words.
- Example: Magnesium + Oxygen → Magnesium oxide
Balanced Symbol Equation:
- Uses chemical symbols to represent a reaction ensuring the number of atoms is the same on both sides
- Example: 2Mg + O_2 \rightarrow 2MgO
Chemical Formula:
- Shows the number and ratio of atoms in a substance using subscripts.
- Examples: H2, Li2O, Cl2, NaCl, H2O

Atomic Structure

Atomic Structure:
- Describes the particles which make up an atom and where they are located.
Subatomic Particles:
- Particles smaller than an atom (e.g., proton, neutron, and electron).
Proton:
- Positively charged particle found in the nucleus of the atom with a mass of 1.
Neutron:
- A neutral particle found in the nucleus of an atom with a mass of 1.
- The number of neutrons in an atom may differ.
Electron:
- Negatively charged particle which orbits the nucleus of an atom.
- Electrons have very little mass.
Atomic Number:
- The number of protons in an atom.
- Also called proton number.
- Always stays the same for the atom of an element.
- Atomic number is always the smaller number.
- Number of protons = atomic number.
- Number of electrons = number of protons in a neutral atom.
Mass Number:
- The mass number is equal to the number of protons and neutrons in the nucleus of an atom.
- Number of neutrons = mass number – atomic number.
- Example: For C¹², 12 - 6 = 6 neutrons.

Ions and Bonding

Ion:
- An atom that has lost or gained electrons.
- Metals lose electrons to form positive ions.
- Non-metals gain electrons to form negative ions.
Simple Molecule:
- A small number of non-metal atoms chemically bonded by covalent bonds.
Lattice:
- A lattice is formed when there are a large number of atoms organized in a regular pattern.
- Ionic compounds form a lattice when solid.
- Some non-metals form lattices.
Ionic Bond:
- An electrostatic attraction between oppositely charged ions.
- Ionic bonds are always formed between a metal and a nonmetal.
Covalent Bond:
- A single covalent bond is formed when a pair of electrons is shared between two atoms.
- Covalent bonds are strong. The nucleus of each atom is attracted to the shared electrons.
Giant Covalent Structure:
- A giant covalent structure is formed when a large number of non-metal atoms are joined together by covalent bonds to form a lattice.
- Examples include graphite, diamond, and silicon dioxide.
Dot and Cross Diagram (Ionic Bonds):
- The diagram should show:
  - Brackets around each ion.
  - The charge of each ion.
  - The electron configuration of the ion.
Dot and Cross diagram (Covalent):
- The diagram should show:
  - Electrons shared between atoms.
  - Each atom should have a full outer shell including the shared electrons.
  - One pair of electrons is a single bond.
  - Two pairs of electrons form a double bond.
Delocalised Electrons:
- Chemical bonding in metals and graphite leads to the outer shell electrons being free to move throughout the structure of the materials.
- When the electrons can move freely they are called delocalised. This means they can conduct heat and electricity.

Salts and Separation Techniques

Salt:
- A salt is an ionic compound which usually forms crystals when solid.
- Salts are often formed in reactions with acids.
- Examples of reactions which form salts:
  - Metal + Acid → salt + hydrogen.
  - Acid + Base → salt + water.
  - Metal carbonate + acid → salt + water + carbon dioxide.
Naming Salts:
- The acid used to make the salt will determine the name of the salt:
  - Hydrochloric acid forms chloride.
  - Sulfuric acid forms sulfate.
  - Nitric acid forms nitrate.
Soluble/Insoluble:
- A substance is soluble if it can dissolve in water.
- A substance is insoluble if it cannot dissolve in water.
- A precipitate is an insoluble solid formed in a chemical reaction.
Filtration:
- Method of removing an insoluble solid from a liquid.
Crystallisation:
- A soluble solid can be separated from a solution if the water is allowed to evaporate from the solution.
- The solution can be heated or allowed to evaporate overnight.
Writing Ionic Formula:
- Example: Calcium Nitrate
  - Calcium ion: Ca^{2+}
  - Nitrate ion: NO_3^-
  - Formula: Ca(NO3)2
  - Overall charge: (2+) + (-)+(-) = 0
  - The overall charge of the compound is zero.
Pure Substance:
- A pure substance consists only of one element or one compound.
Mixture:
- A mixture consists of two or more different substances, not chemically joined together.
Impurity:
- Both pure substances and mixtures can be considered impure if they contain impurities, an unwanted substance.
Filtrate:
- The liquid after it has been filtered.
Residue:
- The solid that remains in the filter paper.