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.