Science - Chemistry Unit Term 2 Year 8

• Solid


  • Have a fixed shape and volume
  • Cannot flow
  • Cannot be compressed
• Solids


  A state of matter that has a fixed shape and volume. Solids do not flow and cannot be compressed.
• Liquids


  A state of matter that flows and takes the shape of its container. Liquids have a fixed volume, but can change shape easily. Examples include water, oil, and alcohol.
• States of matter


  The three basic forms of matter, which are solids, liquids, and gases. Solids, liquids, and gases have different physical properties and behaviors.
• Gases


  A state of matter that flows and takes the shape of its container. Gases do not have a fixed volume and can expand or contract to fill the container. Examples include air, carbon dioxide, and helium.
• Density


  A measure of the amount of mass per unit of volume. It is calculated by dividing the mass of an object by its volume.
• Solids and density


  In solids, particles are closely packed and have little movement. This results in a high density, as there is a large amount of mass in a small volume.
• Liquids and density


  In liquids, particles are close together but can move past each other. This results in a lower density compared to solids, as there is less mass in a given volume.
• Gases and density


  In gases, particles are widely spaced and have a lot of movement. This results in a very low density, as there is very little mass in a large volume.
• Density formula


  The formula for density is density = mass / volume. This formula can be used to calculate the density of an object if you know its mass and volume.
• Density units


  Density is measured in units such as grams per cubic centimeter (g/cm^3) or kilograms per cubic meter (kg/m^3).
• Mass units


  Mass is the amount of matter in an object, and is measured in units such as grams (g) or kilograms (kg).
• Volume units


  Volume is the amount of space occupied by an object, and is measured in units such as cubic centimeters (cm^3) or cubic meters (m^3).
• DMV acronym


  The DMV acronym can be used to help remember the formula for density. It stands for Density = Mass / Volume, and can be applied to calculate the density of any object, as long as you know its mass and volume.
• Mixture


  2 or more different types of particles or substances
• Mixture


  A mixture is a combination of two or more pure substances in which each pure substance retains its individual chemical properties. Mixtures can be composed of solids, liquids, or gases.
• Suspension


  2 or more types of particles… (large sized solid particles floating between liquid particles)
• Element


  Science describes an element as a pure substance made of only 1 type of atom that can not be broken down further into other substances. For example, hydrogen (H) and oxygen (O) are elements, but water ( H 2 O ) which is made of hydrogen and oxygen is NOT.
• Compound


  A compound is a material formed by chemically bonding two or more chemical elements. The type of bond keeping elements in a compound together may vary: covalent bonds and ionic bonds are two common types.
• Compound


  2 or more types of elements chemically combined into fixed ratios.
• Atoms


  An atom consists of a central nucleus that is surrounded by one or more negatively charged electrons. The nucleus is positively charged and contains one or more relatively heavy particles known as protons and neutrons. Atoms are the basic building blocks of matter.
• Compounds

  • When two (or more) different elements are chemically joined together they form compounds.

  
• Compounds


  Pure substance composed of two or more different elements joined by chemical bonds.

  • Has a chemical formula
  • Can only be separated by chemical means, not physical
• The difference between a compound and a molecule

  • a molecule is formed when two or more identical atoms join together chemically. eg O2
  • a compound is a molecule that contains at least two different elements Eg. C
• Mixtures


  A mixture contains two or more pure substances that are not chemically combined. They can be separated.

  
• Mixtures:

  • A combination of two or more pure substances that are not chemically combined
  • Each item retains its properties
  • They can be separated physically
  • Tap water contains many pure substances, for example, which can be removed by distillation
• Elements, Compounds and Mixtures

  iron and sulphur mixture & iron + sulfer = iron sulfide

  
• Carbon Example - Atoms and Elements


  Carbon is an element of which diamonds are composed.

  Carbon contains 6 protons (as you can see from the number above ‘C’)

  However, there are different types of carbon, based on the number of neutrons it contains. (Just like there are different types of potatoes!)

  We call the overarching concept carbon the ‘element’ and each of the different variety an ‘atom’.
• atoms and elements

  ELEMENTS vs. ATOMS

  
• How we represent elements - Atoms and Elements

  • Elements are made up of identical atoms.
  • Some elements exist in pairs or more (Pairs of Atoms)

  
• Atoms and Elements


  Examples of Elements (read through image)

  
• Chemical Symbols:

  • Li = Lithium
  • Na= Sodium
  • Cr= chronium
  • Au= gold
  • P = phosphorus
• Periodic table


  Scientist display all the known elements and their symbols in a table called the Periodic Table.

  The Numbers are in ascending order.

  The colours represent the group such as metal, non-metal, alkali metal, metalloi, etc. -Not Important for Year 8
• Chemical Word Equations


  Chemical equations are written in form of:

  • Reactants->Products

  Let’s look at a proper chemical reaction:

  • Magnesium + Oxygen-> Magnesium Oxide

  In this case, two reactants make one product through a chemical reaction.
• Chemical Word Equations

  • A word equation is a written representation of a chemical reaction. It is an efficient way to describe chemical reactions.
  • It contains all the substances used and produced in the reaction

  
• Chemical Equations


  Eg.

  
  

  ”calcium carbonate + sulfuric acid -> calcium sulphate + carbon dioxide + water”

  
  

  is equal to

  
  

  CaCO3 + H2SO4 -> CaSO4 + CO2 + H2O
• Chemical Equations helps us identify:

  • what atoms are involved
  • how the reactants are rearranged to form new products
• Chemical Equations: A chemical equation is a mathematical representation of a chemical reaction.
• The Law of Conservation of Mass


  We notice the number of elements does not change through chemical reaction.

  ”Atoms cannot be created if destroyes during a chemical readtion”

  But you can rearrange them by breaking bonds and forming new ones.
• Aqueous solution:


  A solution of a substance dissolved in water.