reactions

• a chemical change is also called a chemical reaction
• chemical changes mean that you end up with different substances from the ones you started with
• physical changes is when the physical properties change but the substances stay the same
• a physical change is when no new substances form and involves a change of physical properties such as position, shape, size or state (solid, liquid, gas)
• a chemical reaction is when new substances form. typical signs include release of light or sound, formation of a new gas, change in colour, disappearance of a solid, formation of a new solid or change in temperature
• an atom is the smallest particle of an element
• a molecule is a group of atoms bonded together
• a chemical bond is an attractive force that holds two atoms together
• a mixture is a combination of substances that can be physically seperated
• a chemical reaction is the change in matter that forms one or more new substances
• chemical reactions include substances that may be either elements or compounds
• elements include any of the basic substances on the periodic table, such as oxygen (O), iron (Fe) and gold (Au)
• elements are made up of only one type of atom
• compounds are made up of two or more different types of atoms bonded together, such as carbon dioxide (CO2) and sodium chloride (NaCl)
• the chemical formula of a compound showcases the relative numbers of atoms of each element
• in chemical reactions, the substances that react with each other are called reactants
• the new substances formed by a reaction are called products
• some chemical reactions have only one reactant, while others have only one product. for example, the reaction between magnesium and oxygen has only one product: magnesium oxide
• during a chemical reaction, chemical bonds are broken and chemical bonds are formed
• chemical reactions can involve bonds being broken, allowing the atoms to be arranged in a new way
• chemical reactions can involve new bonds being formed to create a new substance
• there are different elements present after a chemical reaction than before it
• chemical reactions produce new substances but they cannot produce new elements. the atoms of each element are simply rearranged
• in chemical reactions, when a compound is broken down into elements, those elements were already present in the compound. for example, water contains the elements hydrogen and oxygen
• reactants → products
• the two sides of a chemical equation have an equal number of atoms of each element. this is because a chemical reaction simply re-arranges the atoms in the reactants to form the products
• in a chemical reaction, no atoms are created or destroyed so the number of atoms stay the same
• symbol equations have the same basic structure as word equations but provide more information
• -O

  monoxide
• -O2

  dioxide
• -O3


  trioxide
• -OH

  hydroxide
• -Cl

  chloride
• -F

  fluoride
• -Br

  bromide
• -S

  sulfide
• -CO3


  carbonate
• -NO3

  nitrate
• a composition reaction is one that has a single product
• composition reaction


  A + B → AB