Chemistry paper1

• Substances are made of atoms represented in the periodic table by a symbol

  • A compound contains two or more different types of atoms chemically bonded together
  • Atoms change what they're bonded to and how they're bonded through chemical reactions
• Word and chemical equations represent reactions

  • Atoms are not created or destroyed in any chemical reaction
  • Equations must be balanced to have the same number of each type of atom on both sides
• Mixtures are combinations of elements and compounds not chemically bonded

  • Filtration separates insoluble particles from a liquid
  • Crystallization leaves a solid dissolved in a liquid behind
  • Distillation separates liquids of a mixture based on boiling points
• States of matter: solid, liquid, gas

  • Melting or evaporating a substance requires energy to overcome forces of attraction
  • Physical changes, not chemical reactions
• Atoms have protons and neutrons in the nucleus, electrons in shells

  • Atomic number = number of protons
  • Atoms with different numbers of neutrons are isotopes
  • Periodic table organizes elements by properties and atomic weights
• Electrons fill shells with max 2, 8, 8, 2 electrons

  • Metals donate electrons, non-metals accept electrons
  • Group number indicates outer shell electrons
• Metallic bonding forms lattice of ions with delocalized electrons

  • Ionic bonding: metal donates electrons, non-metal accepts
  • Ionic compounds have high melting points, conduct electricity in solution
• Covalent bonding: non-metals share electrons to form molecules

  • Simple molecular structures have weak intermolecular forces
  • Giant covalent bonding forms giant molecules like diamond and graphite
• Graphene is a single layer of graphite

  • Fullerenes are 3D structures of carbon atoms
  • Nanoparticles are structures between 100 and 2,500 nm in size
• Total mass is conserved in a chemical reaction

  • Atoms are not created or destroyed in reactions
• Total mass of all substances is conserved in a chemical reaction
• Atoms that go in must come out, so equations must be balanced
• If a compound, add up relative atomic masses to get relative formula mass
• One mole of a substance has a mass equal to its relative atomic or formula mass
• Moles can be calculated using the formula: moles = mass / RAMs
• In a reaction, the ratio of moles of one substance to another is called stoichiometry
• Moles can be used to predict the mass of a product in a reaction
• Percentage yield tells us how much product is actually made compared to the theoretical maximum
• Atom economy is the efficiency of mass in a reaction
• One mole of any gas occupies a volume of 24 dm^3 at room temperature and pressure
• Metals vary in reactivity, more reactive metals displace less reactive metals in reactions
• Acids react with metals to produce salts and hydrogen gas
• The pH scale is logarithmic, with lower pH values indicating higher acidity
• Strong acids completely dissociate in solution, while weak acids only partially dissociate
• Titrations are used to determine the concentration of acids or alkalis
• Electrolysis involves the movement of ions in a solution or molten compound under the influence of an electric current
• Energy changes in reactions can be exothermic (energy released) or endothermic (energy absorbed)
• Activation energy is the energy required to start a reaction
• Bond energies can be calculated by summing the energies needed to break bonds and the energies released when new bonds are formed
• Cells or batteries contain chemicals that produce a potential difference to power electrical appliances
• Atoms cannot be broken down or split into smaller bits by chemical means
• A compound is two or more types of atoms chemically bonded together
• A mixture has different types of atoms or compounds not chemically bonded together
• Ways to separate mixtures:

  • Chromatography: water drawn up paper drags particles with it, lighter particles end up higher
  • Filtration: removes insoluble particles like sand from water
  • Distillation: separates a solute from a solvent like salt from water by evaporating and recondensing
• An atom has a nucleus with neutrons and protons, and electrons orbiting around

  • Protons have a charge of +1, electrons have a charge of -1, neutrons are neutral
  • Atoms must have the same number of protons as electrons to be neutral
• Periodic table:

  • 8 main columns, each column tells how many electrons are in the outer shell
  • Rows indicate the number of electron shells
  • Elements to the left are metals, electron donors
  • Elements to the right are nonmetals, electron acceptors
  • Group 1: alkali metals, get more reactive down the group
  • Group 7: halogens, get less reactive down the group
  • Group 8 or 0: noble gases, very unreactive
• Chemical bonding:

  • Ionic bonding: metals donate electrons to nonmetals, forming positive and negative ions
  • Covalent bonding: nonmetals share electrons to fill outer shells
  • Simple covalent bonding: small molecules formed by sharing electrons
  • Giant covalent bonding: continuous covalent bonds forming large structures like diamond, graphite
  • Metallic bonding: electrons become delocalized in a sea of ions, allowing for conductivity
  • Polymers: long chains formed by joining monomers
• History of the periodic table:

  • Dalton ordered elements by weight
  • Newlands grouped elements with similar properties every eighth element
  • Mendeleev arranged elements in columns and rows
• Chemical changes:

  • Metal and oxygen make a metal oxide (oxidation)
  • Metal or metal oxide with water make a metal hydroxide (alkali) and hydrogen gas
  • Acid and metal hydroxide make a salt and water (neutralization)
  • Thermal decomposition: heat breaks down compounds like copper carbonate into copper oxide and carbon dioxide
  • Displacement reactions: more reactive metal displaces less reactive metal in a compound
  • Rust: iron reacts with oxygen or water to form iron oxide
• Quantitative chemistry:

  • Atoms are not created or destroyed in chemical reactions
  • Chemical reactions must be balanced to ensure conservation of atoms