chemistry

• Atoms consist of electrons in outer shells, protons in the nucleus with a mass of one and a charge of plus one, and neutrons in the nucleus with a mass of one and a charge of zero
• The atomic number of an element tells us the number of protons and electrons in an atom, while the mass number is the number of protons plus the number of neutrons
• Isotopes have the same number of protons but a different number of neutrons, affecting their mass numbers
• The mass of elements like Chlorine with .5 mass is due to the relative abundance of isotopes, such as Chlorine 35 and Chlorine 37
• The Periodic Table provides information on elements, their atomic numbers, mass numbers, and electron configurations
• Groups in the Periodic Table indicate the number of electrons in the outer shell, while periods relate to the number of electron shells an element has
• Metals lose electrons to form positive ions, while non-metals gain electrons to form negative ions
• Ionic bonding involves the transfer of electrons from a metal to a non-metal, forming ions with charges based on their group number
• In an ionic bond like magnesium oxide, electrons are transferred from magnesium to oxygen, creating ions with opposite charges
• Atoms have protons with a positive charge and electrons with a negative charge
• In an atom, positive charges and negative charges cancel each other out, resulting in a neutral charge
• When an atom becomes an ion, it can gain or lose electrons, leading to a positive or negative charge
• Ionic bonding involves a giant ionic lattice structure, resulting in high melting and boiling points, and conductivity when molten or dissolved
• Covalent bonding is the sharing of electrons between two non-metals, leading to low melting and boiling points, and non-conductivity
• Simple covalent compounds like water or methane have small structures, low melting points, and do not conduct electricity
• Giant covalent compounds like diamond or graphite have high melting points, do not conduct electricity, and do not dissolve
• Diamond is incredibly hard and made of pure carbon with each carbon making four bonds
• Graphite conducts electricity due to a spare electron floating between sheets of carbon atoms
• Fullerenes, like carbon nanotubes or Buckminster fullerenes, are incredibly hard and have potential applications in various fields
• Polymers with cross-links are rigid and burn upon heating, while those without cross-links melt upon heating
• Metals have positive ions in a sea of delocalized electrons, allowing them to conduct electricity and heat well
• Alloys, like metals, have positive ions and delocalized electrons but may also contain other elements, making them harder than pure metals
• Balancing chemical equations involves recalling formulas, determining products, and balancing the number of atoms on each side of the equation
• To balance the equation for the reaction between hydrochloric acid and magnesium, you need to add another HCl to have two hydrogens and two chlorines on each side
• Balancing the equation for the reaction between water (H2O) turning into hydrogen gas (H2) and oxygen gas (O2) involves adding another H2O to balance the number of hydrogens and oxygens on each side
• The relative formula mass (MR) is calculated by adding the relative atomic masses (AR) of the elements involved in the compound
• The empirical formula is the lowest ratio of all the elements in a compound, calculated by dividing the mass percentage of each element by its atomic mass and then simplifying the ratios
• A mole is the unit for the amount of a substance, equal to 6.022 x 10^23 atoms, ions, or molecules
• When working with limiting reactants in a chemical reaction, ensure that the reactant you don't want to limit the reaction is in excess
• State symbols in chemical equations indicate the physical state of the substances involved: (S) for solid, (L) for liquid, (G) for gas, and (aq) for aqueous
• Elements are pure substances, while compounds consist of two or more different things chemically bonded together
• If a substance is pure, it will melt at its melting point, while a mixture will bear out on a range of melting points
• To separate compounds, chromatography can be used to achieve beautiful separations
• To separate mixtures, different methods can be employed:

  • Distillation: separates substances by boiling points
  • Evaporation: removes the liquid, leaving solids dissolved in it
  • Filtration: separates large particles of solid in a liquid
  • Fractional distillation: separates substances at different boiling points
• Desalination is the process of removing salts from water to make it suitable for drinking
• To make water safe to drink, dirt, bacteria, and unwanted minerals like salt need to be removed
• On the pH scale, a pH of 1 is acidic, 7 is neutral, and 14 is an alkali
• Strong acids like hydrochloric acid, nitric acid, and sulfuric acid freely dissociate into hydrogen ions and other ions, while weak acids only partially dissociate
• In electrolysis, ionic compounds need to be molten or dissolved to conduct electricity
• Electrolysis involves positive and negative electrodes, with a light bulb used to check if electricity is flowing