YEAR 10 C2&3 CHEM

• A pure substance is a SINGLE element or compound.
• Mr is the sum of relative atomic masses of the atoms in the numbers shown in the formula.
• Sum of Mr of reactants = sum of Mr of products
• Relative atomic mass is the average mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12.
• Relative molecular mass is the average mass of a molecule compared to 1/12th the mass of an atom of carbon-12
• Formulations are
• Many products are complex mixtures in which each chemical has a purpose
• Formulations are made by mixing components in carefully measured quantities to produce a product with the required properties.
• Examples of formulations are: Paint, soap, perfume, and detergent
• Most metals used everyday are alloys. Pure copper, gold, iron and aliminium are too soft and are mixed with similar metals to make them harder.
• Filtration is used to separate a insoluble salt/solute and liquid from a solution.
• Crystillisation is used to separate a soluble solid from a solution.
• Simple distillation is used to separate a solvent from a solution. Dissolved solute has a higher boiling point than the solvent
• Fractional distillation is used to separate a pure liquid from a mixture of liquids with different boiling points. The temperature is gradually raised and every liquid is collected and condensed.
• Chromatography is used to separate mixtures of substances and give information to help identify said substances.
• Mobile phase= liquid (water or ethanol for example)
• Stationary phase= chromatography paper
• Rf value= distance moved by substance/distance moved by solvent
• Rf values can be used to help identify compounds
• Metals= elements that form positive ions (in aqueous solutions also).
• Non-metals= elements that form negative ions.
• Physical changes are reversible and the particle size of the substance remains the same.
• Chemical changes are irreversible and the properties of new substance are different from original. Number of particles can change.
• Dot and cross diagrams don't show the 3D lattice structure of an ionic compound or giant compound.
• Ball and stick diagrams fail at indicating the movement of electrons.
• Ball and stick diagrams also make gaps between atoms bigger than in reality.
• in Ionic bonding, electrons in the outer shell of the metal atom are transferred to the nonmetal
• Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions.
• Ionic compounds have regular structures (giant ionic lattices).
• Ionic compounds have high melting and boiling points as a lot of energy is required to break strong electrostatic bonds.
• When dissolved in water or melted, ionic compounds conduct electricity as the electrons are free to move and carry current.
• Simple molecules are held together by strong covalent bonds.
• Simple molecule particles are atoms that share electrons.
• Covalent bonding occurs in nonmetallic elements and in compounds of nonmetals.
• Covalently bonded substances may consist of small molecules like HCl, Oxygen, Hydrogen.
• Substances that consist of simple molecules are usually gases or liquids that have low melting and boiling points.
• Substances that consist of simple molecules have weak intermolecular forces between the molecules, meaning less energy is requiured to break them apart. The intermolecular forces are broken during melting/boiling, not the covalent bonds
• The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting/boiling points.
• Substances that consist of simple molecules don't conduct electricity, as they don't have an overall electric charge.
• Giant covalent structures are made of strong covalent bonds.