Chemistry 1

• Atoms are the tiny particles that everything is made up of-they have a radius of about 0.1 nanometer (that's 1 x 10 metres). Atoms are so tiny that a 50p piece contains about 77 400000000000000 000 000 of them
• Atom models


  • There are quite a few different (and equally useful) models of the atom-but chemists tend to like the nuclear model best. The nuclear model shows atoms as having a small nucleus surrounded by electrons
• The nucleus is in the middle of the atom. It contains protons and neutrons. Protons are positively charged. Neutrons have no charge (they're neutral). So the nucleus has a positive charge overall because of the protons. But size-wise it's tiny compared to the rest of the atom-the radius is 1 x 10"m that's about 1/10 000 of the size of an atom
• The electrons move around the nucleus. They're negatively charged. They're tiny, but they cover a lot of space. They occupy shells around the nucleus. Electrons don't have much mass at all compared to protons and neutrons, so nearly all of the mass of an atom is located in the nucleus
• Electrical charge


  The number of protons always equals the number of electrons in an atom. The charge on the electrons (-1) is the same size as the charge on the protons (+1) but opposite. This means atoms have no charge overall-they are neutral
• If some electrons are added or removed, the atom becomes charged and is then an ion. For example, an ion with a 2-charge has two more electrons than protons
• Elements


  Atoms can have different numbers of protons, neutrons and electrons. It's the number of protons in the nucleus that decides what type of atom it is
• There are about 100 different elements-quite a lot of everyday substances are elements. For example, copper, iron, aluminium, oxygen and nitrogen are all elements
• Nuclear symbols


  A nuclear symbol of an atom is the chemical symbol for the element with two numbers by it. The smaller (bottom) number is the atomic number. This is the number of protons, which conveniently also tells you the number of electrons. The larger (top) number is the mass number. This is the total number of protons and neutrons
• Isotopes


  Isotopes are different forms of the same element, which have the same number of protons but a different number of neutrons. This means they have the same atomic number but a different mass number
• Relative atomic mass


  Many elements have more than one isotope. This means when referring to the masses of elements, relative atomic mass (A) is used. This is an average mass taking into account the different masses of isotopes that make up the element, and how abundant each isotope is (how much there is of it). This means it's not always a whole number
• Compounds are substances formed from two or more elements. The atoms of the different elements are held together by chemical bonds, either by losing, gaining or sharing electrons
• Ionic bonding


  Metals and non-metals react to form compounds made of ions. The metal atoms lose electrons to form positive ions and the non-metal atoms gain electrons to form negative ions. The opposite charges (positive and negative) of the ions mean that they're strongly attracted to each other
• Covalent bonding


  A compound formed from non-metals usually consists of molecules. Atoms share electrons with other atoms-this is called covalent bonding
• The properties of a compound are totally different from the properties of the original elements
• Once a compound has been formed the elements can't be separated by physical processes. The only way to reform the elements is by more chemical reactions
• Word equations


  Word equations show what happens in a chemical reaction using the full names of the substances involved. They show the reactants (the substances that react together) and the products (the substances that are made in a reaction)
• Symbol equations


  Symbol equations show exactly the same as the word equation but using chemical symbols and formulas. However, when balanced correctly they also show the ratio of the amounts of substances involved in the reaction
• There must always be the same number of atoms of each element on both sides of an equation. This is called balancing the equation
• A mixture is made up of separate substances which, unlike in a compound, aren't joined together with chemical bonds
• Air


  • Nitrogen
  • Oxygen
  • Argon
  • Carbon dioxide
• Properties of a mixture

  Just a mixture of the properties of the separate parts - the chemical properties of a substance aren't affected by it being part of a mixture
• A mixture of iron powder and sulfur powder will show the properties of both iron and sulfur
• Physical methods of separation

  • Chromatography
  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
• Paper chromatography


  1. Draw a line near the bottom of a sheet of filter paper

  2. Spot the ink by placing a small amount on the line

  3. Place the sheet upright in a beaker of solvent

  4. The solvent will seep up the paper carrying the ink with it

  5. The different dyes will separate out and form spots in different places
• The number of spots on a chromatogram tells you the minimum number of different substances in the mixture
• Filtration


  1. Fold a piece of filter paper into a cone

  2. Place the filter paper point down into a filter funnel

  3. Pour the mixture containing the insoluble solid into the funnel

  4. The liquid will pass through the filter paper but the solid won't
• Soluble


  A solid that can be dissolved
• Evaporation


  1. Pour the solution into an evaporating dish

  2. Place the dish on a tripod and gauze with a Bunsen burner underneath

  3. Slowly heat the solution, the solvent will evaporate and the solid will start to form
• Crystallisation


  1. Place an evaporating dish on a tripod with a gauze mat and Bunsen burner underneath

  2. Pour the solution into the dish and gently heat it

  3. Once crystals start to form, remove from heat and leave to cool

  4. Filter the crystals out and leave to dry
• Crystallisation


  1. Place an evaporating dish on top of a tripod with a gauze mat

  2. Pour the solution into the evaporating dish and gently heat it

  3. Once some of the solvent has evaporated, or when you see crystals start to form, remove the dish from the heat and leave the solution to cool

  4. The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution

  5. Filter the crystals out of the solution, and leave them in a warm place to dry
• Crystallisation


  Takes more time than evaporation, however it can produce nice crystals, that would decompose if heated
• Evaporation


  Quicker than crystallisation
• Simple distillation


  1. The mixture is heated

  2. The component of the mixture that has the lowest boiling point evaporates

  3. The vapour rises and passes into the condenser, where it is cooled and condenses (turns back into liquid)

  4. Components of the mixture with higher boiling points are left behind in the flask
• Simple distillation


  • Used to separate out a liquid from a mixture
  • Not suitable when the boiling points of the substances are close to each other
• Fractional distillation


  1. Place the mixture in a flask, attach a fractionating column on top and heat it

  2. The different liquids will all have different boiling points- so they will evaporate at different temperatures

  3. The liquid with the lowest boiling point evaporates first and condenses in the condenser

  4. Liquids with higher boiling points might also start to evaporate but will only get part of the way up the column before condensing and running back down
• Fractional distillation


  • Used for separating a mixture of different liquids when the boiling points are close together
  • Commonly used in industry to separate crude oil into different groups
• Distillation is used to separate mixtures that include a liquid
• There are two kinds of distillation: simple and fractional
• Simple distillation is used to separate out a liquid from a mixture