Chapter 1

• All substances are made of atoms. An atom is the smallest part of an element that can exist
• Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen, Na represents an atom of sodium.
• An element is a substance with only one type of atom. Elements are listed in the periodic table.
• There are about 100 different elements. Elements can be classified as metal or non-metal depending on their properties.
• The columns in the periodic table are called groups and contain similar elements.
• The rows in the periodic table are called periods. Elements show a gradual change in properties across a period
• An element on the periodic table will be displayed like figure 1. In it you will find the following:

  • The elemental symbol. The first letter is always a capital, others are lower case

  • The greater of the two numbers is the ATOMIC MASS and is equal to the combined mass of the protons and neutrons in the atom.

  • The smaller of the two numbers is the ATOMIC NUMBER and is equal to the number of protons (and electrons) in the atom.

  
• Some elements combine through chemical reactions to form compounds
• Compounds are made from two or more different elements (types of atoms) combined together in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed, e.g CO2
• Compounds have different properties from the elements they are made from.
• Compounds can only be separated into elements by chemical reactions.
• A chemical equation shows which substances react and what products they make
• Reactants → Products
• The law of conservation of mass tells us that in chemical reactions matter is not destroyed or created. So the number of atoms and type of atoms will be the same either side of the equation.
• State symbols can be included in equations, these are always shown in brackets:

  o (s) Solid

  o (l) liquid

  o (g) gas

  o (aq) aqueous
• A mixture consists of two or more elements or compounds not chemically combined together.
• The chemical properties of each substance in the mixture are unchanged.
• Mixtures can be separated by physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography. These physical processes do not involve chemical reactions
• Type of mixture separated:

  Soluble solid dissolved in a liquid (usually water) e.g. salty water

  Explanation:

  Liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid.

  A) Thermometer

  B) Liebig condenser

  C) Water in

  D) Water Out

  E) Round bottomed flask

  F) Heat

  
• Soluble liquids with different boiling points e.g. crude oil

  The fractionating column has a temperature gradient and is hotter at the bottom than at the top

  A) Fractionating Column

  B) Liebig condenser

  
• Fractional Distillation explanation:

  When a mixture of soluble liquids is heated all

  liquids are evaporated. The liquid with the lowest boiling point,

  however, forms the greatest percentage of vapour. As the

  vapour moves up the fractionating column it becomes more

  rich with the component that has the lowest boiling point. This

  is due to the vapour mixture condensing and evaporating as it

  moves up the column.

  A thermometer measures the temperature of the fractions

  before they condense. The liquid with the lowest boiling point

  will be the first ‘fraction’ to collect.
• Separates an insoluble solid suspended in a liquid

  (usually water) e.g. sand and water.

  A) Residue

  B) Filter funnel

  C) Filter paper

  D) Filtrate

  
• Filtration explanation:

  The insoluble solid (called residue) gets caught in

  the filter paper, because the particles are too big

  to fit through the holes in the paper.

  The filtrate is the substance that comes through

  the filter paper.
• Atoms have a small central nucleus made up of protons and neutrons around which there are electrons.
• In an atom, the number of electrons is equal to the number of protons in the nucleus.
• Atoms have no overall electrical charge.
• All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons.
• Most of the mass of an atom is in the nucleus
• The number of protons in an atom is called its atomic number (proton number). Atoms are arranged in the modern periodic table in order of their atomic number (proton number)
• The total number of protons and neutrons in an atom is called its mass number
• To work out the number of neutrons in an atom subtract the atomic number from the mass number
• Study and fill in the diagram:

  A) nucleus

  B) protons

  C) neutrons

  D) Energy shells

  E) electrons

  F) Protons

  G) positively charged

  H) Electrons

  I) negatively

  J) Neutrons

  K) no

  
• Atoms are very small, having a radius of about 0.1 nm (1x 10-10 m). The radius of a nucleus is less than 1/10000 of that of the atom (about 1 x 10-14 m).
• Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element. Isotopes of an element have the same chemical properties because they have the same electronic structure.
• The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element.
• R.A.M = Σ (isotopic mass x % abundance)/100
• Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level.
• The electrons in an atom occupy the lowest available energy levels . The first energy level can hold a maximum of 2 electrons, the 2nd and 3rd can hold up to 8.
• All elements in the same period have the same number of energy shells.
• All elements in the same group have the same number of electrons in the outer shell.