C11

C11

1. C11.1

   • All substances are made up of atoms.
     • Atoms can be found on their own, or in groups. When they're in groups, this is called a molecule.
     • Atoms are made of protons, neutrons and electrons.
       • Protons and neutrons are gathered in a cluster at the centre of the atom, whilst electrons orbit the atom in layers called shells.
         • Electrons have a negative charge, where as protons have a positive charge and neutrons are neutral.
           • An atom contains the same amount of protons and electrons, so it is not charged.
             • The amount of protons in an atom is known as the atomic number.
               • The mass number is the amount of protons and neutrons in the atom.
                 • To find out the number of neutrons, you must subtract the mass number and the atomic number.
   • A substance which contains only one type of atom is called an element.
     • There are about 100 different elements, which can be found on the periodic table.
   • A mixture is a group of atoms which are not chemically bonded.
   • A compound is made up of more than one type of atom which have been chemically bonded.
   • An atom can have 2 electrons in its innermost shell, and up to 8 electrons in its other shells. In order to have electrons in outer shells, the inner shells must first be full.

2. C11.2

   • Rows of elements are called periods. Elements in the same period have the same amount of shells.
     • Columns of elements are called groups. Elements in the same group have the same amount of electrons in their outer shell, and all have the same amount of reactivity.
       • Elements in group 1 are called the alkaline metals, and elements in group 0 are called noble gases.
         • The alkaline metals are the most reactive elements on the periodic table.
         • The noble gases are almost inert..

3. C11.3

   • The periodic table can be divided into 3 groups:
     • A metalloid is an element with some qualities of a metal, and some qualities of a non-metal.
       • When you go down a group and to the left of a period, the elements get more and more reactive.
   • The alkali metals are so reactive that they are rarely found in nature, and have to be stored in oil to prevent them from reacting with the air.
     • They are very soft and can be easily cut. They react with water to form alkaline compounds. They have a low density and low melting and boiling points.
       • Alkali metals all have 1 electron in their outer shell.
         • More reactive metals have more shells, because the further away an electron is from the nucleus of the atom, the easier it is for the electrons to be lost.
           • alkali metal + water -> alkali metal hydroxide + hydrogen
             • alkali metal + oxygen -> alkali metal oxide
   • The noble gases all form colourless gases at room temperature.
     • Helium only has 2 electrons in it's outer shell, but all the other noble gases have 8.

4. C11.4

   • A chemical reaction is a change that takes place when one or more substances (called reactants) form one or more new substances (called products)
     • Many chemical reactions are are irreversible changes. You can spot this by a colour change, a precipitate (solid) forming, an odour being produced, or energy being produced (which is shown by fizzing or burning.
     • In a chemical reaction, electrons are either shared, lost or gained.
       • An ion is a charged atom
         • Ionic bonding takes place between a metal and a non metal. Electrons are taken, not shared. The metal atoms will lose electrons and become positively charged, and the non-metal atoms will gain electrons and become negatively charged. The ionic bond is the attraction between positive and negative ions.
       • In covalent bonding, electrons are shared. It only occurs between non-metals. Each shared pair is a covalent bond.
       • Metallic bonding occurs between metals. Metals lose electrons, which become delocalised. Because of these free-moving electrons, metals can conduct heat and electricity well. Metallic bonding is the attraction between positive metal ions and delocalised electrons.
     • In a chemical reaction, the mass doesn't change. This is because no atoms are made or destroyed, the reaction just changes how atoms are bonded together.

5. C11.5

   • In an ionic compound, the non metal will be negatively charged and the metal will be positively charged.

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