Chem topic 1

Chem topic 1

1. The structure of an atom

   • At the centre of an atom is a nucleus containing protons and neutrons. Electrons are arranged around the nucleus in energy levels or shells. At the centre of an atom is a nucleus containing protons and neutrons.
     • Both protons and electrons have an electrical charge. Both have the same size of electrical charge, but the proton is positive and the electron negative. The neutron is neutral.
       • The total number of electrons in an atom is always the same as the number of protons in the nucleus. This means atoms have no overall electrical charge.
         • particle relative charge proton= +1 neutron= 0 electron =-1

2. What the sub atomic particles are, their masses and charges.

   • The mass number of an atom is its total number of protons and neutrons. Isotopes are atoms of an element with different numbers of neutrons. The relative formula mass of a compound is found by adding together the relative atomic masses of all the atoms in the formula of the compound. The relative formula mass of a substance in grams is one mole of that substance.
   • Subatomic particles
     • Each atom consists of a nucleus containing protons and neutrons, with electrons arranged around it in energy levels.
     • Relative masses of subatomic particles
       • Name of particle Relative mass Proton= 1 Neutron= 1 Electron= Very small (1/1836)
   • Mass number and atomic number
     • The mass number of an atom is never smaller than the atomic number. It can be the same, but is usually bigger: The mass number of an atom is the total number of protons and neutrons it contains The atomic number of an atom is the number of protons it contains Notice that most of the mass of an atom is found in the nucleus.

3. Isotopes

   • The atoms of a particular element will all have the same number of protons. Their atomic number will be the same. However, the atoms of an element can have different numbers of neutrons - so their mass numbers will be different. Atoms of the same element with different numbers of neutrons are called isotopes. The different isotopes of an element have identical chemical properties. However, some isotopes are radioactive.
     • Chemical symbols
       • The full chemical symbol for an element shows its mass number at the top, and atomic number at the bottom. Here is the full symbol for carbon: C 12,6 It tells us that a carbon atom has six protons. It will also have six electrons, because the number of protons and electrons in an atom is the same. The symbol also tells us that the total number of protons and neutrons in a carbon atom is 12. Note that you can work out the number of neutrons from the mass number and atomic number. In this example, it is 12 – 6 = 6 neutrons.
         • Isotopes of hydrogen Most hydrogen atoms consist of just one proton and one electron, but some also have one or two neutrons.

4. Chemical equations and what subscripts and coefficients mean.

   • Subscripts in Chemistry: Notice the number 3 is written as a subscript, or a number that is smaller than the other text, and below the normal text line, in the formula for anhydrous aluminum chloride above. The concept of a multiplicity of atoms is conveyed by this use of a subscript.
     • You can also write the formula for Sucrose or table sugar, using chemical symbols and subscript numbers. There are 12 carbon atoms, 22 hydrogen atoms, and 11 oxygen atoms in sucrose – the chemical formula for table sugar looks like this: C₁₂H₂₂O₁₁.
   • Coefficients
     • You must understand both in order to read and to use chemical equations successfully. First: the coefficients give the number of molecules (or atoms) involved in the reaction. In the example reaction, two molecules of hydrogen react with one molecule of oxygen and produce two molecules of water.
   • Copper and oxygen reaction: getting a balanced equation Balanced symbol equations show what happens to the different atoms in reactions. For example, copper and oxygen react together to make copper oxide. Take a look at this word equation for the reaction: copper + oxygen → copper oxide Copper and oxygen are the reactants because they are on the left of the arrow. Copper oxide is the product because it is on the right of the arrow. If we just replace the words shown above by the correct chemical formulas, we will get an unbalanced equation, as shown here: Cu + O2 → CuO Notice that there are unequal numbers of each type of atom on the left-hand side compared with the right-hand side. To make things equal, you need to adjust the number of units of some of the substances until you get equal numbers of each type of atom on both sides. Here is the balanced symbol equation: 2Cu + O2 → 2CuO You can see that now there are two copper atoms and two oxygen atoms on each side. This matches w