Atomic structure and the periodic table
- A proton has a positive charge, an electron has a negative charge and a neutron is uncharged.
- Protons and neutrons have approximately the same mass of 1.
- Electrons have a mass about 1/2000 of a proton
- The top number of an element is the mass number or the nucleon number. The mass number is the number of protons + neutrons.
- The bottom number is the proton number which is the number of protons. The number of protons is always the same as the number of electrons.
- The elements in the periodic table are ordered with the proton number increasing. The proton number is also the atomic number.
- The number of electrons in the outer shell of an element is the same as the group number.
Atomic structure- Isotopes
An isotope is the same element but with a different number of neutrons.
They can be radioactive or non-radioactive.
- Radioisotopes can be used for radiotherapy and mineral analysis. Electrons are built up in shells with a maximum number of 2 electrons in the first shell and then 8 in the shells after. Valency electrons are where the element needs to gain or lose a certain number of electrons to get a full outer shell. For example 'Magnesium' has a valency number of 2. A full outer shell makes the element stable. Noble gases are unreactive because their outer shells are full.
- The relative atomic mass (RAM) of an element is the mass of an average atom of the element relative to a carbon-12 atom which weighs 12.00 units.
- The relative molecular mass is the sum of the relative atomic masses.
- To find the relative formula mass (Mr) of a compound, you just add together the relative atomic mass values for all the atoms in its formula.
In solids the particles are in a tight regular arrangement. They can vibrate.
In liquids the particles can move around each other.
In gases the particles are free to move.
Only liquid and gas particles diffuse. Diffusion is the spreading out and intermingling of liquids and gases.
The larger the molecular mass the greater the rate of diffusion.
Acids, bases, salts and ions
A mixture is made from different substances that are not chemically joined.
A compound contains two or more types of atom joined together.
An element contains just one type of atom.
Ions are formed by the gain or loss of electrons.
Ionic compounds are formed when group 1 and group 7 elements combine.
Ionic bonds can be formed between metallic and non-metallic elements.
Ionic bonds have a regular 3D lattice of alternative positve and negative ions.
Ionic substances have high melting points and boiling points and are soluble in water.
Molecules and covalent bonding
Atom = most fundamental unit of an element
Molecule = made up of one or more atoms (not necessarily different types of atoms)
Ion = electrically charged atom due to gain/loss of an electron
Ionic compounds conduct electricity in aqueous solutions or when molten.
Covalent compounds do not conduct electricity.
Simple molecular substances have low melting points and they may/may not be soluble in water.
Giant Molecules (macromolecules)
Graphite and diamonds are strong covalent structures.
Graphite can be used as a lubricant because the layers are held to other layers by weak forces so they can move.
Diamonds are used for cutting tools. Diamond is strong because each carbon atoms in a diamond is strongly bonded to 4 other atoms so it is fixed and the bonds are covalent and really strong.
Metallic bonding is a lattice of positive ions in a sea of electrons.
Acids, bases, salts and ions
Acids react with metals to form salts and hydrogen.
Acids react with hydroxides and basic oxides to form a salt and water.
Acids react with carbonates to form a salt, carbon dioxide and water.
pH can be measured using universal indicator, pH 7 is neutral (neither acid or alkaline)
The pH scale can describe the degree of acidity or alkalinity.
Acids and bases
An acid gives off protons (to water) when it reacts whereas a base accepts protons.
When dissolved in water, strong acids are completely ionised.
When dissolved in water, weak acids are only slightly ionised.
Salts can be made by the reaction of acids and metals, metal oxides, hydroxides and carbonates.
Filtration and crystallization are used to separate and purify salts by precipitation.
You can do a titration to make a salt. You will use dilute sulphuric acid. If you need pure salt crystals you cannot use indicator. Therefore you must do the experiment twice.
Fill a burette with sulphuric acid. Run it through to get rid of air bubbles. Record the Burdette reading. Put 10cm³ of ammonium hydroxide in a conical flask. Then add 2 drops of an indicator and place the flask under the burette. Run the acid from the burette until it turns green (neutral). Record the reading of the burette again.