C4 Revision Notes
An atom has a central nucleus surrounded by shells of negatively charged electrons. The nucleus is made up of protons and neutrons, this makes it posititvley charged by the atom overall has now overall charge. This is because it has the same number of protons and electrons, they cancel each other out. An element is made up of one type of atom and a compound is made up of two or more elements that are chemically combined. The mass number is the total number of protons and neutrons in an atom. The atomic number is the number of protons in an atom. The elements in the periodic table are arranged in increasing atomic number. Isotopes are atoms of the same element that have the same atomic number but a different mass number. Each isotope has the same number of protons and electrons but a different number of neutrons. Electronic configuration tells you how the electrons are arranged around the nulceus in shells.
An ion is a charged atom or a group of atoms. A positive ion is made when an atom (or group) loses one or more electrons. A negative ion is made when an atom (or group) gains one or more electron. In ionic bonding, the metal atom loses all outer-shell electrons to become a positive ion. The non-metal atom gains electrons to fill its outer shell and become a negative ion, the positive and negative ions are attracted to each other, this attraction is an ionic bond. Sodium chloride and magnesium oxide form giant ionic lattices in which positive and negative ions are strongly attracted to each other. Therefore they have high melting points, can conduct electricity whne molten but can't when they're solid. When a metal and non-metal combine, electrons are transferred from one atom to the other forming ions. Each will have a complete outer shell (a stable octet). Ions combine to form ionic compounds which have equal amounts of positive and negative charge.
The Periodic Table and Covalent Bonding
Groups are the vertical columns, they all have the same number of electrons in their outer shell in one column, eg. group 2 will have 2 electrons. Periods are the horizontal columns, they all have the same number of occupied electron shells. Ionic bonding is between metals and non-metals, covalent bonding is between non-metals and metallic bonding is between metals. Covalent bonding is when non-metals combine by sharing pairs of electrons. Simple covalently bonded molecules have low melting points, they don't conduct electricity because there aren't any free electrons.
The Group 1 Elements
These are the alkali metals, they all have 1 electron in their outer shell so they have similar properties. They are stored under oil because they react with air and react vigorously with water. Alkali metals react with water to produce hydrogen and a hydroxide, they are soluble and form alkali solutions. they react more vigorously as you go down the group.