chemistry p1 t1

• electrons: they are found outside the nucleus in electron shells. They have a charge of -1 and a mass of 1/1835 negligible.
• protons: they are found at the centre of the nucleus. They have a charge of +1 and a mass of 1.
• neutrons: they are found at the centre of the nucleus. They have a charge of 0 and a mass of 1.
• isotope: atoms of an element with the same number of protons and electrons but a different amount of neutrons. The atomic number is the same and the mass number is different.
• RAM = (mass of isotope 1 x % of isotope 1) + (mass of isotope 2 x % of isotope 2) / 100
• rutherford's experiment: he fired positively charged alpha particles at a thin sheet of gold foil to determine how large the nucleus of an atom was. He discovered that 1 in every 20000 bounced back, showing the nucleus was very small.
• John Dalton: he believed all substances were made up of atoms and that atoms were indivisible. He believed that atoms of the same element were exactly alike, and that atoms could join with other atoms to make new substances.
• JJ Thomson: he discovered that atoms can be divided into smaller parts and he proposed the plum pudding model.
• Rutherford discovered that the nucleus of an atom was positive, that atoms are mostly empty space and that electrons travel in random paths around the nucleus.
• the electron configuration describes the arrangement of electrons around the nucleus of an atom. The group number tells you the number of electrons in the outer shell. The period number tells you the number of electron shells.
• periods are rows on the periodic table and groups are columns on the periodic table.
• mendeleev: when he wrote his version of the periodic table, scientists only knew about 40 elements. He left gaps in the table for elements which hadn't been discovered. He arranged the elements based on increasing atomic mass.
• modern periodic table: metals are found on the left side and non-metals are on the right. The elements are organised by atomic number (number of protons and electrons). Moving to the right, the number of electrons in the outer shell increases. Moving down, the number of electron shells increases.
• ion: an atom or molecule with an electric charge due to the loss or gain of electrons.
• ionic compound: a chemical compound formed of oppositely charged ions, held together by strong electrostatic forces. They have a lattice structure.
• ionic bonding: metal atoms lose electrons to become positive cations and non-metal atoms gain electrons to become negative anions.
• when you have a metal and non-metal, the ionic compound ends in -ide.
• when you have a metal, non-metal and oxygen, the ionic compound ends in -ate.
• the ionic properties are a high melting point and boiling point and the ability to conduct electricity when molten or in aqueous solution.
• ionic compounds have a high m.p and b.p due to lots of energy being needed to break the strong ionic bonds.
• ionic compounds conduct electricity when the charge particles are able to move freely.
• covalent bond: a pair of electrons shared between 2 non-metal atoms in order to become stable.
• diatomic: exists as a pair.
• metallic bonding is between 2 metals. Metal atoms are closely packed together so their electron shells overlap. The electrons delocalise and create a sea of electrons.
• properties of metals: high m.p and b.p, magnetic and good conductors. Metals are also malleable due to layers being able to slide over each other.
• some diagrams to show bonds are the 2D space filling model, the 3D ball and stick model and a dot and cross diagram.
• simple covalent molecules: they have strong covalent bonds, weak electrostatic attraction, low m.p and b.p and are poor conductors.
• giant covalent molecules: they have strong covalent bonds, high m.p and b.p and are poor conductors.
• allotrope: different structural forms of the same element.
• some carbon allotropes are diamond, graphite, graphene and fullerenes.
• diamond: is it a giant covalent structure with 4 c-c bonds and a high m.p. It doesn't conduct electricity. It can be used in cutting equipment.
• graphite: it is a giant covalent structure with 3 c-c bonds and it has a high m.p. The layers are able to slide over each other and it can conduct electricity. It is used for electrodes and as a lubricant.
• graphene: it is giant covalent structure with 3 c-c bonds and a high m.p. It is a single layer of graphite and it conducts electricity. It is used in carbon nanotubes.
• fullerenes: it is a simple molecular structure made of 60 carbon atoms. It has a low m.p and can be used in some lubricants.
• ductile: made into thin wires.
• compound: a chemical containing 2 or more different elements that are chemically bonded.
• molecular formula: the number of atoms of each element in a molecule.
• relative formula mass: the mass of all the ions in the compound.
• empirical formula: the simplest whole number ratio of atoms or ions in a substance. To work this out do the mass / RAM and then divide the answers by the smallest number.
• law of conservation of mass: (within and closed system) mass is never lost or gained during a chemical or physical change.