chemistry - atomic structure and the periodic table

• an element is a substance containing only one type of atom
• an atom is the smallest part of an element that can exist
• protons have a charge of +1 and a mass of 1
• neutrons have a charge of 0 and a mass of 1
• electrons have a charge of -1 and a mass of 0
• the mass number is the sum of the number of protons and neutrons
• a compound is a substance formed from 2 or more elements that are chemically bonded to each other in fixed positions
• a mixture is a substance made of 2 or more elements or compounds that are combined but not chemically bonded
• the atomic number is the number of protons in a nucleus
• atoms have an overall neutral charge because they have the same number of protons and electrons
• the diameter of an atom is 1 x 10^-10 m (0.1nm)
• the diameter of a nucleus is 1 x 10^-14m
• the evidence for J.J Thompson’s plum pudding model is that he used cathode ray tubes that showed all atoms contain tiny negatively charged subatomic particles (electrons)
• the evidence for Ernest Rutherford’s nuclear model is that he shot a beam of positively charged particles at a thin sheet of gold foil. some particles were scattered and a few were deflected back. this showed that it was mainly empty space and the positive charge was thought to be evenly spread out
• the evidence for Bohr’s solar model is that he studied the way glowing, hot hydrogen gives off light
• the evidence for James Chadwick’s atomic model is that he managed to eject neutrons from a sample of wax using gamma rays
• a few alpha particles deflected from Chadwick’s model showing that they were repelled by the positive charge in the centre
• group 1 elements are called the Alkali metals
• the elements in group 7 are called the Halogens
• the elements in group 0/8 are called the Noble Gases
• a group is a column going down the periodic table
• a period is a row going across the periodic table
• Döbereiner’s law was the law of triads. he said that the relative atomic mass of the middle element in each group of 3 was similar to the average of the atomic mass of the other 2
• Newland’s law in 1864 was the law of Octaves. he ordered the elements in order of atomic weight. he said that each element was close to the element 8 places ahead
• Mendeleev’s law in 1869 ordered the elements according to their atomic weight. he switched the order of some elements according to their properties and left gaps for undiscovered elements which he predicted the atomic weights of (Germanium and Gallium)
• in 1987 J.J Thompson proposed that the atom was a ball of positive charge with the negatively charged electrons embedded throughout
• in 1911 Ernest Rutherford proposed that the atom consists mainly of empty space with the positive nucleus at the centre and the electrons orbiting in paths around the nucleus
• in 1913 Niels Bohr proposed that electrons orbit the nucleus in fixed shells or orbitals located at set distances from the nucleus
• in 1932 James Chadwick added the idea of the existence of large, neutral particles within the nucleus (neutrons)
• the maximum number of electrons in each shell is 2, 8, 8, 2
• the number of electrons shows the group number
• the number of shells shows the period number
• the shells with the lowest energy are filled first because they are closest to the nucleus
• an isotope is different types of the same element with the same number of protons but a different number of neutrons. this means they have the same atomic number but different mass number
• relative atomic mass (Ar) = (mass of 1st isotope x % of 1st isotope) + (mass of 2nd isotope x % of 2nd isotope) / 100
• group 1 metals are solid at room temperature
• properties of group 1 metals is that they are shiny, soft, low density, good conductors of electricity
• Alkali metals have 1 electron in their outer shell
• an ion is an atom of an element that has lost or gained electrons and has become charged
• in group 1, the reactivity increases as you go down because the electron is further away from the nucleus so the attraction between the electron is weaker and the electron is easily lost