3. Models of Atomic Structure 1. definitions 3. Models of Atomic Structure Sodium 2,8,1 atom All substances are made of atoms! They are the smallest part of an element that can exist (about 0.1 nm in size) Element A substance made of only one type of atom. Atoms of each element have a chemical symbol, eg O is oxygen. compound contain two or more elements chemically combined in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed. mixture consists of two or more elements or compounds not chemically combined together. Atomic no. Number of protons in an atom. Atoms of the same element have the same number of protons. Mass no. The sum of protons and neutrons in an atom Isotopes Atoms of the same element with a different number of neutrons. Relative atomic mass The average mass of an atom of an element, taking into account the % of each isotope. Metals Found on the LHS of the periodic table. Form positive ions. Non-metals Found on the RHS of the periodic table. Form negative ions. Ions Charged particle formed if an atom loses or gains electrons Neils Bohr model Electrons orbit the nucleus at specific distances. Electrons occupy the lowest available energy levels (shells). The inner shell can hol2 2 electrons max, the others can hold up to 8 electrons Plum pudding model Rutherford’s nuclear model Atomic structure Sub atomic particle Charge Mass Proton +1 1 Electron -1 Neutron James Chadwick includes neutrons in the nucleus 2. Separating mixtures by physical processes distillation chromatography crystallisation filtration Key words: atom, element, compound, mixture, atomic number, mass number, electron, proton, neutron, ion, shells, filtration, distillation, chromatography, crystallisation

The periodic table 1. Development of the periodic table Elements were arranged in order of atomic weight but some elements didn’t fit the pattern Mendeleev left gaps for elements that had not been discovered and changed the order in some places. Elements with properties predicted by Mendeleev discovered and filled the gaps. 4. Group 1- the alkali metals 1 electron in outer shell Soft metals with low density React with non-metals to form ionic compounds where the metal is a +1 ion. These are white solids that dissolve in water forming colourless solution React with water, releasing hydrogen and hydroxides that dissolve in water to give alkaline solutions More reactive further down the group, because the outer electron is further from the nucleus, and more easily the electron is lost. 5. Group 7- the halogens 7 electrons in outer shell Non-metals Diatomic molecules (made of pairs of atoms) React with metals to form ionic compounds where the halide ion has a -1 ion From molecular compounds with other non-metallic elements The further down the group, the higher the relative molecular mass, melting point and boiling point Less reactive further down the group, because the outer electrons are further from the nucleus, and less easily gained. 2. Arrangement of the modern periodic table Elements are in order of atomic number The columns are groups The rows are periods. Elements in the same group have the same number of electrons in their outer shell. This gives them similar chemical properties. Elements in the same period have the same number of shells. 3. Non-metals Found towards the right and top of the periodic table React to form negative ions : The periodic table 6. Group 0 – noble gases Filled outer shell of electrons is a stable arrangement, and so they are unreactive elements The boiling points increase going down the group. 3. Metals On the LHS and towards the bottom of the periodic table React to form positive ions Key words: periodic table, group, period, metal, alkali metals, halogens, noble gases, ion, Mendeleev