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Periodic Table and Atomic Structure (Atom has nucleus containing protons…
Periodic Table and Atomic Structure
Atom has nucleus containing protons +1, relative mass 1 and neutrons 0, relative mass 1.
Has electron shells containing electrons -1, relative mass very small.
Electron shells contain 2, 8, 8 electrons.
Mass number: sum of protons and neutrons.
Atomic number: number of electrons or protons.
Element contains only one type of atom. Compound is 2 or more elements chemically combined together.
Developing model of the atom. Pre 1900 tiny solid spheres that could not be divided. 1897 'Plum pudding', ball of positive charge with electrons embedded in it. 1909 nuclear model, positively charged nucleus at centre, surrounded by electrons. 1913 Bohr model, electrons orbit the nucleus in shells. James Chadwick found evidence to show existence of neutrons.
Rutherford's alpha particle scattering experiment. Most alpha particles passed right through the gold foil, a few were deflected by nucleus and reflected back from the nucleus.
The Periodic Table: Early periodic tables, elements arranged in order of atomic mass. Mendeleev ordered elements according to atomic mass, but moved them if they did not share the properties of the group. He also left gaps for elements not yet discovered. Discovery of isotopes proved him right.
The Periodic Table: elements organised in order of atomic number. Elements in columns are groups and share similar properties. Rows are called periods and are elements that have the same number of electron shells.
Metals: To the left of the Periodic Table. Form positive ions, conductors, high melting and boiling points, ductile and malleable.
Non-metals: To the right of the Periodic Table. Form negative ions, insulators, pow melting and boiling points.
Group 1 Alkali metals: 1 electron in outer shell, form 1+ ions, very reactive with oxygen, water and chlorine. Reactivity increases down the group because the negative outer electron is further away from the positive nucleus so is more easily lost.
Metal + oxygen > metal oxide
Metal + water > metal hydroxide + hydrogen
Metal + chlorine > metal chloride
Group 7 Halogens. 7 electrons in their outer shell. Form 1- ions. Melting and boiling points increase down the group (gas> liquid > solid). Reactivity decreases down the group because increasing proton number means an electron is more easily gained.
Metal + halogen > metal halide
Hydrogen + halogen > hydrogen halide
Displacement reaction. A more reactive halogen will displace the less reactive halogen from the salt. Chlorine + potassium bromide > potassium chloride + bromine
Noble Gases Group 0. Unreactive due to having full outer shells of electrons. Boiling points increase down the group due to increasing atomic number.
Transition metals. Less reactive, harder, denser, higher melting points compared to Group 1. Many have different ion possibilities with different charges. Used as catalysts, form coloured compounds.
Isotopes: atoms of the same element with the same number of protons and different numbers of neutrons. Relative abundance = (% isotope 1) + (% isotope 2 x mass isotope 2) / 100