c1 - atomic structure

• The smallest possible units of an element are called atoms.
• atoms of different elements can be combined together to make compounds
• key features of chemical reactions : no atoms are created or destroyed, compounds are broken or formed, at least 1 new substance is created and often accompanied by an energy change
• filtration separates mixtures that contain insoluble solids and liquids (which are soluble)
• crystallisation separates solutions into their different parts: dissolved solids (solutes) and liquids (solvents)
• solution is a liquid that contains a dissolved solid
• atoms have no overall charge because all the subatomic particles cancel each other out
• an elements atomic number is the number of protons it has
• electrons have a relative charge of -1
• neutrons have a relative charge of 0 meaning they are neutral
• relative mass of protons and neutrons is 1
• the relative mass of an electron is rounded to 0
• mass number (top), atomic number (bottom)
• almost all of the atoms mass is concentrated in the nucleus
• the mass number of atom is also called the relative mass
• isotopes are atoms of the same element that have different numbers of neutrons
• The relative atomic mass (Ar) is the average mass of all of the isotopes of an element.
• The isotope abundance tells us how often each different isotope of an element is found.
• protium is the most common isotope of hydrogen
• groups are the columns of the periodic table
• periods are the rows of the periodic table
• main influencers of the periodic table : john Newland and Dimitri mendeleev
• Mendeleev left gaps in his table to place elements not known at the time. By looking at the chemical properties and physical properties of the elements next to a gap, he could also predict the properties of these undiscovered elements.
• properties of noble gases : low density, generally unreactive, exist as single atoms, colourless and low boiling points
• monatomic - exist as single atoms
• halogens are in group 7
• halogens form negative ions, are diatomic molecules (two chemically bonded atoms) and reactivity decreases as you go down the group
• when a metal transfers its outer electron to a halogen a salt is formed (example NaCl)
• more reactive metals displace less reactive ones
• elements in group 1 are alkali metals
• transition metals are found at the centre of the periodic table. To their left is group 2 and to their right is group 3
• in comparison to alkali metals, transition metals are stronger, have higher melting points, higher density and lower reactivity
• transition metals form ions with many different positive charges
• transition metals often used as catalysts
• iron used in the Haber process to catalyse the production of ammonia
• platinum and rhodium used in catalytic converters in cars
• metals lose electrons when they react
• noble gases are in group 0
• a pure substance is a single element or compound
• The atoms in polymers are non-metals, so they are held together by covalent bonds.