Chemistry EOY Notes 2024 PDF

Chemistry notes (EOY exam 2024) =============================== Atoms ===== History of the atom ------------------- - All matter is made up of tiny particles of different kinds - Atoms are not the smallest -- they are smallest that have different chemical properties - 92 naturally occ...

Chemistry notes (EOY exam 2024) =============================== Atoms ===== History of the atom ------------------- - All matter is made up of tiny particles of different kinds - Atoms are not the smallest -- they are smallest that have different chemical properties - 92 naturally occurring atoms on earth - Taken thousands of years to gain present understanding on what an atom is - Most of our knowledge is less that 100 years old - Atoms first suggested 2500 years ago by Greek philosopher Democritus - Rutherford made his model by firing alpha particles at sheet of gold, seeing what paths they took ### Timeline - 400BC -- Democritus said all substances contained tiny indestructible particles - 1808 -- John Dalton said: - All matter is made of tiny things called atoms - Atoms could not be divided - Atoms of the same element were the same - Atoms combined in simple whole number ratios - 1897 -- English scientist Sir JJ Thomson made plum-pudding model: - atoms contained negatively charged particles called electrons - Atoms are positively charged spheres - Atoms had electrons embedded into them - 1911 -- Lord Rutherford said that: - Atoms are mostly empty space - Dense nucleus with positively charged protons in the middle - Negatively charged electrons orbit nucleus - Flaw: said electrons will eventually lose energy & spin to nucleus - 1913: Niels Bohr modified model: - Electrons orbit nucleus at different energy levels - Specific amounts of energy needed for each level - Said electrons can move shells by gaining or losing energy - 1932: Sir James Chadwick discovered: - The nucleus contains neutrons and protons - Neutrons have same mass as proton - Stop protons from repelling each other The current model ----------------- - Consists of a small dense nucleus made of neutrons and protons, surrounded by spinning electrons - Electron is 1/2000^th^ size of proton & neutron - Neutrons and protons bound by very strong nuclear forces - This stops protons from pushing away from each other - Attractive force between electrons and protons -- keeps electrons moving around nucleus - Most of the atom is empty space - Atoms look like solid balls -- blur from electrons moving around - Sometimes called electron cloud - Number of protons determines which atom it is - Substances that are only 1 kind of atom is called an element - Electrons are always found in regions called electron shells Electron shells --------------- - All neutral atoms have same amount of electrons as protons - Simplest atom, Hydrogen -- 1 proton and 1 neutron - Electrons move between shells so they don't run into each other - Each shell only has room for a certain amount of electrons - 2,8,8,2 formation -- first shell can fit 2, second can fit 8 etc. - Shells closest to nucleus contain lowest amounts of energy - Electron arrangement can be written by showing number of electrons in ech shell from innermost shell -- e.g. Aluminium has 13 electrons -- 2,8,3 Ions ---- - Ion is an atom that has gained or lost electrons - Positive ions have lost electrons, negatived have gained electrons - Positive ion is called a cations - Negative ion is called an anion - When the outer shell is full, atom is more stable - Atoms can lose or gain electrons so they become stable - Atoms will always find the easiest way to gain a full valence shell - Noble gasses already have full valence shell, so do not create ions - Positive ions keep name - Negative ions take first part of element and add -ide to end Writing symbols for ions ------------------------ - Show whether ion is positive or negative using superscript - Also show how many electrons have been gained or lost - E.G. Calcium -- Ca^2+^, Chlorine -- Cl^-^ Periodic table of elements -------------------------- - Russian chemist Dmitri Mendeleev confidently predicted properties of Germanium 15 years before it was discovered - He did this using the periodic table - 2000 years ago, only 10 elements were identified - By early 19^th^ century, \>50 elements had been discovered - Scientists were looking for patterns among elements to classify them - 1964 -- John Newlands arranged elements in increasing atomic weight - Found every 8^th^ element shared similar properties - 1869 -- Mendeleev discovered a way of organising elements into rows and columns - Rows of increasing atomic mass - Called rows periods and columns groups - Called periodic table because elements with similar properties occur at regular intervals - Mendeleev was so confidant that he deliberately left gaps - He predicted the properties of elements that would fill gaps - Periodic table includes names, symbols and atomic numbers of all known elements Counting sub-atomic particles ----------------------------- - Atomic number is the number of protons in the element - Atoms with same atomic number have identical properties - Atomic mass is the sum of the number of protons and neutrons - Number of neutrons can be found by subtracting atomic number from atomic mass - number of protons is the same as electrons, so electrons can be found with atomic number Families of elements -------------------- - periodic table contains 18 groups of elements, some have special names - Group 1: Alkali metals -- all react strongly with water - Group 2: Alkaline earth metals - Group 17: Halogens - Group 18: Noble gasses - Groups 3-12 -- transition metals Metals and non-metals --------------------- - Line that zigzags through periodic table separates metals from non-metals - ¾ are metals - Metals found on left hand side of table - Non-metals are on upper right side of the table - Elements that fall along line are called metalloids -- e.g. silicon, boron Following a trend ----------------- - Many repeating patterns in the periodic tabke - Most obvious is metals on the left to non-metals on the right - Atomic number increases diagonally left - Metallic character increases diagonally downwards and to the right Explaining the periodic table ----------------------------- - Atoms in the same group have similar properties as they have the same number of atoms in valence shells - Number of electrons relates to group number - All elements in group 1 have 1 electron in electron shell - All noble gasses have full valence shells - Period number says the number of shells on the atom - First shell can hold 2 electrons, so there are 2 elements in the period, etc. - Valence shell of an atom can never hold more than 8 electrons as it would become unstable Molecules and compounds ----------------------- - Atoms are not often on their own - When valence shells of atoms interact they can chemically bond - Bonds can form between the same element and different elements - Atoms bond to get full valence shells Noble gasses ------------ - Noble gasses do not bond with other elements as they have full valence shells - Suggested in 1919 by Irving Langmuir - Other elements react because they are less stable - Become more stable when they gain a full valence shell - Chemical reactions allow this Giving and taking electrons --------------------------- - Atoms that have lost or gained electrons are called ions - Metal atoms have a number of electrons \