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Atomic Structure Noadswood Science, 2012 Wednesday, May 24, 2017 Atomic Structure To know the structure of an atom Electrons Nucleus containing protons and neutrons Periodic Table What is the periodic table and what does it show? There are over 100 different elements, arranged in a chart called the periodic table – the elements are arranged in a special way… Chemical Symbols Every element has its own chemical symbol – it is usually one or two letters long (but can sometimes be three) Every symbol begins with a capital The second and third letters are lower case Examples Mg Mg MG mG O o OO oo na NA nA Na AG Ag ag aG Chemical Symbols Sometimes the symbols are really obvious: O = oxygen; Li = lithium; Mg = magnesium However sometimes it is not easy to tell what the symbol stands for (because the symbol come from a name that is not an English word) E.g. W stands for tungsten (from the word wolfram); Na for sodium (from natrium) The chemical symbols are used all over the world, not matter what language people speak Periodic Table Arrangement The vertical columns in the periodic table are called groups – each group contains elements that have similar properties The periodic table has eight main groups, e.g. group 1 contains very reactive metals such as sodium (Na) and potassium (K) whilst group 7 contains very reactive nonmetals such as chlorine (Cl) and bromine (Br) The horizontal rows are called periods (each new period represents another full shell of electrons) The metals are on the left, the non-metals on the right Atoms – Early Ideas The word atom comes from atomos, an ancient Greek word meaning indivisible: the Greek philosopher Demokritos (460370 BCE) maintained that all matter could be divided and sub-divided into smaller and smaller units, and eventually there would be a tiny particle that could not be divided any further - an atom Understanding of atoms didn’t progress much beyond Demokritos’ theory until the English chemist John Dalton (1766 - 1844) started to look at it in the 1800s… Atoms – Early Ideas Dalton came to the following conclusions: All matter is made of atoms, and atoms are indestructible and cannot be broken down into pieces All the atoms of a particular element are identical to each other and different from the atoms of other elements Atoms are rearranged in a chemical reaction Compounds are formed when two or more different kinds of atoms join together Atoms How can we represent an atom? What does an atom contain? Atoms have a small central nucleus (containing protons and neutrons) which is orbited by electrons All substances are made from atoms, and any given element is made of atoms of just one particular sort – represented by a specific chemical symbol Atom Structure The nucleus: In the middle of the atom Contains protons and neutrons Has a positive (+ve) charge (due to the presence of the protons) Almost the whole mass of the atom is concentrated within the nucleus Size is tiny compared to the atom as a whole! Electrons Nucleus containing protons and neutrons The electrons: - Particle Mass Charge Proton 1 +1 Neutron 1 0 Electron 1/2000 -1 Orbit the nucleus Negatively charged (-ve) Tiny, but cover a lot of space The volume of their orbits determines how big the atom is Virtually no mass They occupy shells around the nucleus Protons & Electrons Neutral atoms have no overall charge – the size of the charge of the electrons is the same as that of the protons, just opposite (electrons are –ve and protons are +ve) This means in an atom the number of protons equals the number of electrons *Electrons can be added / removed – if this is done the charged atom is known as an ion (watch the sweet demo)! Atomic Number & Atomic Mass Periodic table shows one final important piece of information - an element’s atomic number and it’s atomic mass… The mass number (top number) shows the number of protons + neutrons The atomic number (bottom number) shows the number of protons (and therefore, the number of electrons) Mass number Atomic number 16 O O 8 Atomic Number & Atomic Mass Using the periodic table work out how many neutrons, protons and electrons and found in the following atoms: Hydrogen Helium Lithium Carbon Oxygen Protons + neutrons Protons (therefore electrons) O Mass number Atoms Atomic number Remember: The mass number (top number) shows the number of protons + neutrons The atomic number (bottom number) shows the number of protons (and therefore, the number of electrons) Hydrogen: Mass number 1 (1 proton and 0 neutrons) Atomic number 1 (1 proton & 1 electron) Helium: Mass number 4 (2 protons and 2 neutrons) Atomic number 2 (2 protons & 2 electrons) O Mass number Atoms Lithium: Mass number 7 (3 protons and 4 neutrons) Atomic number 3 (3 protons & 3 electrons) Carbon: Mass number 12 (6 protons and 6 neutrons) Atomic number 6 (6 protons and 6 electrons) Oxygen: Mass number 16 (8 protons and 8 neutrons) Atomic number 8 (8 protons and 8 electrons) Atomic number O Bingo Take a mini periodic table If an element is said, you have to find its symbol using the big periodic table (on the board) – if you have that symbol on your mini periodic table you can colour in the square The winner is the person who gets all their elements coloured in first… E.g. If I said oxygen, you would look it up, discovering its symbol is O If you have the O symbol on your mini periodic table then colour it in! Periodic Table