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Chemistry to Introduction An atom… • is the smallest unit of any given element • consists of 3 main subatomic particles – protons – neutrons – electrons Protons… • have a positive charge (+) • have a mass of 1 atomic mass unit (amu) • are inside the nucleus of the atom Neutrons… • have no charge (neutral or zero) • have a mass of 1 atomic mass unit (amu) • are inside the nucleus of the atom Electrons… • have a negative charge (-) • mass is so small – is insignificant to the total mass of the atom • orbit around the outside of the nucleus Think of a football stadium… • as a giant model of a hydrogen atom – football would be nucleus • 1 proton and 1 neutron inside – the electron would be in farthest seats • not just sitting – electrons are constantly in motion » except at Absolute Zero Electron motion • attractive force between + and – – keeps it from flying away • the faster it moves – the further away it gets • motion keeps it from collapsing on itself • heat makes an electron speed up – so facilitates many reactions Atomic number • number of protons in the atom • whole number in box for each element on periodic table • give atomic number for: – hydrogen – carbon – sodium Give name and symbol for… • the element that has the atomic number 2 9 4 Atomic number/number of protons • never changes – so used to identify the element – on periodic table • increases from left to right and top to bottom Mass number • each proton and each neutron has a mass of 1 atomic mass unit (amu) • mass number is number of protons plus number of neutrons • e.g. an atom has 6 protons and 6 neutrons – its mass number is 6 + 6 = 12 amu – what element is this?