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Chemistry
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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?