Radioactivity (6.1-6.9)

• Positively charged nucleus → protons and neutrons
• Surounded by negatively charged electrons
• most of the mass is in the neucleus

• Atoms have a radius of around 0.0000000001 m __ 1x10(-10)___

• Isotopes are atoms with the same number if protons(same element); however different number of neutrons --- remember that the charge does not change so it can only be a neutron that changes
• the nucleus here has 17 PROTONS  and 18 NEUTRONS
• proton/atomic number is 17 and tells us what element it is
• mass/nucleon number is 35 and tells us how many protons and neutrons are in the nucleus

• nucleus contains positive protons and neutral neutrons, it has an overall positive charge
• as most of the mass of the atom comes from protons and neutrons, isotopes with more neutrons have a greater mass

Proton:

• charge =        +1
• mass = 1

Neutron:

• charge = 0 
• mass 1

Electron:

• charge =     -1
• mass= almost 0 (1/2000)

Positron:

• charge=      +1
• mass = almost 0 (1/2000)

• Number of protons = number of electrons
• therefore the charge of the atom is equal

• In current model of the atom, electrons aren't arranged at random but at different energy levels (with fixed levels of energy depending on the atom) and at different distances from the nucleus

• electrons change orbit when there is absorbtion or emission of electromagnetic radiation
• when atoms absorb enegy, for example by absorbing electromagnetic radiation, the electrons are pushed up to higher levels ( further from the nucleus)
• they become 'excited'

• if atoms lose outer electrons→ they have more protons than electrons → become positively charged
• they are called positive ions
• the process is called ionisation