Chemistry atoms T2

plum pudding model

atoms imagined as positively charged sphere with negative electrons scattered throughout balancing out neutral. no nucleus, mass spread

Gold foil proves

alpha particles mostly went through- empty space some close to positive dense nucleus deflected repelling alpha particles disproving plum model

Atomic number

number of protons in an atom

mass number

number of protons and neutrons

Alpha

4 a 2, 4 He 2, 2 protons and neutrons, helium nucleus can be stopped by paper most ionising weakest penetrating

Beta

0 B -1, 0 e -1, an electron add one, stopped by aluminium medium ionising and penetrating

Gamma

0 y 0, high energy electromagnetic ray can be stopped by lead least ionising strongest penetrating

half life

time taken for half of the radioactive nuclei un a sample to decay

smoke detectors radiation

alpha is used as it is not very penetrating and can be stopped by air or paper making it safe for household detects airflow change by smoke

beta and gamma in smoke detectors

cannot be used as they are more penetrating and dangerous they can pass through human tissue increasing risk and makes it harder for smoke to interrupt and sense

smoke detectors disposal safe

alpha radiation cannot penetrate skin or even air making it safe contained and weak