Unit 2 Notes

Nucleus

Made up of a protons and neutrons and contains most of an atoms mass

Electron cloud

Region of space with a 90-95% chance of finding an electron. Contains most of an atoms volume

atomic number

identifies the element. The number of protons in the atom.

mass number

the total number of protons and neutrons

Ions

atoms that have a charge, gaining or losing e

Isotope

atoms of the same element with different mass numbers

anion

negatively charged ion

cation

a positively charged ion

positron

a positively charged electron

Stable isotope

n/z ratio equals 1

unstable isotope

n/z ration is greater than 1

alpha particle

a helium nucleus, has mass

beta particle

high speed electrons, no mass but does have charge

gamma particles

highly energetic photons of light, no mass and no charge

chemical reactions

changes one or more substances into a new substance. Atoms are rearranged, but the nucleus stays the same

nuclear reaction

A change in the nucleus of an atom, atomic # changes; the only way to change one element into another.

half-life

time it takes for ½ a radioactive nuclei to decay

electron

negatively charged subatomic particle