Elements Isotopes and Ions

Current atomic model An atom is mostly empty space surrounding a tiny nucleus Nucleus contains protons (positively charged particles) and neutrons (particles with no charge) An electron is a negatively charged particle that moves in the space surrounding the nucleus

Elements Elements are pure substances made from atoms that all have the same number of protons Number of protons in the atom of an element is the element’s atomic number

Atomic number and the periodic table How can you find out how many protons an element has if you don’t know the atomic number? You use the periodic table of elements. How to solve for protons? Atomic number = # of protons

Finding the number of electrons Atoms have no overall electrical charge There must be a balance between the positively charged protons and negatively charged electrons # of protons = # of electrons

Atomic mass and mass number Atomic mass is the weighted average mass of the mixture of the element’s isotopes. Each proton has a mass of 1 amu Each neutron has a mass of 1 amu Electrons are so small that they have a mass unit of almost zero Mass number is the sum of the number of protons and neutrons You can find the number by rounding the atomic mass Protons + Neutrons = mass number

Finding the number of neutrons You round the atomic mass and subtract the atomic number to solve for the number of neutrons

Isotopes – Different numbers of neutrons The nucleus contains protons and neutrons Atoms of the same element ALWAYS have the same number of protons… However, atoms of the same elements SOMETIMES have different number of neutrons These are called ISOTOPES

Isotopes Isotopes – atoms that have the same number of protons but different number of neutrons Each element has a limited number of isotopes that occur naturally Some can be radioactive (pg 199)

Using Isotopes Radioactive isotopes have unstable nuclei that break down and release particles, radiation and energy This can be used for dating bones, determining ages of rocks and fossils, diagnose and treat many medical conditions

Ions – gaining or losing electrons Atoms are neutral because the number of protons (+) and electrons (-) are equal However, atoms can lose or gain electrons This means the atom is no longer neutral and has become an ion Ion is an atom that has gained or lost electrons