Structure of the Atom (Section 4.2)

Subatomic Particles Light up your old tv screen When the beam sweeps across your screen it lights up spots There are three beams, one for each primary color of light Red Green Blue Particles in the beams are subatomic particles

Properties of Subatomic Particles Protons, electrons, and neutrons are subatomic particles Protons - a positively charged subatomic particle that is found in the nucleus of an atom Charge is +1, Mass = 1 Electrons - a negatively charged subatomic particle that is found in the space outside the nucleus Charge is -1, mass = 1/2000 Greek word means amber Neutrons - a neutral subatomic particle that is found in the nucleus of an atom, no charge Mass is almost exactly equal to that of a proton (mass = 1)

Comparing Subatomic Particles Protons, electrons, and neutrons can be distinguished by mass, charge, and location in an atom Protons and neutrons have almost the same mass Protons have a positive charge Neutrons have no charge Both are found in the nucleus

Comparing Subatomic Particles Electrons have a mass about 2000 times smaller than that of a proton But its charge is equal in size to and opposite of the charge of a proton Found in the space outside the nucleus

Atomic Number The atomic number of an element equals the number of protons in an atom of that element Atoms of different elements have different numbers of protons Can be used to refer to different elements Atomic number is also the number of electrons for an atom because the charges are balanced

Mass Number Mass number - The sum of the protons and neutrons in the nucleus of an atom Mass # = # protons + # neutrons To find the number of neutrons in an atom subtract the atomic number from the mass number # neutrons = mass # - Atomic #

Isotopes Isotopes - atoms of the same element that have different numbers of neutrons and therefore different mass numbers Isotopes of an element have the same atomic number but different mass numbers because they have different numbers of neutrons Every atom of oxygen has 8 protons but some atoms have 8 or 9 or even 10 neutrons Atoms with 8 have a mass number of 16 Atoms with 9 have a mass number of 17 Atoms with 10 have a mass number of 18

Isotopes With most elements it is hard to notice any differences in the physical or chemical properties between the isotopes Hydrogen-1 only has 1 proton and no neutrons Hydrogen-2 has 1 proton and 1 neutron which doubles its mass, water that contains hydrogen-2 is called heavy water