CHAPTER 15 Introduction to Atoms

ATOMS are the building block of all matter.

Structure Atoms are made of small particles Consist of Protons, neutrons and electrons (subatomic particles) Consist of nucleus – made of protons (+) and neutrons (neutral) makes up most of the mass of an atom Electron cloud – contains electrons (-) that move around the nucleus (1/10,000 the size of a proton or neutron) Same number of protons and electrons, atom has a neutral charge.

Draw a picture of an atom in your note. Label the electron cloud.

Electron Cloud Sphere shaped region surrounding the nucleus Low energy electrons = closer to nucleus Higher energy electrons = farther away. VALENCE ELECTRONS – electrons far from the nucleus, can move to other atoms Composes most of the volume of an atom. Made mainly of “empty space” – absolutely nothing

Atoms and Elements Elements – type of matter that cannot be broken down, consist of one kind of atom Each atom is unique has its own  ATOMIC NUMBER – number of protons in the nucleus (carbon 6, oxygen 8), also tells the number of electrons

Atomic mass – average mass of all the atoms of an element measured in atomic mass units (amu) 1 proton= 1amu, 1 neutron= 1amu We use the Mass Number – rounded atomic mass

ATOM MATH RULES Atomic # = #protons = #electrons Atomic Mass = #neutron + #protons Atomic Mass - #protons = #neutrons

How many different kinds of atoms are there in the world? Atoms are like letters, you put them together to make compounds or molecules (words)