Everything around us and in us is made of elements Everything around us and in us is made of elements!!! Let’s learn about what elements are made of.

18. Elements Elements are a substance that can not be separated or broken down into simpler substances by chemical means. Each element contains only one set of particles. These particles are called atoms.

Example: the element copper is made of only copper atoms

19. Atoms Atom: the smallest unit of matter that retains the identity of the substance

20.Atomic Structure Atoms are composed of 2 regions: Nucleus: the center of the atom that contains the mass of the atom Electron cloud: region that surrounds the nucleus that contains most of the space in the atom

What’s in the Nucleus? The nucleus contains 2 of the 3 subatomic particles and most of the mass of an atom: Protons: positively charged subatomic particles Neutrons: neutrally charged (no charge) subatomic particles

Electrons The 3rd subatomic particle resides outside of the nucleus in the electron cloud Electron: the subatomic particle with a negative charge and relatively no mass

How do these particles interact? Protons and neutrons live compacted in the tiny positively charged nucleus accounting for most of the mass of the atom The negatively charged electrons are small and have a relatively small mass but occupy a large volume of space outside the nucleus

Using the Periodic Table of Elements to find Out the Number of Protons, Neutrons, and Electrons in Each Atom The atomic number is the number located on top and the atomic mass/weight is the decimal number located on the bottom. - As in this example for krypton:

Finding the Number of Protons The atomic number is the number of protons in an atom of an element. In our example, krypton's atomic number is 36. This tells us that an atom of krypton has 36 protons in its nucleus.

Protons The interesting thing here is that every atom of krypton contains 36 protons. If an atom doesn't have 36 protons, it can't be an atom of krypton. Adding or removing protons from the nucleus of an atom creates a different element. For example, removing one proton from an atom of krypton creates an atom of bromine. No two elements have the same number of protons. So, it’s the atomic number that identifies an element…it’s ID #!

The Number of Electrons is... By definition, atoms have no overall electrical charge. That means that there must be a balance between the positively charged protons and the negatively charged electrons. Atoms must have equal numbers of protons and electrons. # Protons = # of Electrons

Losing Electrons An atom can gain or lose electrons, becoming what is known as an ion. Don’t worry, we will get to that later!

The Number of Neutrons… The atomic mass is basically a measurement of the total number of particles in an atom's nucleus. Protons and neutrons are in the nucleus. Atomic mass (Nucleus)= (Number of Protons) + (Number of Neutrons)

The Number of Neutrons… So then….to find the number of neutrons, all you need to do is … Round the atomic mass to the nearest whole number Subtract the number of protons (Atomic Number) from the atomic mass.

Step 1-Round the atomic mass to the nearest whole number In our example, krypton's atomic mass is 84 . * 83.80, rounds up to 84.

Step 2 for neutrons… Then all we have to do is plug in the numbers… Atomic mass -atomic number = # of neutrons 84-36 = 48 Krypton has 48 neutrons

21. In Summary... For any element: Atomic Number = Number of Protons Number of Protons = Number of Electrons Number of Neutrons = Atomic Mass (rounded) - Atomic Number